zstd: Update to pristine 1.3.3

21 files changed, 1521 insertions, 1449 deletions

diff --git a/thirdparty/README.md b/thirdparty/README.md
index 792e3b1650..049ea6e58e 100644
--- a/thirdparty/README.md
+++ b/thirdparty/README.md
@@ -453,10 +453,10 @@ Files extracted from upstream source:
 ## zstd
 
 - Upstream: https://github.com/facebook/zstd
-- Version: 1.3.2
+- Version: 1.3.3
 - License: BSD-3-Clause
 
 Files extracted from upstream source:
 
 - lib/{common/,compress/,decompress/,zstd.h}
-- README.md, LICENSE
+- LICENSE
diff --git a/thirdparty/zstd/common/bitstream.h b/thirdparty/zstd/common/bitstream.h
index 2094823fe2..fcf3843079 100644
--- a/thirdparty/zstd/common/bitstream.h
+++ b/thirdparty/zstd/common/bitstream.h
@@ -167,7 +167,7 @@ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
 /*-**************************************************************
 *  Internal functions
 ****************************************************************/
-MEM_STATIC unsigned BIT_highbit32 (register U32 val)
+MEM_STATIC unsigned BIT_highbit32 (U32 val)
 {
     assert(val != 0);
     {
diff --git a/thirdparty/zstd/common/mem.h b/thirdparty/zstd/common/mem.h
index 23335c3146..47d2300177 100644
--- a/thirdparty/zstd/common/mem.h
+++ b/thirdparty/zstd/common/mem.h
@@ -56,8 +56,6 @@ MEM_STATIC void MEM_check(void) { MEM_STATIC_ASSERT((sizeof(size_t)==4) || (size
   typedef   int32_t S32;
   typedef  uint64_t U64;
   typedef   int64_t S64;
-  typedef  intptr_t iPtrDiff;
-  typedef uintptr_t uPtrDiff;
 #else
   typedef unsigned char      BYTE;
   typedef unsigned short      U16;
@@ -66,8 +64,6 @@ MEM_STATIC void MEM_check(void) { MEM_STATIC_ASSERT((sizeof(size_t)==4) || (size
   typedef   signed int        S32;
   typedef unsigned long long  U64;
   typedef   signed long long  S64;
-  typedef ptrdiff_t      iPtrDiff;
-  typedef size_t         uPtrDiff;
 #endif
 
 
@@ -123,20 +119,26 @@ MEM_STATIC void MEM_write64(void* memPtr, U64 value) { *(U64*)memPtr = value; }
 /* currently only defined for gcc and icc */
 #if defined(_MSC_VER) || (defined(__INTEL_COMPILER) && defined(WIN32))
     __pragma( pack(push, 1) )
-    typedef union { U16 u16; U32 u32; U64 u64; size_t st; } unalign;
+    typedef struct { U16 v; } unalign16;
+    typedef struct { U32 v; } unalign32;
+    typedef struct { U64 v; } unalign64;
+    typedef struct { size_t v; } unalignArch;
     __pragma( pack(pop) )
 #else
-    typedef union { U16 u16; U32 u32; U64 u64; size_t st; } __attribute__((packed)) unalign;
+    typedef struct { U16 v; } __attribute__((packed)) unalign16;
+    typedef struct { U32 v; } __attribute__((packed)) unalign32;
+    typedef struct { U64 v; } __attribute__((packed)) unalign64;
+    typedef struct { size_t v; } __attribute__((packed)) unalignArch;
 #endif
 
-MEM_STATIC U16 MEM_read16(const void* ptr) { return ((const unalign*)ptr)->u16; }
-MEM_STATIC U32 MEM_read32(const void* ptr) { return ((const unalign*)ptr)->u32; }
-MEM_STATIC U64 MEM_read64(const void* ptr) { return ((const unalign*)ptr)->u64; }
-MEM_STATIC size_t MEM_readST(const void* ptr) { return ((const unalign*)ptr)->st; }
+MEM_STATIC U16 MEM_read16(const void* ptr) { return ((const unalign16*)ptr)->v; }
+MEM_STATIC U32 MEM_read32(const void* ptr) { return ((const unalign32*)ptr)->v; }
+MEM_STATIC U64 MEM_read64(const void* ptr) { return ((const unalign64*)ptr)->v; }
+MEM_STATIC size_t MEM_readST(const void* ptr) { return ((const unalignArch*)ptr)->v; }
 
-MEM_STATIC void MEM_write16(void* memPtr, U16 value) { ((unalign*)memPtr)->u16 = value; }
-MEM_STATIC void MEM_write32(void* memPtr, U32 value) { ((unalign*)memPtr)->u32 = value; }
-MEM_STATIC void MEM_write64(void* memPtr, U64 value) { ((unalign*)memPtr)->u64 = value; }
+MEM_STATIC void MEM_write16(void* memPtr, U16 value) { ((unalign16*)memPtr)->v = value; }
+MEM_STATIC void MEM_write32(void* memPtr, U32 value) { ((unalign32*)memPtr)->v = value; }
+MEM_STATIC void MEM_write64(void* memPtr, U64 value) { ((unalign64*)memPtr)->v = value; }
 
 #else
 
diff --git a/thirdparty/zstd/common/pool.c b/thirdparty/zstd/common/pool.c
index 1b0fe1035d..98b109e72a 100644
--- a/thirdparty/zstd/common/pool.c
+++ b/thirdparty/zstd/common/pool.c
@@ -11,7 +11,6 @@
 
 /* ======   Dependencies   ======= */
 #include <stddef.h>  /* size_t */
-#include <stdlib.h>  /* malloc, calloc, free */
 #include "pool.h"
 
 /* ======   Compiler specifics   ====== */
@@ -115,7 +114,7 @@ POOL_ctx* POOL_create_advanced(size_t numThreads, size_t queueSize, ZSTD_customM
      * and full queues.
      */
     ctx->queueSize = queueSize + 1;
-    ctx->queue = (POOL_job*) malloc(ctx->queueSize * sizeof(POOL_job));
+    ctx->queue = (POOL_job*)ZSTD_malloc(ctx->queueSize * sizeof(POOL_job), customMem);
     ctx->queueHead = 0;
     ctx->queueTail = 0;
     ctx->numThreadsBusy = 0;
diff --git a/thirdparty/zstd/common/zstd_common.c b/thirdparty/zstd/common/zstd_common.c
index c2041053be..bccc948892 100644
--- a/thirdparty/zstd/common/zstd_common.c
+++ b/thirdparty/zstd/common/zstd_common.c
@@ -31,21 +31,27 @@ const char* ZSTD_versionString(void) { return ZSTD_VERSION_STRING; }
 *  ZSTD Error Management
 ******************************************/
 /*! ZSTD_isError() :
-*   tells if a return value is an error code */
+ *  tells if a return value is an error code */
 unsigned ZSTD_isError(size_t code) { return ERR_isError(code); }
 
 /*! ZSTD_getErrorName() :
-*   provides error code string from function result (useful for debugging) */
+ *  provides error code string from function result (useful for debugging) */
 const char* ZSTD_getErrorName(size_t code) { return ERR_getErrorName(code); }
 
 /*! ZSTD_getError() :
-*   convert a `size_t` function result into a proper ZSTD_errorCode enum */
+ *  convert a `size_t` function result into a proper ZSTD_errorCode enum */
 ZSTD_ErrorCode ZSTD_getErrorCode(size_t code) { return ERR_getErrorCode(code); }
 
 /*! ZSTD_getErrorString() :
-*   provides error code string from enum */
+ *  provides error code string from enum */
 const char* ZSTD_getErrorString(ZSTD_ErrorCode code) { return ERR_getErrorString(code); }
 
+/*! g_debuglog_enable :
+ *  turn on/off debug traces (global switch) */
+#if defined(ZSTD_DEBUG) && (ZSTD_DEBUG >= 2)
+int g_debuglog_enable = 1;
+#endif
+
 
 /*=**************************************************************
 *  Custom allocator
diff --git a/thirdparty/zstd/common/zstd_internal.h b/thirdparty/zstd/common/zstd_internal.h
index e91cd20baa..5d2900eb76 100644
--- a/thirdparty/zstd/common/zstd_internal.h
+++ b/thirdparty/zstd/common/zstd_internal.h
@@ -11,6 +11,10 @@
 #ifndef ZSTD_CCOMMON_H_MODULE
 #define ZSTD_CCOMMON_H_MODULE
 
+/* this module contains definitions which must be identical
+ * across compression, decompression and dictBuilder.
+ * It also contains a few functions useful to at least 2 of them
+ * and which benefit from being inlined */
 
 /*-*************************************
 *  Dependencies
@@ -50,21 +54,26 @@ extern "C" {
 
 #if defined(ZSTD_DEBUG) && (ZSTD_DEBUG>=2)
 #  include <stdio.h>
+extern int g_debuglog_enable;
 /* recommended values for ZSTD_DEBUG display levels :
  * 1 : no display, enables assert() only
- * 2 : reserved for currently active debugging path
- * 3 : events once per object lifetime (CCtx, CDict)
+ * 2 : reserved for currently active debug path
+ * 3 : events once per object lifetime (CCtx, CDict, etc.)
  * 4 : events once per frame
  * 5 : events once per block
  * 6 : events once per sequence (*very* verbose) */
-#  define DEBUGLOG(l, ...) {                         \
-                if (l<=ZSTD_DEBUG) {                 \
-                    fprintf(stderr, __FILE__ ": ");  \
-                    fprintf(stderr, __VA_ARGS__);    \
-                    fprintf(stderr, " \n");          \
+#  define RAWLOG(l, ...) {                                      \
+                if ((g_debuglog_enable) & (l<=ZSTD_DEBUG)) {    \
+                    fprintf(stderr, __VA_ARGS__);               \
+            }   }
+#  define DEBUGLOG(l, ...) {                                    \
+                if ((g_debuglog_enable) & (l<=ZSTD_DEBUG)) {    \
+                    fprintf(stderr, __FILE__ ": " __VA_ARGS__); \
+                    fprintf(stderr, " \n");                     \
             }   }
 #else
-#  define DEBUGLOG(l, ...)      {}    /* disabled */
+#  define RAWLOG(l, ...)      {}    /* disabled */
+#  define DEBUGLOG(l, ...)    {}    /* disabled */
 #endif
 
 
@@ -85,9 +94,7 @@ extern "C" {
 #define ZSTD_OPT_NUM    (1<<12)
 
 #define ZSTD_REP_NUM      3                 /* number of repcodes */
-#define ZSTD_REP_CHECK    (ZSTD_REP_NUM)    /* number of repcodes to check by the optimal parser */
 #define ZSTD_REP_MOVE     (ZSTD_REP_NUM-1)
-#define ZSTD_REP_MOVE_OPT (ZSTD_REP_NUM)
 static const U32 repStartValue[ZSTD_REP_NUM] = { 1, 4, 8 };
 
 #define KB *(1 <<10)
@@ -134,28 +141,40 @@ typedef enum { set_basic, set_rle, set_compressed, set_repeat } symbolEncodingTy
 #define LLFSELog    9
 #define OffFSELog   8
 
-static const U32 LL_bits[MaxLL+1] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-                                      1, 1, 1, 1, 2, 2, 3, 3, 4, 6, 7, 8, 9,10,11,12,
+static const U32 LL_bits[MaxLL+1] = { 0, 0, 0, 0, 0, 0, 0, 0,
+                                      0, 0, 0, 0, 0, 0, 0, 0,
+                                      1, 1, 1, 1, 2, 2, 3, 3,
+                                      4, 6, 7, 8, 9,10,11,12,
                                      13,14,15,16 };
-static const S16 LL_defaultNorm[MaxLL+1] = { 4, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1,
-                                             2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 1, 1, 1, 1, 1,
+static const S16 LL_defaultNorm[MaxLL+1] = { 4, 3, 2, 2, 2, 2, 2, 2,
+                                             2, 2, 2, 2, 2, 1, 1, 1,
+                                             2, 2, 2, 2, 2, 2, 2, 2,
+                                             2, 3, 2, 1, 1, 1, 1, 1,
                                             -1,-1,-1,-1 };
 #define LL_DEFAULTNORMLOG 6  /* for static allocation */
 static const U32 LL_defaultNormLog = LL_DEFAULTNORMLOG;
 
-static const U32 ML_bits[MaxML+1] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-                                      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-                                      1, 1, 1, 1, 2, 2, 3, 3, 4, 4, 5, 7, 8, 9,10,11,
+static const U32 ML_bits[MaxML+1] = { 0, 0, 0, 0, 0, 0, 0, 0,
+                                      0, 0, 0, 0, 0, 0, 0, 0,
+                                      0, 0, 0, 0, 0, 0, 0, 0,
+                                      0, 0, 0, 0, 0, 0, 0, 0,
+                                      1, 1, 1, 1, 2, 2, 3, 3,
+                                      4, 4, 5, 7, 8, 9,10,11,
                                      12,13,14,15,16 };
-static const S16 ML_defaultNorm[MaxML+1] = { 1, 4, 3, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1,
-                                             1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-                                             1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,-1,-1,
+static const S16 ML_defaultNorm[MaxML+1] = { 1, 4, 3, 2, 2, 2, 2, 2,
+                                             2, 1, 1, 1, 1, 1, 1, 1,
+                                             1, 1, 1, 1, 1, 1, 1, 1,
+                                             1, 1, 1, 1, 1, 1, 1, 1,
+                                             1, 1, 1, 1, 1, 1, 1, 1,
+                                             1, 1, 1, 1, 1, 1,-1,-1,
                                             -1,-1,-1,-1,-1 };
 #define ML_DEFAULTNORMLOG 6  /* for static allocation */
 static const U32 ML_defaultNormLog = ML_DEFAULTNORMLOG;
 
-static const S16 OF_defaultNorm[DefaultMaxOff+1] = { 1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1,
-                                                     1, 1, 1, 1, 1, 1, 1, 1,-1,-1,-1,-1,-1 };
+static const S16 OF_defaultNorm[DefaultMaxOff+1] = { 1, 1, 1, 1, 1, 1, 2, 2,
+                                                     2, 1, 1, 1, 1, 1, 1, 1,
+                                                     1, 1, 1, 1, 1, 1, 1, 1,
+                                                    -1,-1,-1,-1,-1 };
 #define OF_DEFAULTNORMLOG 5  /* for static allocation */
 static const U32 OF_defaultNormLog = OF_DEFAULTNORMLOG;
 
@@ -167,7 +186,7 @@ static void ZSTD_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 #define COPY8(d,s) { ZSTD_copy8(d,s); d+=8; s+=8; }
 
 /*! ZSTD_wildcopy() :
-*   custom version of memcpy(), can copy up to 7 bytes too many (8 bytes if length==0) */
+ *  custom version of memcpy(), can overwrite up to WILDCOPY_OVERLENGTH bytes (if length==0) */
 #define WILDCOPY_OVERLENGTH 8
 MEM_STATIC void ZSTD_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
@@ -191,17 +210,14 @@ MEM_STATIC void ZSTD_wildcopy_e(void* dst, const void* src, void* dstEnd)   /* s
 
 
 /*-*******************************************
-*  Private interfaces
+*  Private declarations
 *********************************************/
-typedef struct ZSTD_stats_s ZSTD_stats_t;
-
 typedef struct seqDef_s {
     U32 offset;
     U16 litLength;
     U16 matchLength;
 } seqDef;
 
-
 typedef struct {
     seqDef* sequencesStart;
     seqDef* sequences;
@@ -216,100 +232,8 @@ typedef struct {
     U32   repToConfirm[ZSTD_REP_NUM];
 } seqStore_t;
 
-typedef struct {
-    U32 off;
-    U32 len;
-} ZSTD_match_t;
-
-typedef struct {
-    U32 price;
-    U32 off;
-    U32 mlen;
-    U32 litlen;
-    U32 rep[ZSTD_REP_NUM];
-} ZSTD_optimal_t;
-
-typedef struct {
-    U32* litFreq;
-    U32* litLengthFreq;
-    U32* matchLengthFreq;
-    U32* offCodeFreq;
-    ZSTD_match_t* matchTable;
-    ZSTD_optimal_t* priceTable;
-
-    U32  matchLengthSum;
-    U32  matchSum;
-    U32  litLengthSum;
-    U32  litSum;
-    U32  offCodeSum;
-    U32  log2matchLengthSum;
-    U32  log2matchSum;
-    U32  log2litLengthSum;
-    U32  log2litSum;
-    U32  log2offCodeSum;
-    U32  factor;
-    U32  staticPrices;
-    U32  cachedPrice;
-    U32  cachedLitLength;
-    const BYTE* cachedLiterals;
-} optState_t;
-
-typedef struct {
-    U32 offset;
-    U32 checksum;
-} ldmEntry_t;
-
-typedef struct {
-    ldmEntry_t* hashTable;
-    BYTE* bucketOffsets;    /* Next position in bucket to insert entry */
-    U64 hashPower;          /* Used to compute the rolling hash.
-                             * Depends on ldmParams.minMatchLength */
-} ldmState_t;
-
-typedef struct {
-    U32 enableLdm;          /* 1 if enable long distance matching */
-    U32 hashLog;            /* Log size of hashTable */
-    U32 bucketSizeLog;      /* Log bucket size for collision resolution, at most 8 */
-    U32 minMatchLength;     /* Minimum match length */
-    U32 hashEveryLog;       /* Log number of entries to skip */
-} ldmParams_t;
-
-typedef struct {
-    U32 hufCTable[HUF_CTABLE_SIZE_U32(255)];
-    FSE_CTable offcodeCTable[FSE_CTABLE_SIZE_U32(OffFSELog, MaxOff)];
-    FSE_CTable matchlengthCTable[FSE_CTABLE_SIZE_U32(MLFSELog, MaxML)];
-    FSE_CTable litlengthCTable[FSE_CTABLE_SIZE_U32(LLFSELog, MaxLL)];
-    U32 workspace[HUF_WORKSPACE_SIZE_U32];
-    HUF_repeat hufCTable_repeatMode;
-    FSE_repeat offcode_repeatMode;
-    FSE_repeat matchlength_repeatMode;
-    FSE_repeat litlength_repeatMode;
-} ZSTD_entropyCTables_t;
-
-struct ZSTD_CCtx_params_s {
-    ZSTD_format_e format;
-    ZSTD_compressionParameters cParams;
-    ZSTD_frameParameters fParams;
-
-    int compressionLevel;
-    U32 forceWindow;           /* force back-references to respect limit of
-                                * 1<<wLog, even for dictionary */
-
-    /* Multithreading: used to pass parameters to mtctx */
-    U32 nbThreads;
-    unsigned jobSize;
-    unsigned overlapSizeLog;
-
-    /* Long distance matching parameters */
-    ldmParams_t ldmParams;
-
-    /* For use with createCCtxParams() and freeCCtxParams() only */
-    ZSTD_customMem customMem;
-
-};  /* typedef'd to ZSTD_CCtx_params within "zstd.h" */
-
-const seqStore_t* ZSTD_getSeqStore(const ZSTD_CCtx* ctx);
-void ZSTD_seqToCodes(const seqStore_t* seqStorePtr);
+const seqStore_t* ZSTD_getSeqStore(const ZSTD_CCtx* ctx);   /* compress & dictBuilder */
+void ZSTD_seqToCodes(const seqStore_t* seqStorePtr);   /* compress, dictBuilder, decodeCorpus (shouldn't get its definition from here) */
 
 /* custom memory allocation functions */
 void* ZSTD_malloc(size_t size, ZSTD_customMem customMem);
@@ -317,9 +241,7 @@ void* ZSTD_calloc(size_t size, ZSTD_customMem customMem);
 void ZSTD_free(void* ptr, ZSTD_customMem customMem);
 
 
-/*======  common function  ======*/
-
-MEM_STATIC U32 ZSTD_highbit32(U32 val)
+MEM_STATIC U32 ZSTD_highbit32(U32 val)   /* compress, dictBuilder, decodeCorpus */
 {
     assert(val != 0);
     {
@@ -330,66 +252,25 @@ MEM_STATIC U32 ZSTD_highbit32(U32 val)
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* GCC Intrinsic */
         return 31 - __builtin_clz(val);
 #   else   /* Software version */
-        static const int DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
+        static const U32 DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
         U32 v = val;
-        int r;
         v |= v >> 1;
         v |= v >> 2;
         v |= v >> 4;
         v |= v >> 8;
         v |= v >> 16;
-        r = DeBruijnClz[(U32)(v * 0x07C4ACDDU) >> 27];
-        return r;
+        return DeBruijnClz[(v * 0x07C4ACDDU) >> 27];
 #   endif
     }
 }
 
 
-/* hidden functions */
-
 /* ZSTD_invalidateRepCodes() :
  * ensures next compression will not use repcodes from previous block.
  * Note : only works with regular variant;
  *        do not use with extDict variant ! */
-void ZSTD_invalidateRepCodes(ZSTD_CCtx* cctx);
-
-
-/*! ZSTD_initCStream_internal() :
- *  Private use only. Init streaming operation.
- *  expects params to be valid.
- *  must receive dict, or cdict, or none, but not both.
- *  @return : 0, or an error code */
-size_t ZSTD_initCStream_internal(ZSTD_CStream* zcs,
-                     const void* dict, size_t dictSize,
-                     const ZSTD_CDict* cdict,
-                     ZSTD_CCtx_params  params, unsigned long long pledgedSrcSize);
-
-/*! ZSTD_compressStream_generic() :
- *  Private use only. To be called from zstdmt_compress.c in single-thread mode. */
-size_t ZSTD_compressStream_generic(ZSTD_CStream* zcs,
-                                   ZSTD_outBuffer* output,
-                                   ZSTD_inBuffer* input,
-                                   ZSTD_EndDirective const flushMode);
-
-/*! ZSTD_getCParamsFromCDict() :
- *  as the name implies */
-ZSTD_compressionParameters ZSTD_getCParamsFromCDict(const ZSTD_CDict* cdict);
-
-/* ZSTD_compressBegin_advanced_internal() :
- * Private use only. To be called from zstdmt_compress.c. */
-size_t ZSTD_compressBegin_advanced_internal(ZSTD_CCtx* cctx,
-                                    const void* dict, size_t dictSize,
-                                    ZSTD_dictMode_e dictMode,
-                                    ZSTD_CCtx_params params,
-                                    unsigned long long pledgedSrcSize);
-
-/* ZSTD_compress_advanced_internal() :
- * Private use only. To be called from zstdmt_compress.c. */
-size_t ZSTD_compress_advanced_internal(ZSTD_CCtx* cctx,
-                                       void* dst, size_t dstCapacity,
-                                 const void* src, size_t srcSize,
-                                 const void* dict,size_t dictSize,
-                                 ZSTD_CCtx_params params);
+void ZSTD_invalidateRepCodes(ZSTD_CCtx* cctx);   /* zstdmt, adaptive_compression (shouldn't get this definition from here) */
+
 
 typedef struct {
     blockType_e blockType;
@@ -398,7 +279,8 @@ typedef struct {
 } blockProperties_t;
 
 /*! ZSTD_getcBlockSize() :
-*   Provides the size of compressed block from block header `src` */
+ *  Provides the size of compressed block from block header `src` */
+/* Used by: decompress, fullbench (does not get its definition from here) */
 size_t ZSTD_getcBlockSize(const void* src, size_t srcSize,
                           blockProperties_t* bpPtr);
 
diff --git a/thirdparty/zstd/compress/zstd_compress.c b/thirdparty/zstd/compress/zstd_compress.c
index 2c46c79f1c..8d1629246d 100644
--- a/thirdparty/zstd/compress/zstd_compress.c
+++ b/thirdparty/zstd/compress/zstd_compress.c
@@ -26,7 +26,7 @@
 #include "fse.h"
 #define HUF_STATIC_LINKING_ONLY
 #include "huf.h"
-#include "zstd_compress.h"
+#include "zstd_compress_internal.h"
 #include "zstd_fast.h"
 #include "zstd_double_fast.h"
 #include "zstd_lazy.h"
@@ -43,17 +43,6 @@ size_t ZSTD_compressBound(size_t srcSize) {
 
 
 /*-*************************************
-*  Sequence storage
-***************************************/
-static void ZSTD_resetSeqStore(seqStore_t* ssPtr)
-{
-    ssPtr->lit = ssPtr->litStart;
-    ssPtr->sequences = ssPtr->sequencesStart;
-    ssPtr->longLengthID = 0;
-}
-
-
-/*-*************************************
 *  Context memory management
 ***************************************/
 struct ZSTD_CDict_s {
@@ -78,6 +67,7 @@ ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem)
     if (!cctx) return NULL;
     cctx->customMem = customMem;
     cctx->requestedParams.compressionLevel = ZSTD_CLEVEL_DEFAULT;
+    cctx->requestedParams.fParams.contentSizeFlag = 1;
     ZSTD_STATIC_ASSERT(zcss_init==0);
     ZSTD_STATIC_ASSERT(ZSTD_CONTENTSIZE_UNKNOWN==(0ULL - 1));
     return cctx;
@@ -152,28 +142,34 @@ const seqStore_t* ZSTD_getSeqStore(const ZSTD_CCtx* ctx) { return &(ctx->seqStor
 #define ZSTD_CLEVEL_CUSTOM 999
 
 static ZSTD_compressionParameters ZSTD_getCParamsFromCCtxParams(
-        ZSTD_CCtx_params params, U64 srcSizeHint, size_t dictSize)
+        ZSTD_CCtx_params CCtxParams, U64 srcSizeHint, size_t dictSize)
 {
-    return (params.compressionLevel == ZSTD_CLEVEL_CUSTOM ?
-                    params.cParams :
-                    ZSTD_getCParams(params.compressionLevel, srcSizeHint, dictSize));
+    DEBUGLOG(4, "ZSTD_getCParamsFromCCtxParams: srcSize = %u, dictSize = %u",
+                (U32)srcSizeHint, (U32)dictSize);
+    return (CCtxParams.compressionLevel == ZSTD_CLEVEL_CUSTOM) ?
+                CCtxParams.cParams :
+                ZSTD_getCParams(CCtxParams.compressionLevel, srcSizeHint, dictSize);
 }
 
-static void ZSTD_cLevelToCCtxParams_srcSize(ZSTD_CCtx_params* params, U64 srcSize)
+static void ZSTD_cLevelToCCtxParams_srcSize(ZSTD_CCtx_params* CCtxParams, U64 srcSize)
 {
-    params->cParams = ZSTD_getCParamsFromCCtxParams(*params, srcSize, 0);
-    params->compressionLevel = ZSTD_CLEVEL_CUSTOM;
+    DEBUGLOG(4, "ZSTD_cLevelToCCtxParams_srcSize: srcSize = %u",
+                (U32)srcSize);
+    CCtxParams->cParams = ZSTD_getCParamsFromCCtxParams(*CCtxParams, srcSize, 0);
+    CCtxParams->compressionLevel = ZSTD_CLEVEL_CUSTOM;
 }
 
 static void ZSTD_cLevelToCParams(ZSTD_CCtx* cctx)
 {
+    DEBUGLOG(4, "ZSTD_cLevelToCParams: level=%i", cctx->requestedParams.compressionLevel);
     ZSTD_cLevelToCCtxParams_srcSize(
             &cctx->requestedParams, cctx->pledgedSrcSizePlusOne-1);
 }
 
-static void ZSTD_cLevelToCCtxParams(ZSTD_CCtx_params* params)
+static void ZSTD_cLevelToCCtxParams(ZSTD_CCtx_params* CCtxParams)
 {
-    ZSTD_cLevelToCCtxParams_srcSize(params, 0);
+    DEBUGLOG(4, "ZSTD_cLevelToCCtxParams");
+    ZSTD_cLevelToCCtxParams_srcSize(CCtxParams, ZSTD_CONTENTSIZE_UNKNOWN);
 }
 
 static ZSTD_CCtx_params ZSTD_makeCCtxParamsFromCParams(
@@ -251,6 +247,7 @@ static ZSTD_CCtx_params ZSTD_assignParamsToCCtxParams(
 
 size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned value)
 {
+    DEBUGLOG(4, "ZSTD_CCtx_setParameter (%u, %u)", (U32)param, value);
     if (cctx->streamStage != zcss_init) return ERROR(stage_wrong);
 
     switch(param)
@@ -259,7 +256,6 @@ size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned v
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
     case ZSTD_p_compressionLevel:
-        if (value == 0) return 0;  /* special value : 0 means "don't change anything" */
         if (cctx->cdict) return ERROR(stage_wrong);
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
@@ -270,9 +266,8 @@ size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned v
     case ZSTD_p_minMatch:
     case ZSTD_p_targetLength:
     case ZSTD_p_compressionStrategy:
-        if (value == 0) return 0;  /* special value : 0 means "don't change anything" */
         if (cctx->cdict) return ERROR(stage_wrong);
-        ZSTD_cLevelToCParams(cctx);  /* Can optimize if srcSize is known */
+        if (value>0) ZSTD_cLevelToCParams(cctx);  /* Can optimize if srcSize is known */
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
     case ZSTD_p_contentSizeFlag:
@@ -281,15 +276,12 @@ size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned v
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
     case ZSTD_p_forceMaxWindow :  /* Force back-references to remain < windowSize,
-                                   * even when referencing into Dictionary content
+                                   * even when referencing into Dictionary content.
                                    * default : 0 when using a CDict, 1 when using a Prefix */
-        cctx->loadedDictEnd = 0;
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
     case ZSTD_p_nbThreads:
-        if (value==0) return 0;
-        DEBUGLOG(5, " setting nbThreads : %u", value);
-        if (value > 1 && cctx->staticSize) {
+        if ((value > 1) && cctx->staticSize) {
             return ERROR(parameter_unsupported);  /* MT not compatible with static alloc */
         }
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
@@ -298,22 +290,15 @@ size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned v
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
     case ZSTD_p_overlapSizeLog:
-        DEBUGLOG(5, " setting overlap with nbThreads == %u", cctx->requestedParams.nbThreads);
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
     case ZSTD_p_enableLongDistanceMatching:
         if (cctx->cdict) return ERROR(stage_wrong);
-        if (value != 0) {
-            ZSTD_cLevelToCParams(cctx);
-        }
+        if (value>0) ZSTD_cLevelToCParams(cctx);
         return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
 
     case ZSTD_p_ldmHashLog:
     case ZSTD_p_ldmMinMatch:
-        if (value == 0) return 0;  /* special value : 0 means "don't change anything" */
-        if (cctx->cdict) return ERROR(stage_wrong);
-        return ZSTD_CCtxParam_setParameter(&cctx->requestedParams, param, value);
-
     case ZSTD_p_ldmBucketSizeLog:
     case ZSTD_p_ldmHashEveryLog:
         if (cctx->cdict) return ERROR(stage_wrong);
@@ -324,160 +309,167 @@ size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned v
 }
 
 size_t ZSTD_CCtxParam_setParameter(
-        ZSTD_CCtx_params* params, ZSTD_cParameter param, unsigned value)
+        ZSTD_CCtx_params* CCtxParams, ZSTD_cParameter param, unsigned value)
 {
+    DEBUGLOG(4, "ZSTD_CCtxParam_setParameter (%u, %u)", (U32)param, value);
     switch(param)
     {
     case ZSTD_p_format :
         if (value > (unsigned)ZSTD_f_zstd1_magicless)
             return ERROR(parameter_unsupported);
-        params->format = (ZSTD_format_e)value;
-        return 0;
+        CCtxParams->format = (ZSTD_format_e)value;
+        return (size_t)CCtxParams->format;
 
     case ZSTD_p_compressionLevel :
         if ((int)value > ZSTD_maxCLevel()) value = ZSTD_maxCLevel();
-        if (value == 0) return 0;
-        params->compressionLevel = value;
-        return 0;
+        if (value)  /* 0 : does not change current level */
+            CCtxParams->compressionLevel = value;
+        return CCtxParams->compressionLevel;
 
     case ZSTD_p_windowLog :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_WINDOWLOG_MIN, ZSTD_WINDOWLOG_MAX);
-        ZSTD_cLevelToCCtxParams(params);
-        params->cParams.windowLog = value;
-        return 0;
+        DEBUGLOG(4, "ZSTD_CCtxParam_setParameter: set windowLog=%u", value);
+        if (value) {  /* 0 : does not change current windowLog */
+            CLAMPCHECK(value, ZSTD_WINDOWLOG_MIN, ZSTD_WINDOWLOG_MAX);
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.windowLog = value;
+        }
+        return CCtxParams->cParams.windowLog;
 
     case ZSTD_p_hashLog :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_HASHLOG_MIN, ZSTD_HASHLOG_MAX);
-        ZSTD_cLevelToCCtxParams(params);
-        params->cParams.hashLog = value;
-        return 0;
+        if (value) { /* 0 : does not change current hashLog */
+            CLAMPCHECK(value, ZSTD_HASHLOG_MIN, ZSTD_HASHLOG_MAX);
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.hashLog = value;
+        }
+        return CCtxParams->cParams.hashLog;
 
     case ZSTD_p_chainLog :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_CHAINLOG_MIN, ZSTD_CHAINLOG_MAX);
-        ZSTD_cLevelToCCtxParams(params);
-        params->cParams.chainLog = value;
-        return 0;
+        if (value) { /* 0 : does not change current chainLog */
+            CLAMPCHECK(value, ZSTD_CHAINLOG_MIN, ZSTD_CHAINLOG_MAX);
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.chainLog = value;
+        }
+        return CCtxParams->cParams.chainLog;
 
     case ZSTD_p_searchLog :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_SEARCHLOG_MIN, ZSTD_SEARCHLOG_MAX);
-        ZSTD_cLevelToCCtxParams(params);
-        params->cParams.searchLog = value;
-        return 0;
+        if (value) { /* 0 : does not change current searchLog */
+            CLAMPCHECK(value, ZSTD_SEARCHLOG_MIN, ZSTD_SEARCHLOG_MAX);
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.searchLog = value;
+        }
+        return value;
 
     case ZSTD_p_minMatch :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_SEARCHLENGTH_MIN, ZSTD_SEARCHLENGTH_MAX);
-        ZSTD_cLevelToCCtxParams(params);
-        params->cParams.searchLength = value;
-        return 0;
+        if (value) { /* 0 : does not change current minMatch length */
+            CLAMPCHECK(value, ZSTD_SEARCHLENGTH_MIN, ZSTD_SEARCHLENGTH_MAX);
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.searchLength = value;
+        }
+        return CCtxParams->cParams.searchLength;
 
     case ZSTD_p_targetLength :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_TARGETLENGTH_MIN, ZSTD_TARGETLENGTH_MAX);
-        ZSTD_cLevelToCCtxParams(params);
-        params->cParams.targetLength = value;
-        return 0;
+        if (value) { /* 0 : does not change current sufficient_len */
+            CLAMPCHECK(value, ZSTD_TARGETLENGTH_MIN, ZSTD_TARGETLENGTH_MAX);
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.targetLength = value;
+        }
+        return CCtxParams->cParams.targetLength;
 
     case ZSTD_p_compressionStrategy :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, (unsigned)ZSTD_fast, (unsigned)ZSTD_btultra);
-        ZSTD_cLevelToCCtxParams(params);
-        params->cParams.strategy = (ZSTD_strategy)value;
-        return 0;
+        if (value) { /* 0 : does not change currentstrategy */
+            CLAMPCHECK(value, (unsigned)ZSTD_fast, (unsigned)ZSTD_btultra);
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.strategy = (ZSTD_strategy)value;
+        }
+        return (size_t)CCtxParams->cParams.strategy;
 
     case ZSTD_p_contentSizeFlag :
         /* Content size written in frame header _when known_ (default:1) */
-        DEBUGLOG(5, "set content size flag = %u", (value>0));
-        params->fParams.contentSizeFlag = value > 0;
-        return 0;
+        DEBUGLOG(4, "set content size flag = %u", (value>0));
+        CCtxParams->fParams.contentSizeFlag = value > 0;
+        return CCtxParams->fParams.contentSizeFlag;
 
     case ZSTD_p_checksumFlag :
         /* A 32-bits content checksum will be calculated and written at end of frame (default:0) */
-        params->fParams.checksumFlag = value > 0;
-        return 0;
+        CCtxParams->fParams.checksumFlag = value > 0;
+        return CCtxParams->fParams.checksumFlag;
 
     case ZSTD_p_dictIDFlag : /* When applicable, dictionary's dictID is provided in frame header (default:1) */
-        DEBUGLOG(5, "set dictIDFlag = %u", (value>0));
-        params->fParams.noDictIDFlag = (value == 0);
-        return 0;
+        DEBUGLOG(4, "set dictIDFlag = %u", (value>0));
+        CCtxParams->fParams.noDictIDFlag = (value == 0);
+        return !CCtxParams->fParams.noDictIDFlag;
 
     case ZSTD_p_forceMaxWindow :
-        params->forceWindow = value > 0;
-        return 0;
+        CCtxParams->forceWindow = (value > 0);
+        return CCtxParams->forceWindow;
 
     case ZSTD_p_nbThreads :
-        if (value == 0) return 0;
+        if (value == 0) return CCtxParams->nbThreads;
 #ifndef ZSTD_MULTITHREAD
         if (value > 1) return ERROR(parameter_unsupported);
-        return 0;
+        return 1;
 #else
-        return ZSTDMT_initializeCCtxParameters(params, value);
+        return ZSTDMT_CCtxParam_setNbThreads(CCtxParams, value);
 #endif
 
     case ZSTD_p_jobSize :
 #ifndef ZSTD_MULTITHREAD
         return ERROR(parameter_unsupported);
 #else
-        if (params->nbThreads <= 1) return ERROR(parameter_unsupported);
-        return ZSTDMT_CCtxParam_setMTCtxParameter(params, ZSTDMT_p_sectionSize, value);
+        if (CCtxParams->nbThreads <= 1) return ERROR(parameter_unsupported);
+        return ZSTDMT_CCtxParam_setMTCtxParameter(CCtxParams, ZSTDMT_p_jobSize, value);
 #endif
 
     case ZSTD_p_overlapSizeLog :
 #ifndef ZSTD_MULTITHREAD
         return ERROR(parameter_unsupported);
 #else
-        if (params->nbThreads <= 1) return ERROR(parameter_unsupported);
-        return ZSTDMT_CCtxParam_setMTCtxParameter(params, ZSTDMT_p_overlapSectionLog, value);
+        if (CCtxParams->nbThreads <= 1) return ERROR(parameter_unsupported);
+        return ZSTDMT_CCtxParam_setMTCtxParameter(CCtxParams, ZSTDMT_p_overlapSectionLog, value);
 #endif
 
     case ZSTD_p_enableLongDistanceMatching :
-        if (value != 0) {
-            ZSTD_cLevelToCCtxParams(params);
-            params->cParams.windowLog = ZSTD_LDM_DEFAULT_WINDOW_LOG;
+        if (value) {
+            ZSTD_cLevelToCCtxParams(CCtxParams);
+            CCtxParams->cParams.windowLog = ZSTD_LDM_DEFAULT_WINDOW_LOG;
         }
-        return ZSTD_ldm_initializeParameters(&params->ldmParams, value);
+        return ZSTD_ldm_initializeParameters(&CCtxParams->ldmParams, value);
 
     case ZSTD_p_ldmHashLog :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_HASHLOG_MIN, ZSTD_HASHLOG_MAX);
-        params->ldmParams.hashLog = value;
-        return 0;
+        if (value) { /* 0 : does not change current ldmHashLog */
+            CLAMPCHECK(value, ZSTD_HASHLOG_MIN, ZSTD_HASHLOG_MAX);
+            CCtxParams->ldmParams.hashLog = value;
+        }
+        return CCtxParams->ldmParams.hashLog;
 
     case ZSTD_p_ldmMinMatch :
-        if (value == 0) return 0;
-        CLAMPCHECK(value, ZSTD_LDM_MINMATCH_MIN, ZSTD_LDM_MINMATCH_MAX);
-        params->ldmParams.minMatchLength = value;
-        return 0;
+        if (value) { /* 0 : does not change current ldmMinMatch */
+            CLAMPCHECK(value, ZSTD_LDM_MINMATCH_MIN, ZSTD_LDM_MINMATCH_MAX);
+            CCtxParams->ldmParams.minMatchLength = value;
+        }
+        return CCtxParams->ldmParams.minMatchLength;
 
     case ZSTD_p_ldmBucketSizeLog :
         if (value > ZSTD_LDM_BUCKETSIZELOG_MAX) {
             return ERROR(parameter_outOfBound);
         }
-        params->ldmParams.bucketSizeLog = value;
-        return 0;
+        CCtxParams->ldmParams.bucketSizeLog = value;
+        return value;
 
     case ZSTD_p_ldmHashEveryLog :
         if (value > ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN) {
             return ERROR(parameter_outOfBound);
         }
-        params->ldmParams.hashEveryLog = value;
-        return 0;
+        CCtxParams->ldmParams.hashEveryLog = value;
+        return value;
 
     default: return ERROR(parameter_unsupported);
     }
 }
 
-/**
- * This function should be updated whenever ZSTD_CCtx_params is updated.
- * Parameters are copied manually before the dictionary is loaded.
- * The multithreading parameters jobSize and overlapSizeLog are set only if
- * nbThreads > 1.
- *
- * Pledged srcSize is treated as unknown.
+/** ZSTD_CCtx_setParametersUsingCCtxParams() :
+ *  just applies `params` into `cctx`
+ *  no action is performed, parameters are merely stored.
  */
 size_t ZSTD_CCtx_setParametersUsingCCtxParams(
         ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params)
@@ -485,33 +477,14 @@ size_t ZSTD_CCtx_setParametersUsingCCtxParams(
     if (cctx->streamStage != zcss_init) return ERROR(stage_wrong);
     if (cctx->cdict) return ERROR(stage_wrong);
 
-    /* Assume the compression and frame parameters are validated */
-    cctx->requestedParams.cParams = params->cParams;
-    cctx->requestedParams.fParams = params->fParams;
-    cctx->requestedParams.compressionLevel = params->compressionLevel;
-
-    /* Set force window explicitly since it sets cctx->loadedDictEnd */
-    CHECK_F( ZSTD_CCtx_setParameter(
-                   cctx, ZSTD_p_forceMaxWindow, params->forceWindow) );
-
-    /* Set multithreading parameters explicitly */
-    CHECK_F( ZSTD_CCtx_setParameter(cctx, ZSTD_p_nbThreads, params->nbThreads) );
-    if (params->nbThreads > 1) {
-        CHECK_F( ZSTD_CCtx_setParameter(cctx, ZSTD_p_jobSize, params->jobSize) );
-        CHECK_F( ZSTD_CCtx_setParameter(
-                    cctx, ZSTD_p_overlapSizeLog, params->overlapSizeLog) );
-    }
+    cctx->requestedParams = *params;
 
-    /* Copy long distance matching parameters */
-    cctx->requestedParams.ldmParams = params->ldmParams;
-
-    /* customMem is used only for create/free params and can be ignored */
     return 0;
 }
 
 ZSTDLIB_API size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize)
 {
-    DEBUGLOG(4, " setting pledgedSrcSize to %u", (U32)pledgedSrcSize);
+    DEBUGLOG(4, "ZSTD_CCtx_setPledgedSrcSize to %u bytes", (U32)pledgedSrcSize);
     if (cctx->streamStage != zcss_init) return ERROR(stage_wrong);
     cctx->pledgedSrcSizePlusOne = pledgedSrcSize+1;
     return 0;
@@ -523,14 +496,14 @@ size_t ZSTD_CCtx_loadDictionary_advanced(
 {
     if (cctx->streamStage != zcss_init) return ERROR(stage_wrong);
     if (cctx->staticSize) return ERROR(memory_allocation);  /* no malloc for static CCtx */
-    DEBUGLOG(4, "load dictionary of size %u", (U32)dictSize);
+    DEBUGLOG(4, "ZSTD_CCtx_loadDictionary_advanced (size: %u)", (U32)dictSize);
     ZSTD_freeCDict(cctx->cdictLocal);  /* in case one already exists */
     if (dict==NULL || dictSize==0) {   /* no dictionary mode */
         cctx->cdictLocal = NULL;
         cctx->cdict = NULL;
     } else {
         ZSTD_compressionParameters const cParams =
-                ZSTD_getCParamsFromCCtxParams(cctx->requestedParams, 0, dictSize);
+                ZSTD_getCParamsFromCCtxParams(cctx->requestedParams, cctx->pledgedSrcSizePlusOne-1, dictSize);
         cctx->cdictLocal = ZSTD_createCDict_advanced(
                                 dict, dictSize,
                                 dictLoadMethod, dictMode,
@@ -756,10 +729,7 @@ size_t ZSTD_estimateCStreamSize(int compressionLevel) {
 static U32 ZSTD_equivalentCParams(ZSTD_compressionParameters cParams1,
                                   ZSTD_compressionParameters cParams2)
 {
-    U32 bslog1 = MIN(cParams1.windowLog, ZSTD_BLOCKSIZELOG_MAX);
-    U32 bslog2 = MIN(cParams2.windowLog, ZSTD_BLOCKSIZELOG_MAX);
-    return (bslog1 == bslog2)   /* same block size */
-         & (cParams1.hashLog  == cParams2.hashLog)
+    return (cParams1.hashLog  == cParams2.hashLog)
          & (cParams1.chainLog == cParams2.chainLog)
          & (cParams1.strategy == cParams2.strategy)   /* opt parser space */
          & ((cParams1.searchLength==3) == (cParams2.searchLength==3));  /* hashlog3 space */
@@ -778,12 +748,38 @@ static U32 ZSTD_equivalentLdmParams(ldmParams_t ldmParams1,
             ldmParams1.hashEveryLog == ldmParams2.hashEveryLog);
 }
 
+typedef enum { ZSTDb_not_buffered, ZSTDb_buffered } ZSTD_buffered_policy_e;
+
+/* ZSTD_sufficientBuff() :
+ * check internal buffers exist for streaming if buffPol == ZSTDb_buffered .
+ * Note : they are assumed to be correctly sized if ZSTD_equivalentCParams()==1 */
+static U32 ZSTD_sufficientBuff(size_t bufferSize1, size_t blockSize1,
+                            ZSTD_buffered_policy_e buffPol2,
+                            ZSTD_compressionParameters cParams2,
+                            U64 pledgedSrcSize)
+{
+    size_t const windowSize2 = MAX(1, (size_t)MIN(((U64)1 << cParams2.windowLog), pledgedSrcSize));
+    size_t const blockSize2 = MIN(ZSTD_BLOCKSIZE_MAX, windowSize2);
+    size_t const neededBufferSize2 = (buffPol2==ZSTDb_buffered) ? windowSize2 + blockSize2 : 0;
+    DEBUGLOG(4, "ZSTD_sufficientBuff: windowSize2=%u from wlog=%u",
+                (U32)windowSize2, cParams2.windowLog);
+    DEBUGLOG(4, "ZSTD_sufficientBuff: blockSize2 %u <=? blockSize1 %u",
+                (U32)blockSize2, (U32)blockSize1);
+    return (blockSize2 <= blockSize1) /* seqStore space depends on blockSize */
+         & (neededBufferSize2 <= bufferSize1);
+}
+
 /** Equivalence for resetCCtx purposes */
 static U32 ZSTD_equivalentParams(ZSTD_CCtx_params params1,
-                                 ZSTD_CCtx_params params2)
+                                 ZSTD_CCtx_params params2,
+                                 size_t buffSize1, size_t blockSize1,
+                                 ZSTD_buffered_policy_e buffPol2,
+                                 U64 pledgedSrcSize)
 {
+    DEBUGLOG(4, "ZSTD_equivalentParams: pledgedSrcSize=%u", (U32)pledgedSrcSize);
     return ZSTD_equivalentCParams(params1.cParams, params2.cParams) &&
-           ZSTD_equivalentLdmParams(params1.ldmParams, params2.ldmParams);
+           ZSTD_equivalentLdmParams(params1.ldmParams, params2.ldmParams) &&
+           ZSTD_sufficientBuff(buffSize1, blockSize1, buffPol2, params2.cParams, pledgedSrcSize);
 }
 
 /*! ZSTD_continueCCtx() :
@@ -791,7 +787,11 @@ static U32 ZSTD_equivalentParams(ZSTD_CCtx_params params1,
 static size_t ZSTD_continueCCtx(ZSTD_CCtx* cctx, ZSTD_CCtx_params params, U64 pledgedSrcSize)
 {
     U32 const end = (U32)(cctx->nextSrc - cctx->base);
-    DEBUGLOG(4, "continue mode");
+    size_t const windowSize = MAX(1, (size_t)MIN(((U64)1 << params.cParams.windowLog), pledgedSrcSize));
+    size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, windowSize);
+    DEBUGLOG(4, "ZSTD_continueCCtx");
+
+    cctx->blockSize = blockSize;   /* previous block size could be different even for same windowLog, due to pledgedSrcSize */
     cctx->appliedParams = params;
     cctx->pledgedSrcSizePlusOne = pledgedSrcSize+1;
     cctx->consumedSrcSize = 0;
@@ -812,7 +812,6 @@ static size_t ZSTD_continueCCtx(ZSTD_CCtx* cctx, ZSTD_CCtx_params params, U64 pl
 }
 
 typedef enum { ZSTDcrp_continue, ZSTDcrp_noMemset } ZSTD_compResetPolicy_e;
-typedef enum { ZSTDb_not_buffered, ZSTDb_buffered } ZSTD_buffered_policy_e;
 
 /*! ZSTD_resetCCtx_internal() :
     note : `params` are assumed fully validated at this stage */
@@ -821,13 +820,16 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
                                       ZSTD_compResetPolicy_e const crp,
                                       ZSTD_buffered_policy_e const zbuff)
 {
-    DEBUGLOG(4, "ZSTD_resetCCtx_internal");
+    DEBUGLOG(4, "ZSTD_resetCCtx_internal: pledgedSrcSize=%u, wlog=%u",
+                (U32)pledgedSrcSize, params.cParams.windowLog);
     assert(!ZSTD_isError(ZSTD_checkCParams(params.cParams)));
-    DEBUGLOG(4, "pledgedSrcSize: %u", (U32)pledgedSrcSize);
 
     if (crp == ZSTDcrp_continue) {
-        if (ZSTD_equivalentParams(params, zc->appliedParams)) {
-            DEBUGLOG(4, "ZSTD_equivalentParams()==1");
+        if (ZSTD_equivalentParams(zc->appliedParams, params,
+                                zc->inBuffSize, zc->blockSize,
+                                zbuff, pledgedSrcSize)) {
+            DEBUGLOG(4, "ZSTD_equivalentParams()==1 -> continue mode (wLog1=%u, blockSize1=%u)",
+                        zc->appliedParams.cParams.windowLog, (U32)zc->blockSize);
             assert(!(params.ldmParams.enableLdm &&
                      params.ldmParams.hashEveryLog == ZSTD_LDM_HASHEVERYLOG_NOTSET));
             zc->entropy->hufCTable_repeatMode = HUF_repeat_none;
@@ -836,6 +838,7 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
             zc->entropy->litlength_repeatMode = FSE_repeat_none;
             return ZSTD_continueCCtx(zc, params, pledgedSrcSize);
     }   }
+    DEBUGLOG(4, "ZSTD_equivalentParams()==0 -> reset CCtx");
 
     if (params.ldmParams.enableLdm) {
         /* Adjust long distance matching parameters */
@@ -846,7 +849,8 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
                 ZSTD_ldm_getHashPower(params.ldmParams.minMatchLength);
     }
 
-    {   size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, (size_t)1 << params.cParams.windowLog);
+    {   size_t const windowSize = MAX(1, (size_t)MIN(((U64)1 << params.cParams.windowLog), pledgedSrcSize));
+        size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, windowSize);
         U32    const divider = (params.cParams.searchLength==3) ? 3 : 4;
         size_t const maxNbSeq = blockSize / divider;
         size_t const tokenSpace = blockSize + 11*maxNbSeq;
@@ -858,7 +862,7 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
         size_t const h3Size = ((size_t)1) << hashLog3;
         size_t const tableSpace = (chainSize + hSize + h3Size) * sizeof(U32);
         size_t const buffOutSize = (zbuff==ZSTDb_buffered) ? ZSTD_compressBound(blockSize)+1 : 0;
-        size_t const buffInSize = (zbuff==ZSTDb_buffered) ? ((size_t)1 << params.cParams.windowLog) + blockSize : 0;
+        size_t const buffInSize = (zbuff==ZSTDb_buffered) ? windowSize + blockSize : 0;
         void* ptr;
 
         /* Check if workSpace is large enough, alloc a new one if needed */
@@ -874,11 +878,15 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
                 : 0;
             size_t const neededSpace = entropySpace + optSpace + ldmSpace +
                                        tableSpace + tokenSpace + bufferSpace;
+            DEBUGLOG(4, "Need %uKB workspace, including %uKB for tables, and %uKB for buffers",
+                        (U32)(neededSpace>>10), (U32)(tableSpace>>10), (U32)(bufferSpace>>10));
+            DEBUGLOG(4, "chainSize: %u - hSize: %u - h3Size: %u - windowSize: %u - blockSize: %u",
+                        (U32)chainSize, (U32)hSize, (U32)h3Size, (U32)windowSize, (U32)blockSize);
 
             if (zc->workSpaceSize < neededSpace) {  /* too small : resize */
-                DEBUGLOG(5, "Need to update workSpaceSize from %uK to %uK \n",
-                            (unsigned)zc->workSpaceSize>>10,
-                            (unsigned)neededSpace>>10);
+                DEBUGLOG(4, "Need to update workSpaceSize from %uK to %uK",
+                            (unsigned)(zc->workSpaceSize>>10),
+                            (unsigned)(neededSpace>>10));
                 /* static cctx : no resize, error out */
                 if (zc->staticSize) return ERROR(memory_allocation);
 
@@ -901,7 +909,7 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
         zc->consumedSrcSize = 0;
         if (pledgedSrcSize == ZSTD_CONTENTSIZE_UNKNOWN)
             zc->appliedParams.fParams.contentSizeFlag = 0;
-        DEBUGLOG(5, "pledged content size : %u ; flag : %u",
+        DEBUGLOG(4, "pledged content size : %u ; flag : %u",
             (U32)pledgedSrcSize, zc->appliedParams.fParams.contentSizeFlag);
         zc->blockSize = blockSize;
 
@@ -927,7 +935,7 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
 
         /* opt parser space */
         if ((params.cParams.strategy == ZSTD_btopt) || (params.cParams.strategy == ZSTD_btultra)) {
-            DEBUGLOG(5, "reserving optimal parser space");
+            DEBUGLOG(4, "reserving optimal parser space");
             assert(((size_t)ptr & 3) == 0);  /* ensure ptr is properly aligned */
             zc->optState.litFreq = (U32*)ptr;
             zc->optState.litLengthFreq = zc->optState.litFreq + (1<<Litbits);
@@ -951,6 +959,7 @@ static size_t ZSTD_resetCCtx_internal(ZSTD_CCtx* zc,
         }
 
         /* table Space */
+        DEBUGLOG(4, "reset table : %u", crp!=ZSTDcrp_noMemset);
         if (crp!=ZSTDcrp_noMemset) memset(ptr, 0, tableSpace);   /* reset tables only */
         assert(((size_t)ptr & 3) == 0);  /* ensure ptr is properly aligned */
         zc->hashTable = (U32*)(ptr);
@@ -999,15 +1008,16 @@ void ZSTD_invalidateRepCodes(ZSTD_CCtx* cctx) {
 
 /*! ZSTD_copyCCtx_internal() :
  *  Duplicate an existing context `srcCCtx` into another one `dstCCtx`.
- *  The "context", in this case, refers to the hash and chain tables, entropy
- *  tables, and dictionary offsets.
  *  Only works during stage ZSTDcs_init (i.e. after creation, but before first call to ZSTD_compressContinue()).
- *  pledgedSrcSize=0 means "empty" if fParams.contentSizeFlag=1
- *  @return : 0, or an error code */
+ *  The "context", in this case, refers to the hash and chain tables,
+ *  entropy tables, and dictionary references.
+ * `windowLog` value is enforced if != 0, otherwise value is copied from srcCCtx.
+ * @return : 0, or an error code */
 static size_t ZSTD_copyCCtx_internal(ZSTD_CCtx* dstCCtx,
                             const ZSTD_CCtx* srcCCtx,
+                            unsigned windowLog,
                             ZSTD_frameParameters fParams,
-                            unsigned long long pledgedSrcSize,
+                            U64 pledgedSrcSize,
                             ZSTD_buffered_policy_e zbuff)
 {
     DEBUGLOG(5, "ZSTD_copyCCtx_internal");
@@ -1017,6 +1027,7 @@ static size_t ZSTD_copyCCtx_internal(ZSTD_CCtx* dstCCtx,
     {   ZSTD_CCtx_params params = dstCCtx->requestedParams;
         /* Copy only compression parameters related to tables. */
         params.cParams = srcCCtx->appliedParams.cParams;
+        if (windowLog) params.cParams.windowLog = windowLog;
         params.fParams = fParams;
         ZSTD_resetCCtx_internal(dstCCtx, params, pledgedSrcSize,
                                 ZSTDcrp_noMemset, zbuff);
@@ -1045,6 +1056,12 @@ static size_t ZSTD_copyCCtx_internal(ZSTD_CCtx* dstCCtx,
 
     /* copy entropy tables */
     memcpy(dstCCtx->entropy, srcCCtx->entropy, sizeof(ZSTD_entropyCTables_t));
+    /* copy repcodes */
+    {
+        int i;
+        for (i = 0; i < ZSTD_REP_NUM; ++i)
+            dstCCtx->seqStore.rep[i] = srcCCtx->seqStore.rep[i];
+    }
 
     return 0;
 }
@@ -1059,9 +1076,12 @@ size_t ZSTD_copyCCtx(ZSTD_CCtx* dstCCtx, const ZSTD_CCtx* srcCCtx, unsigned long
     ZSTD_frameParameters fParams = { 1 /*content*/, 0 /*checksum*/, 0 /*noDictID*/ };
     ZSTD_buffered_policy_e const zbuff = (ZSTD_buffered_policy_e)(srcCCtx->inBuffSize>0);
     ZSTD_STATIC_ASSERT((U32)ZSTDb_buffered==1);
-    fParams.contentSizeFlag = pledgedSrcSize>0;
+    if (pledgedSrcSize==0) pledgedSrcSize = ZSTD_CONTENTSIZE_UNKNOWN;
+    fParams.contentSizeFlag = (pledgedSrcSize != ZSTD_CONTENTSIZE_UNKNOWN);
 
-    return ZSTD_copyCCtx_internal(dstCCtx, srcCCtx, fParams, pledgedSrcSize, zbuff);
+    return ZSTD_copyCCtx_internal(dstCCtx, srcCCtx,
+                                0 /*windowLog from srcCCtx*/, fParams, pledgedSrcSize,
+                                zbuff);
 }
 
 
@@ -1238,7 +1258,7 @@ static size_t ZSTD_compressLiterals (ZSTD_entropyCTables_t * entropy,
             ostart[4] = (BYTE)(cLitSize >> 10);
             break;
         }
-    default:   /* not possible : lhSize is {3,4,5} */
+    default:  /* not possible : lhSize is {3,4,5} */
         assert(0);
     }
     return lhSize+cLitSize;
@@ -1247,8 +1267,6 @@ static size_t ZSTD_compressLiterals (ZSTD_entropyCTables_t * entropy,
 
 void ZSTD_seqToCodes(const seqStore_t* seqStorePtr)
 {
-    BYTE const LL_deltaCode = 19;
-    BYTE const ML_deltaCode = 36;
     const seqDef* const sequences = seqStorePtr->sequencesStart;
     BYTE* const llCodeTable = seqStorePtr->llCode;
     BYTE* const ofCodeTable = seqStorePtr->ofCode;
@@ -1258,9 +1276,9 @@ void ZSTD_seqToCodes(const seqStore_t* seqStorePtr)
     for (u=0; u<nbSeq; u++) {
         U32 const llv = sequences[u].litLength;
         U32 const mlv = sequences[u].matchLength;
-        llCodeTable[u] = (llv> 63) ? (BYTE)ZSTD_highbit32(llv) + LL_deltaCode : LL_Code[llv];
+        llCodeTable[u] = (BYTE)ZSTD_LLcode(llv);
         ofCodeTable[u] = (BYTE)ZSTD_highbit32(sequences[u].offset);
-        mlCodeTable[u] = (mlv>127) ? (BYTE)ZSTD_highbit32(mlv) + ML_deltaCode : ML_Code[mlv];
+        mlCodeTable[u] = (BYTE)ZSTD_MLcode(mlv);
     }
     if (seqStorePtr->longLengthID==1)
         llCodeTable[seqStorePtr->longLengthPos] = MaxLL;
@@ -1273,7 +1291,8 @@ typedef enum {
     ZSTD_defaultAllowed = 1
 } ZSTD_defaultPolicy_e;
 
-MEM_STATIC symbolEncodingType_e ZSTD_selectEncodingType(
+MEM_STATIC
+symbolEncodingType_e ZSTD_selectEncodingType(
         FSE_repeat* repeatMode, size_t const mostFrequent, size_t nbSeq,
         U32 defaultNormLog, ZSTD_defaultPolicy_e const isDefaultAllowed)
 {
@@ -1281,6 +1300,7 @@ MEM_STATIC symbolEncodingType_e ZSTD_selectEncodingType(
 #define MAX_SEQ_FOR_STATIC_FSE  1000
     ZSTD_STATIC_ASSERT(ZSTD_defaultDisallowed == 0 && ZSTD_defaultAllowed != 0);
     if ((mostFrequent == nbSeq) && (!isDefaultAllowed || nbSeq > 2)) {
+        DEBUGLOG(5, "Selected set_rle");
         /* Prefer set_basic over set_rle when there are 2 or less symbols,
          * since RLE uses 1 byte, but set_basic uses 5-6 bits per symbol.
          * If basic encoding isn't possible, always choose RLE.
@@ -1288,18 +1308,30 @@ MEM_STATIC symbolEncodingType_e ZSTD_selectEncodingType(
         *repeatMode = FSE_repeat_check;
         return set_rle;
     }
-    if (isDefaultAllowed && (*repeatMode == FSE_repeat_valid) && (nbSeq < MAX_SEQ_FOR_STATIC_FSE)) {
+    if ( isDefaultAllowed
+      && (*repeatMode == FSE_repeat_valid) && (nbSeq < MAX_SEQ_FOR_STATIC_FSE)) {
+        DEBUGLOG(5, "Selected set_repeat");
         return set_repeat;
     }
-    if (isDefaultAllowed && ((nbSeq < MIN_SEQ_FOR_DYNAMIC_FSE) || (mostFrequent < (nbSeq >> (defaultNormLog-1))))) {
-        *repeatMode = FSE_repeat_valid;
+    if ( isDefaultAllowed
+      && ((nbSeq < MIN_SEQ_FOR_DYNAMIC_FSE) || (mostFrequent < (nbSeq >> (defaultNormLog-1)))) ) {
+        DEBUGLOG(5, "Selected set_basic");
+        /* The format allows default tables to be repeated, but it isn't useful.
+         * When using simple heuristics to select encoding type, we don't want
+         * to confuse these tables with dictionaries. When running more careful
+         * analysis, we don't need to waste time checking both repeating tables
+         * and default tables.
+         */
+        *repeatMode = FSE_repeat_none;
         return set_basic;
     }
+    DEBUGLOG(5, "Selected set_compressed");
     *repeatMode = FSE_repeat_check;
     return set_compressed;
 }
 
-MEM_STATIC size_t ZSTD_buildCTable(void* dst, size_t dstCapacity,
+MEM_STATIC
+size_t ZSTD_buildCTable(void* dst, size_t dstCapacity,
         FSE_CTable* CTable, U32 FSELog, symbolEncodingType_e type,
         U32* count, U32 max,
         BYTE const* codeTable, size_t nbSeq,
@@ -1317,7 +1349,7 @@ MEM_STATIC size_t ZSTD_buildCTable(void* dst, size_t dstCapacity,
     case set_repeat:
         return 0;
     case set_basic:
-        CHECK_F(FSE_buildCTable_wksp(CTable, defaultNorm, defaultMax, defaultNormLog, workspace, workspaceSize));
+        CHECK_F(FSE_buildCTable_wksp(CTable, defaultNorm, defaultMax, defaultNormLog, workspace, workspaceSize));  /* note : could be pre-calculated */
         return 0;
     case set_compressed: {
         S16 norm[MaxSeq + 1];
@@ -1339,11 +1371,13 @@ MEM_STATIC size_t ZSTD_buildCTable(void* dst, size_t dstCapacity,
     }
 }
 
-MEM_STATIC size_t ZSTD_encodeSequences(void* dst, size_t dstCapacity,
-    FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
-    FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
-    FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
-    seqDef const* sequences, size_t nbSeq, int longOffsets)
+MEM_STATIC
+size_t ZSTD_encodeSequences(
+            void* dst, size_t dstCapacity,
+            FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
+            FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
+            FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
+            seqDef const* sequences, size_t nbSeq, int longOffsets)
 {
     BIT_CStream_t blockStream;
     FSE_CState_t  stateMatchLength;
@@ -1380,8 +1414,12 @@ MEM_STATIC size_t ZSTD_encodeSequences(void* dst, size_t dstCapacity,
             BYTE const ofCode = ofCodeTable[n];
             BYTE const mlCode = mlCodeTable[n];
             U32  const llBits = LL_bits[llCode];
-            U32  const ofBits = ofCode;                                     /* 32b*/  /* 64b*/
+            U32  const ofBits = ofCode;
             U32  const mlBits = ML_bits[mlCode];
+            DEBUGLOG(6, "encoding: litlen:%2u - matchlen:%2u - offCode:%7u",
+                        sequences[n].litLength,
+                        sequences[n].matchLength + MINMATCH,
+                        sequences[n].offset);                               /* 32b*/  /* 64b*/
                                                                             /* (7)*/  /* (7)*/
             FSE_encodeSymbol(&blockStream, &stateOffsetBits, ofCode);       /* 15 */  /* 15 */
             FSE_encodeSymbol(&blockStream, &stateMatchLength, mlCode);      /* 24 */  /* 24 */
@@ -1447,14 +1485,18 @@ MEM_STATIC size_t ZSTD_compressSequences_internal(seqStore_t* seqStorePtr,
                 entropy, cParams->strategy, op, dstCapacity, literals, litSize);
         if (ZSTD_isError(cSize))
           return cSize;
+        assert(cSize <= dstCapacity);
         op += cSize;
     }
 
     /* Sequences Header */
-    if ((oend-op) < 3 /*max nbSeq Size*/ + 1 /*seqHead */) return ERROR(dstSize_tooSmall);
-    if (nbSeq < 0x7F) *op++ = (BYTE)nbSeq;
-    else if (nbSeq < LONGNBSEQ) op[0] = (BYTE)((nbSeq>>8) + 0x80), op[1] = (BYTE)nbSeq, op+=2;
-    else op[0]=0xFF, MEM_writeLE16(op+1, (U16)(nbSeq - LONGNBSEQ)), op+=3;
+    if ((oend-op) < 3 /*max nbSeq Size*/ + 1 /*seqHead*/) return ERROR(dstSize_tooSmall);
+    if (nbSeq < 0x7F)
+        *op++ = (BYTE)nbSeq;
+    else if (nbSeq < LONGNBSEQ)
+        op[0] = (BYTE)((nbSeq>>8) + 0x80), op[1] = (BYTE)nbSeq, op+=2;
+    else
+        op[0]=0xFF, MEM_writeLE16(op+1, (U16)(nbSeq - LONGNBSEQ)), op+=3;
     if (nbSeq==0) return op - ostart;
 
     /* seqHead : flags for FSE encoding type */
@@ -1462,9 +1504,10 @@ MEM_STATIC size_t ZSTD_compressSequences_internal(seqStore_t* seqStorePtr,
 
     /* convert length/distances into codes */
     ZSTD_seqToCodes(seqStorePtr);
-    /* CTable for Literal Lengths */
+    /* build CTable for Literal Lengths */
     {   U32 max = MaxLL;
         size_t const mostFrequent = FSE_countFast_wksp(count, &max, llCodeTable, nbSeq, entropy->workspace);
+        DEBUGLOG(5, "Building LL table");
         LLtype = ZSTD_selectEncodingType(&entropy->litlength_repeatMode, mostFrequent, nbSeq, LL_defaultNormLog, ZSTD_defaultAllowed);
         {   size_t const countSize = ZSTD_buildCTable(op, oend - op, CTable_LitLength, LLFSELog, (symbolEncodingType_e)LLtype,
                     count, max, llCodeTable, nbSeq, LL_defaultNorm, LL_defaultNormLog, MaxLL,
@@ -1472,11 +1515,12 @@ MEM_STATIC size_t ZSTD_compressSequences_internal(seqStore_t* seqStorePtr,
             if (ZSTD_isError(countSize)) return countSize;
             op += countSize;
     }   }
-    /* CTable for Offsets */
+    /* build CTable for Offsets */
     {   U32 max = MaxOff;
         size_t const mostFrequent = FSE_countFast_wksp(count, &max, ofCodeTable, nbSeq, entropy->workspace);
         /* We can only use the basic table if max <= DefaultMaxOff, otherwise the offsets are too large */
-        ZSTD_defaultPolicy_e const defaultPolicy = max <= DefaultMaxOff ? ZSTD_defaultAllowed : ZSTD_defaultDisallowed;
+        ZSTD_defaultPolicy_e const defaultPolicy = (max <= DefaultMaxOff) ? ZSTD_defaultAllowed : ZSTD_defaultDisallowed;
+        DEBUGLOG(5, "Building OF table");
         Offtype = ZSTD_selectEncodingType(&entropy->offcode_repeatMode, mostFrequent, nbSeq, OF_defaultNormLog, defaultPolicy);
         {   size_t const countSize = ZSTD_buildCTable(op, oend - op, CTable_OffsetBits, OffFSELog, (symbolEncodingType_e)Offtype,
                     count, max, ofCodeTable, nbSeq, OF_defaultNorm, OF_defaultNormLog, DefaultMaxOff,
@@ -1484,9 +1528,10 @@ MEM_STATIC size_t ZSTD_compressSequences_internal(seqStore_t* seqStorePtr,
             if (ZSTD_isError(countSize)) return countSize;
             op += countSize;
     }   }
-    /* CTable for MatchLengths */
+    /* build CTable for MatchLengths */
     {   U32 max = MaxML;
         size_t const mostFrequent = FSE_countFast_wksp(count, &max, mlCodeTable, nbSeq, entropy->workspace);
+        DEBUGLOG(5, "Building ML table");
         MLtype = ZSTD_selectEncodingType(&entropy->matchlength_repeatMode, mostFrequent, nbSeq, ML_defaultNormLog, ZSTD_defaultAllowed);
         {   size_t const countSize = ZSTD_buildCTable(op, oend - op, CTable_MatchLength, MLFSELog, (symbolEncodingType_e)MLtype,
                     count, max, mlCodeTable, nbSeq, ML_defaultNorm, ML_defaultNormLog, MaxML,
@@ -1497,13 +1542,15 @@ MEM_STATIC size_t ZSTD_compressSequences_internal(seqStore_t* seqStorePtr,
 
     *seqHead = (BYTE)((LLtype<<6) + (Offtype<<4) + (MLtype<<2));
 
-    {   size_t const streamSize = ZSTD_encodeSequences(op, oend - op,
-                CTable_MatchLength, mlCodeTable,
-                CTable_OffsetBits, ofCodeTable,
-                CTable_LitLength, llCodeTable,
-                sequences, nbSeq, longOffsets);
-        if (ZSTD_isError(streamSize)) return streamSize;
-        op += streamSize;
+    {   size_t const bitstreamSize = ZSTD_encodeSequences(
+                                        op, oend - op,
+                                        CTable_MatchLength, mlCodeTable,
+                                        CTable_OffsetBits, ofCodeTable,
+                                        CTable_LitLength, llCodeTable,
+                                        sequences, nbSeq,
+                                        longOffsets);
+        if (ZSTD_isError(bitstreamSize)) return bitstreamSize;
+        op += bitstreamSize;
     }
 
     return op - ostart;
@@ -1517,27 +1564,33 @@ MEM_STATIC size_t ZSTD_compressSequences(seqStore_t* seqStorePtr,
 {
     size_t const cSize = ZSTD_compressSequences_internal(seqStorePtr, entropy, cParams,
                                                          dst, dstCapacity);
-    size_t const minGain = ZSTD_minGain(srcSize);
-    size_t const maxCSize = srcSize - minGain;
     /* If the srcSize <= dstCapacity, then there is enough space to write a
      * raw uncompressed block. Since we ran out of space, the block must not
      * be compressible, so fall back to a raw uncompressed block.
      */
-    int const uncompressibleError = cSize == ERROR(dstSize_tooSmall) && srcSize <= dstCapacity;
-
+    int const uncompressibleError = (cSize == ERROR(dstSize_tooSmall)) && (srcSize <= dstCapacity);
     if (ZSTD_isError(cSize) && !uncompressibleError)
         return cSize;
+    /* We check that dictionaries have offset codes available for the first
+     * block. After the first block, the offcode table might not have large
+     * enough codes to represent the offsets in the data.
+     */
+    if (entropy->offcode_repeatMode == FSE_repeat_valid)
+        entropy->offcode_repeatMode = FSE_repeat_check;
+
     /* Check compressibility */
-    if (cSize >= maxCSize || uncompressibleError) {
-        entropy->hufCTable_repeatMode = HUF_repeat_none;
-        entropy->offcode_repeatMode = FSE_repeat_none;
-        entropy->matchlength_repeatMode = FSE_repeat_none;
-        entropy->litlength_repeatMode = FSE_repeat_none;
-        return 0;
-    }
+    {   size_t const minGain = ZSTD_minGain(srcSize);  /* note : fixed formula, maybe should depend on compression level, or strategy */
+        size_t const maxCSize = srcSize - minGain;
+        if (cSize >= maxCSize || uncompressibleError) {
+            entropy->hufCTable_repeatMode = HUF_repeat_none;
+            entropy->offcode_repeatMode = FSE_repeat_none;
+            entropy->matchlength_repeatMode = FSE_repeat_none;
+            entropy->litlength_repeatMode = FSE_repeat_none;
+            return 0;  /* block not compressed */
+    }   }
     assert(!ZSTD_isError(cSize));
 
-    /* confirm repcodes */
+    /* block is compressed => confirm repcodes in history */
     { int i; for (i=0; i<ZSTD_REP_NUM; i++) seqStorePtr->rep[i] = seqStorePtr->repToConfirm[i]; }
     return cSize;
 }
@@ -1559,9 +1612,9 @@ ZSTD_blockCompressor ZSTD_selectBlockCompressor(ZSTD_strategy strat, int extDict
           ZSTD_compressBlock_btopt_extDict, ZSTD_compressBlock_btultra_extDict }
     };
     ZSTD_STATIC_ASSERT((unsigned)ZSTD_fast == 1);
+
     assert((U32)strat >= (U32)ZSTD_fast);
     assert((U32)strat <= (U32)ZSTD_btultra);
-
     return blockCompressor[extDict!=0][(U32)strat];
 }
 
@@ -1572,30 +1625,38 @@ static void ZSTD_storeLastLiterals(seqStore_t* seqStorePtr,
     seqStorePtr->lit += lastLLSize;
 }
 
+static void ZSTD_resetSeqStore(seqStore_t* ssPtr)
+{
+    ssPtr->lit = ssPtr->litStart;
+    ssPtr->sequences = ssPtr->sequencesStart;
+    ssPtr->longLengthID = 0;
+}
+
 static size_t ZSTD_compressBlock_internal(ZSTD_CCtx* zc, void* dst, size_t dstCapacity, const void* src, size_t srcSize)
 {
-    const BYTE* const base = zc->base;
-    const BYTE* const istart = (const BYTE*)src;
-    const U32 current = (U32)(istart-base);
-    size_t lastLLSize;
-    const BYTE* anchor;
-    U32 const extDict = zc->lowLimit < zc->dictLimit;
-    const ZSTD_blockCompressor blockCompressor =
-        zc->appliedParams.ldmParams.enableLdm
-            ? (extDict ? ZSTD_compressBlock_ldm_extDict : ZSTD_compressBlock_ldm)
-            : ZSTD_selectBlockCompressor(zc->appliedParams.cParams.strategy, extDict);
-
-    if (srcSize < MIN_CBLOCK_SIZE+ZSTD_blockHeaderSize+1) return 0;   /* don't even attempt compression below a certain srcSize */
+    DEBUGLOG(5, "ZSTD_compressBlock_internal : dstCapacity = %u", (U32)dstCapacity);
+    if (srcSize < MIN_CBLOCK_SIZE+ZSTD_blockHeaderSize+1)
+        return 0;   /* don't even attempt compression below a certain srcSize */
     ZSTD_resetSeqStore(&(zc->seqStore));
-    if (current > zc->nextToUpdate + 384)
-        zc->nextToUpdate = current - MIN(192, (U32)(current - zc->nextToUpdate - 384));   /* limited update after finding a very long match */
-
-    lastLLSize = blockCompressor(zc, src, srcSize);
-
-    /* Last literals */
-    anchor = (const BYTE*)src + srcSize - lastLLSize;
-    ZSTD_storeLastLiterals(&zc->seqStore, anchor, lastLLSize);
 
+    /* limited update after a very long match */
+    {   const BYTE* const base = zc->base;
+        const BYTE* const istart = (const BYTE*)src;
+        const U32 current = (U32)(istart-base);
+        if (current > zc->nextToUpdate + 384)
+            zc->nextToUpdate = current - MIN(192, (U32)(current - zc->nextToUpdate - 384));
+    }
+    /* find and store sequences */
+    {   U32 const extDict = zc->lowLimit < zc->dictLimit;
+        const ZSTD_blockCompressor blockCompressor =
+            zc->appliedParams.ldmParams.enableLdm
+                ? (extDict ? ZSTD_compressBlock_ldm_extDict : ZSTD_compressBlock_ldm)
+                : ZSTD_selectBlockCompressor(zc->appliedParams.cParams.strategy, extDict);
+        size_t const lastLLSize = blockCompressor(zc, src, srcSize);
+        const BYTE* const anchor = (const BYTE*)src + srcSize - lastLLSize;
+        ZSTD_storeLastLiterals(&zc->seqStore, anchor, lastLLSize);
+    }
+    /* encode */
     return ZSTD_compressSequences(&zc->seqStore, zc->entropy, &zc->appliedParams.cParams, dst, dstCapacity, srcSize);
 }
 
@@ -1618,13 +1679,14 @@ static size_t ZSTD_compress_frameChunk (ZSTD_CCtx* cctx,
     BYTE* const ostart = (BYTE*)dst;
     BYTE* op = ostart;
     U32 const maxDist = (U32)1 << cctx->appliedParams.cParams.windowLog;
+    assert(cctx->appliedParams.cParams.windowLog <= 31);
 
+    DEBUGLOG(5, "ZSTD_compress_frameChunk (blockSize=%u)", (U32)blockSize);
     if (cctx->appliedParams.fParams.checksumFlag && srcSize)
         XXH64_update(&cctx->xxhState, src, srcSize);
 
     while (remaining) {
         U32 const lastBlock = lastFrameChunk & (blockSize >= remaining);
-        size_t cSize;
 
         if (dstCapacity < ZSTD_blockHeaderSize + MIN_CBLOCK_SIZE)
             return ERROR(dstSize_tooSmall);   /* not enough space to store compressed block */
@@ -1666,34 +1728,39 @@ static size_t ZSTD_compress_frameChunk (ZSTD_CCtx* cctx,
             else cctx->nextToUpdate -= correction;
             DEBUGLOG(4, "Correction of 0x%x bytes to lowLimit=0x%x\n", correction, cctx->lowLimit);
         }
-
+        /* enforce maxDist */
         if ((U32)(ip+blockSize - cctx->base) > cctx->loadedDictEnd + maxDist) {
-            /* enforce maxDist */
             U32 const newLowLimit = (U32)(ip+blockSize - cctx->base) - maxDist;
             if (cctx->lowLimit < newLowLimit) cctx->lowLimit = newLowLimit;
             if (cctx->dictLimit < cctx->lowLimit) cctx->dictLimit = cctx->lowLimit;
         }
 
-        cSize = ZSTD_compressBlock_internal(cctx, op+ZSTD_blockHeaderSize, dstCapacity-ZSTD_blockHeaderSize, ip, blockSize);
-        if (ZSTD_isError(cSize)) return cSize;
-
-        if (cSize == 0) {  /* block is not compressible */
-            U32 const cBlockHeader24 = lastBlock + (((U32)bt_raw)<<1) + (U32)(blockSize << 3);
-            if (blockSize + ZSTD_blockHeaderSize > dstCapacity) return ERROR(dstSize_tooSmall);
-            MEM_writeLE32(op, cBlockHeader24);   /* no pb, 4th byte will be overwritten */
-            memcpy(op + ZSTD_blockHeaderSize, ip, blockSize);
-            cSize = ZSTD_blockHeaderSize+blockSize;
-        } else {
-            U32 const cBlockHeader24 = lastBlock + (((U32)bt_compressed)<<1) + (U32)(cSize << 3);
-            MEM_writeLE24(op, cBlockHeader24);
-            cSize += ZSTD_blockHeaderSize;
-        }
+        {   size_t cSize = ZSTD_compressBlock_internal(cctx,
+                                op+ZSTD_blockHeaderSize, dstCapacity-ZSTD_blockHeaderSize,
+                                ip, blockSize);
+            if (ZSTD_isError(cSize)) return cSize;
+
+            if (cSize == 0) {  /* block is not compressible */
+                U32 const cBlockHeader24 = lastBlock + (((U32)bt_raw)<<1) + (U32)(blockSize << 3);
+                if (blockSize + ZSTD_blockHeaderSize > dstCapacity) return ERROR(dstSize_tooSmall);
+                MEM_writeLE32(op, cBlockHeader24);   /* 4th byte will be overwritten */
+                memcpy(op + ZSTD_blockHeaderSize, ip, blockSize);
+                cSize = ZSTD_blockHeaderSize + blockSize;
+            } else {
+                U32 const cBlockHeader24 = lastBlock + (((U32)bt_compressed)<<1) + (U32)(cSize << 3);
+                MEM_writeLE24(op, cBlockHeader24);
+                cSize += ZSTD_blockHeaderSize;
+            }
 
-        remaining -= blockSize;
-        dstCapacity -= cSize;
-        ip += blockSize;
-        op += cSize;
-    }
+            ip += blockSize;
+            assert(remaining >= blockSize);
+            remaining -= blockSize;
+            op += cSize;
+            assert(dstCapacity >= cSize);
+            dstCapacity -= cSize;
+            DEBUGLOG(5, "ZSTD_compress_frameChunk: adding a block of size %u",
+                        (U32)cSize);
+    }   }
 
     if (lastFrameChunk && (op>ostart)) cctx->stage = ZSTDcs_ending;
     return op-ostart;
@@ -1719,7 +1786,6 @@ static size_t ZSTD_writeFrameHeader(void* dst, size_t dstCapacity,
                 !params.fParams.noDictIDFlag, dictID,  dictIDSizeCode);
 
     if (params.format == ZSTD_f_zstd1) {
-        DEBUGLOG(4, "writing zstd magic number");
         MEM_writeLE32(dst, ZSTD_MAGICNUMBER);
         pos = 4;
     }
@@ -1753,8 +1819,7 @@ static size_t ZSTD_compressContinue_internal (ZSTD_CCtx* cctx,
     const BYTE* const ip = (const BYTE*) src;
     size_t fhSize = 0;
 
-    DEBUGLOG(5, "ZSTD_compressContinue_internal");
-    DEBUGLOG(5, "stage: %u", cctx->stage);
+    DEBUGLOG(5, "ZSTD_compressContinue_internal, stage: %u", cctx->stage);
     if (cctx->stage==ZSTDcs_created) return ERROR(stage_wrong);   /* missing init (ZSTD_compressBegin) */
 
     if (frame && (cctx->stage==ZSTDcs_init)) {
@@ -1766,17 +1831,21 @@ static size_t ZSTD_compressContinue_internal (ZSTD_CCtx* cctx,
         cctx->stage = ZSTDcs_ongoing;
     }
 
+    if (!srcSize) return fhSize;  /* do not generate an empty block if no input */
+
     /* Check if blocks follow each other */
     if (src != cctx->nextSrc) {
         /* not contiguous */
-        ptrdiff_t const delta = cctx->nextSrc - ip;
+        size_t const distanceFromBase = (size_t)(cctx->nextSrc - cctx->base);
         cctx->lowLimit = cctx->dictLimit;
-        cctx->dictLimit = (U32)(cctx->nextSrc - cctx->base);
+        assert(distanceFromBase == (size_t)(U32)distanceFromBase);  /* should never overflow */
+        cctx->dictLimit = (U32)distanceFromBase;
         cctx->dictBase = cctx->base;
-        cctx->base -= delta;
+        cctx->base = ip - distanceFromBase;
         cctx->nextToUpdate = cctx->dictLimit;
         if (cctx->dictLimit - cctx->lowLimit < HASH_READ_SIZE) cctx->lowLimit = cctx->dictLimit;   /* too small extDict */
     }
+    cctx->nextSrc = ip + srcSize;
 
     /* if input and dictionary overlap : reduce dictionary (area presumed modified by input) */
     if ((ip+srcSize > cctx->dictBase + cctx->lowLimit) & (ip < cctx->dictBase + cctx->dictLimit)) {
@@ -1785,17 +1854,14 @@ static size_t ZSTD_compressContinue_internal (ZSTD_CCtx* cctx,
         cctx->lowLimit = lowLimitMax;
     }
 
-    cctx->nextSrc = ip + srcSize;
-
-    if (srcSize) {
-        size_t const cSize = frame ?
+    DEBUGLOG(5, "ZSTD_compressContinue_internal (blockSize=%u)", (U32)cctx->blockSize);
+    {   size_t const cSize = frame ?
                              ZSTD_compress_frameChunk (cctx, dst, dstCapacity, src, srcSize, lastFrameChunk) :
                              ZSTD_compressBlock_internal (cctx, dst, dstCapacity, src, srcSize);
         if (ZSTD_isError(cSize)) return cSize;
         cctx->consumedSrcSize += srcSize;
         return cSize + fhSize;
-    } else
-        return fhSize;
+    }
 }
 
 size_t ZSTD_compressContinue (ZSTD_CCtx* cctx,
@@ -1832,7 +1898,7 @@ static size_t ZSTD_loadDictionaryContent(ZSTD_CCtx* zc, const void* src, size_t
     zc->lowLimit = zc->dictLimit;
     zc->dictLimit = (U32)(zc->nextSrc - zc->base);
     zc->dictBase = zc->base;
-    zc->base += ip - zc->nextSrc;
+    zc->base = ip - zc->dictLimit;
     zc->nextToUpdate = zc->dictLimit;
     zc->loadedDictEnd = zc->appliedParams.forceWindow ? 0 : (U32)(iend - zc->base);
 
@@ -1983,7 +2049,7 @@ static size_t ZSTD_compress_insertDictionary(ZSTD_CCtx* cctx,
                                        const void* dict, size_t dictSize,
                                              ZSTD_dictMode_e dictMode)
 {
-    DEBUGLOG(5, "ZSTD_compress_insertDictionary");
+    DEBUGLOG(4, "ZSTD_compress_insertDictionary (dictSize=%u)", (U32)dictSize);
     if ((dict==NULL) || (dictSize<=8)) return 0;
 
     /* dict restricted modes */
@@ -1992,7 +2058,7 @@ static size_t ZSTD_compress_insertDictionary(ZSTD_CCtx* cctx,
 
     if (MEM_readLE32(dict) != ZSTD_MAGIC_DICTIONARY) {
         if (dictMode == ZSTD_dm_auto) {
-            DEBUGLOG(5, "raw content dictionary detected");
+            DEBUGLOG(4, "raw content dictionary detected");
             return ZSTD_loadDictionaryContent(cctx, dict, dictSize);
         }
         if (dictMode == ZSTD_dm_fullDict)
@@ -2006,21 +2072,22 @@ static size_t ZSTD_compress_insertDictionary(ZSTD_CCtx* cctx,
 
 /*! ZSTD_compressBegin_internal() :
  * @return : 0, or an error code */
-static size_t ZSTD_compressBegin_internal(ZSTD_CCtx* cctx,
+size_t ZSTD_compressBegin_internal(ZSTD_CCtx* cctx,
                              const void* dict, size_t dictSize,
                              ZSTD_dictMode_e dictMode,
                              const ZSTD_CDict* cdict,
-                                   ZSTD_CCtx_params params, U64 pledgedSrcSize,
-                                   ZSTD_buffered_policy_e zbuff)
+                             ZSTD_CCtx_params params, U64 pledgedSrcSize,
+                             ZSTD_buffered_policy_e zbuff)
 {
-    DEBUGLOG(4, "ZSTD_compressBegin_internal");
+    DEBUGLOG(4, "ZSTD_compressBegin_internal: wlog=%u", params.cParams.windowLog);
     /* params are supposed to be fully validated at this point */
     assert(!ZSTD_isError(ZSTD_checkCParams(params.cParams)));
     assert(!((dict) && (cdict)));  /* either dict or cdict, not both */
 
     if (cdict && cdict->dictContentSize>0) {
+        cctx->requestedParams = params;
         return ZSTD_copyCCtx_internal(cctx, cdict->refContext,
-                                      params.fParams, pledgedSrcSize,
+                                      params.cParams.windowLog, params.fParams, pledgedSrcSize,
                                       zbuff);
     }
 
@@ -2029,16 +2096,19 @@ static size_t ZSTD_compressBegin_internal(ZSTD_CCtx* cctx,
     return ZSTD_compress_insertDictionary(cctx, dict, dictSize, dictMode);
 }
 
-size_t ZSTD_compressBegin_advanced_internal(
-                                    ZSTD_CCtx* cctx,
+size_t ZSTD_compressBegin_advanced_internal(ZSTD_CCtx* cctx,
                                     const void* dict, size_t dictSize,
                                     ZSTD_dictMode_e dictMode,
+                                    const ZSTD_CDict* cdict,
                                     ZSTD_CCtx_params params,
                                     unsigned long long pledgedSrcSize)
 {
+    DEBUGLOG(4, "ZSTD_compressBegin_advanced_internal: wlog=%u", params.cParams.windowLog);
     /* compression parameters verification and optimization */
     CHECK_F( ZSTD_checkCParams(params.cParams) );
-    return ZSTD_compressBegin_internal(cctx, dict, dictSize, dictMode, NULL,
+    return ZSTD_compressBegin_internal(cctx,
+                                       dict, dictSize, dictMode,
+                                       cdict,
                                        params, pledgedSrcSize,
                                        ZSTDb_not_buffered);
 }
@@ -2051,9 +2121,10 @@ size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx,
 {
     ZSTD_CCtx_params const cctxParams =
             ZSTD_assignParamsToCCtxParams(cctx->requestedParams, params);
-    return ZSTD_compressBegin_advanced_internal(cctx, dict, dictSize, ZSTD_dm_auto,
-                                                cctxParams,
-                                                pledgedSrcSize);
+    return ZSTD_compressBegin_advanced_internal(cctx,
+                                            dict, dictSize, ZSTD_dm_auto,
+                                            NULL /*cdict*/,
+                                            cctxParams, pledgedSrcSize);
 }
 
 size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel)
@@ -2061,8 +2132,9 @@ size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t di
     ZSTD_parameters const params = ZSTD_getParams(compressionLevel, 0, dictSize);
     ZSTD_CCtx_params const cctxParams =
             ZSTD_assignParamsToCCtxParams(cctx->requestedParams, params);
+    DEBUGLOG(4, "ZSTD_compressBegin_usingDict");
     return ZSTD_compressBegin_internal(cctx, dict, dictSize, ZSTD_dm_auto, NULL,
-                                       cctxParams, 0, ZSTDb_not_buffered);
+                                       cctxParams, ZSTD_CONTENTSIZE_UNKNOWN, ZSTDb_not_buffered);
 }
 
 size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel)
@@ -2143,6 +2215,7 @@ static size_t ZSTD_compress_internal (ZSTD_CCtx* cctx,
 {
     ZSTD_CCtx_params const cctxParams =
             ZSTD_assignParamsToCCtxParams(cctx->requestedParams, params);
+    DEBUGLOG(4, "ZSTD_compress_internal");
     return ZSTD_compress_advanced_internal(cctx,
                                           dst, dstCapacity,
                                           src, srcSize,
@@ -2156,6 +2229,7 @@ size_t ZSTD_compress_advanced (ZSTD_CCtx* ctx,
                          const void* dict,size_t dictSize,
                                ZSTD_parameters params)
 {
+    DEBUGLOG(4, "ZSTD_compress_advanced");
     CHECK_F(ZSTD_checkCParams(params.cParams));
     return ZSTD_compress_internal(ctx, dst, dstCapacity, src, srcSize, dict, dictSize, params);
 }
@@ -2168,6 +2242,7 @@ size_t ZSTD_compress_advanced_internal(
         const void* dict,size_t dictSize,
         ZSTD_CCtx_params params)
 {
+    DEBUGLOG(4, "ZSTD_compress_advanced_internal");
     CHECK_F( ZSTD_compressBegin_internal(cctx, dict, dictSize, ZSTD_dm_auto, NULL,
                                          params, srcSize, ZSTDb_not_buffered) );
     return ZSTD_compressEnd(cctx, dst, dstCapacity, src, srcSize);
@@ -2176,8 +2251,10 @@ size_t ZSTD_compress_advanced_internal(
 size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize,
                                const void* dict, size_t dictSize, int compressionLevel)
 {
-    ZSTD_parameters params = ZSTD_getParams(compressionLevel, srcSize, dict ? dictSize : 0);
+    ZSTD_parameters params = ZSTD_getParams(compressionLevel, srcSize ? srcSize : 1, dict ? dictSize : 0);
     params.fParams.contentSizeFlag = 1;
+    DEBUGLOG(4, "ZSTD_compress_usingDict (level=%i, srcSize=%u, dictSize=%u)",
+                compressionLevel, (U32)srcSize, (U32)dictSize);
     return ZSTD_compress_internal(ctx, dst, dstCapacity, src, srcSize, dict, dictSize, params);
 }
 
@@ -2234,7 +2311,7 @@ static size_t ZSTD_initCDict_internal(
                     ZSTD_dictMode_e dictMode,
                     ZSTD_compressionParameters cParams)
 {
-    DEBUGLOG(5, "ZSTD_initCDict_internal, mode %u", (U32)dictMode);
+    DEBUGLOG(3, "ZSTD_initCDict_internal, mode %u", (U32)dictMode);
     if ((dictLoadMethod == ZSTD_dlm_byRef) || (!dictBuffer) || (!dictSize)) {
         cdict->dictBuffer = NULL;
         cdict->dictContent = dictBuffer;
@@ -2264,7 +2341,7 @@ ZSTD_CDict* ZSTD_createCDict_advanced(const void* dictBuffer, size_t dictSize,
                                       ZSTD_dictMode_e dictMode,
                                       ZSTD_compressionParameters cParams, ZSTD_customMem customMem)
 {
-    DEBUGLOG(5, "ZSTD_createCDict_advanced, mode %u", (U32)dictMode);
+    DEBUGLOG(3, "ZSTD_createCDict_advanced, mode %u", (U32)dictMode);
     if (!customMem.customAlloc ^ !customMem.customFree) return NULL;
 
     {   ZSTD_CDict* const cdict = (ZSTD_CDict*)ZSTD_malloc(sizeof(ZSTD_CDict), customMem);
@@ -2339,9 +2416,9 @@ ZSTD_CDict* ZSTD_initStaticCDict(void* workspace, size_t workspaceSize,
                             + cctxSize;
     ZSTD_CDict* const cdict = (ZSTD_CDict*) workspace;
     void* ptr;
-    DEBUGLOG(5, "(size_t)workspace & 7 : %u", (U32)(size_t)workspace & 7);
+    DEBUGLOG(4, "(size_t)workspace & 7 : %u", (U32)(size_t)workspace & 7);
     if ((size_t)workspace & 7) return NULL;  /* 8-aligned */
-    DEBUGLOG(5, "(workspaceSize < neededSize) : (%u < %u) => %u",
+    DEBUGLOG(4, "(workspaceSize < neededSize) : (%u < %u) => %u",
         (U32)workspaceSize, (U32)neededSize, (U32)(workspaceSize < neededSize));
     if (workspaceSize < neededSize) return NULL;
 
@@ -2373,11 +2450,11 @@ size_t ZSTD_compressBegin_usingCDict_advanced(
     ZSTD_CCtx* const cctx, const ZSTD_CDict* const cdict,
     ZSTD_frameParameters const fParams, unsigned long long const pledgedSrcSize)
 {
+    DEBUGLOG(4, "ZSTD_compressBegin_usingCDict_advanced");
     if (cdict==NULL) return ERROR(dictionary_wrong);
     {   ZSTD_CCtx_params params = cctx->requestedParams;
         params.cParams = ZSTD_getCParamsFromCDict(cdict);
         params.fParams = fParams;
-        DEBUGLOG(5, "ZSTD_compressBegin_usingCDict_advanced");
         return ZSTD_compressBegin_internal(cctx,
                                            NULL, 0, ZSTD_dm_auto,
                                            cdict,
@@ -2392,7 +2469,7 @@ size_t ZSTD_compressBegin_usingCDict_advanced(
 size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict)
 {
     ZSTD_frameParameters const fParams = { 0 /*content*/, 0 /*checksum*/, 0 /*noDictID*/ };
-    DEBUGLOG(5, "ZSTD_compressBegin_usingCDict : dictIDFlag == %u", !fParams.noDictIDFlag);
+    DEBUGLOG(4, "ZSTD_compressBegin_usingCDict : dictIDFlag == %u", !fParams.noDictIDFlag);
     return ZSTD_compressBegin_usingCDict_advanced(cctx, cdict, fParams, 0);
 }
 
@@ -2427,6 +2504,7 @@ size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
 
 ZSTD_CStream* ZSTD_createCStream(void)
 {
+    DEBUGLOG(3, "ZSTD_createCStream");
     return ZSTD_createCStream_advanced(ZSTD_defaultCMem);
 }
 
@@ -2457,9 +2535,9 @@ size_t ZSTD_CStreamOutSize(void)
 }
 
 static size_t ZSTD_resetCStream_internal(ZSTD_CStream* zcs,
-                    const void* dict, size_t dictSize, ZSTD_dictMode_e dictMode,
-                    const ZSTD_CDict* cdict,
-                    const ZSTD_CCtx_params params, unsigned long long pledgedSrcSize)
+                    const void* const dict, size_t const dictSize, ZSTD_dictMode_e const dictMode,
+                    const ZSTD_CDict* const cdict,
+                    ZSTD_CCtx_params const params, unsigned long long const pledgedSrcSize)
 {
     DEBUGLOG(4, "ZSTD_resetCStream_internal");
     /* params are supposed to be fully validated at this point */
@@ -2467,31 +2545,35 @@ static size_t ZSTD_resetCStream_internal(ZSTD_CStream* zcs,
     assert(!((dict) && (cdict)));  /* either dict or cdict, not both */
 
     CHECK_F( ZSTD_compressBegin_internal(zcs,
-                                        dict, dictSize, dictMode,
-                                        cdict,
-                                        params, pledgedSrcSize,
-                                        ZSTDb_buffered) );
+                                         dict, dictSize, dictMode,
+                                         cdict,
+                                         params, pledgedSrcSize,
+                                         ZSTDb_buffered) );
 
     zcs->inToCompress = 0;
     zcs->inBuffPos = 0;
-    zcs->inBuffTarget = zcs->blockSize;
+    zcs->inBuffTarget = zcs->blockSize
+                      + (zcs->blockSize == pledgedSrcSize);   /* for small input: avoid automatic flush on reaching end of block, since it would require to add a 3-bytes null block to end frame */
     zcs->outBuffContentSize = zcs->outBuffFlushedSize = 0;
     zcs->streamStage = zcss_load;
     zcs->frameEnded = 0;
     return 0;   /* ready to go */
 }
 
+/* ZSTD_resetCStream():
+ * pledgedSrcSize == 0 means "unknown" */
 size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize)
 {
     ZSTD_CCtx_params params = zcs->requestedParams;
-    params.fParams.contentSizeFlag = (pledgedSrcSize > 0);
+    DEBUGLOG(4, "ZSTD_resetCStream: pledgedSrcSize = %u", (U32)pledgedSrcSize);
+    if (pledgedSrcSize==0) pledgedSrcSize = ZSTD_CONTENTSIZE_UNKNOWN;
+    params.fParams.contentSizeFlag = 1;
     params.cParams = ZSTD_getCParamsFromCCtxParams(params, pledgedSrcSize, 0);
-    DEBUGLOG(4, "ZSTD_resetCStream");
     return ZSTD_resetCStream_internal(zcs, NULL, 0, ZSTD_dm_auto, zcs->cdict, params, pledgedSrcSize);
 }
 
 /*! ZSTD_initCStream_internal() :
- *  Note : not static, but hidden (not exposed). Used by zstdmt_compress.c
+ *  Note : for lib/compress only. Used by zstdmt_compress.c.
  *  Assumption 1 : params are valid
  *  Assumption 2 : either dict, or cdict, is defined, not both */
 size_t ZSTD_initCStream_internal(ZSTD_CStream* zcs,
@@ -2503,7 +2585,7 @@ size_t ZSTD_initCStream_internal(ZSTD_CStream* zcs,
     assert(!((dict) && (cdict)));  /* either dict or cdict, not both */
 
     if (dict && dictSize >= 8) {
-        DEBUGLOG(5, "loading dictionary of size %u", (U32)dictSize);
+        DEBUGLOG(4, "loading dictionary of size %u", (U32)dictSize);
         if (zcs->staticSize) {   /* static CCtx : never uses malloc */
             /* incompatible with internal cdict creation */
             return ERROR(memory_allocation);
@@ -2516,14 +2598,14 @@ size_t ZSTD_initCStream_internal(ZSTD_CStream* zcs,
         if (zcs->cdictLocal == NULL) return ERROR(memory_allocation);
     } else {
         if (cdict) {
-            params.cParams = ZSTD_getCParamsFromCDict(cdict);  /* cParams are enforced from cdict */
+            params.cParams = ZSTD_getCParamsFromCDict(cdict);  /* cParams are enforced from cdict; it includes windowLog */
         }
         ZSTD_freeCDict(zcs->cdictLocal);
         zcs->cdictLocal = NULL;
         zcs->cdict = cdict;
     }
 
-    params.compressionLevel = ZSTD_CLEVEL_CUSTOM;
+    params.compressionLevel = ZSTD_CLEVEL_CUSTOM; /* enforce usage of cParams, instead of a dynamic derivation from cLevel (but does that happen ?) */
     zcs->requestedParams = params;
 
     return ZSTD_resetCStream_internal(zcs, NULL, 0, ZSTD_dm_auto, zcs->cdict, params, pledgedSrcSize);
@@ -2535,8 +2617,9 @@ size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs,
                                             const ZSTD_CDict* cdict,
                                             ZSTD_frameParameters fParams,
                                             unsigned long long pledgedSrcSize)
-{   /* cannot handle NULL cdict (does not know what to do) */
-    if (!cdict) return ERROR(dictionary_wrong);
+{
+    DEBUGLOG(4, "ZSTD_initCStream_usingCDict_advanced");
+    if (!cdict) return ERROR(dictionary_wrong); /* cannot handle NULL cdict (does not know what to do) */
     {   ZSTD_CCtx_params params = zcs->requestedParams;
         params.cParams = ZSTD_getCParamsFromCDict(cdict);
         params.fParams = fParams;
@@ -2549,18 +2632,25 @@ size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs,
 /* note : cdict must outlive compression session */
 size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict)
 {
-    ZSTD_frameParameters const fParams = { 0 /* contentSize */, 0 /* checksum */, 0 /* hideDictID */ };
-    return ZSTD_initCStream_usingCDict_advanced(zcs, cdict, fParams, 0);  /* note : will check that cdict != NULL */
+    ZSTD_frameParameters const fParams = { 0 /* contentSizeFlag */, 0 /* checksum */, 0 /* hideDictID */ };
+    DEBUGLOG(4, "ZSTD_initCStream_usingCDict");
+    return ZSTD_initCStream_usingCDict_advanced(zcs, cdict, fParams, ZSTD_CONTENTSIZE_UNKNOWN);  /* note : will check that cdict != NULL */
 }
 
+/* ZSTD_initCStream_advanced() :
+ * pledgedSrcSize must be correct.
+ * if srcSize is not known at init time, use value ZSTD_CONTENTSIZE_UNKNOWN.
+ * dict is loaded with default parameters ZSTD_dm_auto and ZSTD_dlm_byCopy. */
 size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs,
                                  const void* dict, size_t dictSize,
                                  ZSTD_parameters params, unsigned long long pledgedSrcSize)
 {
-    ZSTD_CCtx_params const cctxParams =
-            ZSTD_assignParamsToCCtxParams(zcs->requestedParams, params);
+    ZSTD_CCtx_params const cctxParams = ZSTD_assignParamsToCCtxParams(zcs->requestedParams, params);
+    DEBUGLOG(4, "ZSTD_initCStream_advanced: pledgedSrcSize=%u, flag=%u",
+                (U32)pledgedSrcSize, params.fParams.contentSizeFlag);
     CHECK_F( ZSTD_checkCParams(params.cParams) );
-    return ZSTD_initCStream_internal(zcs, dict, dictSize, NULL, cctxParams, pledgedSrcSize);
+    if ((pledgedSrcSize==0) && (params.fParams.contentSizeFlag==0)) pledgedSrcSize = ZSTD_CONTENTSIZE_UNKNOWN;  /* for compatibility with older programs relying on this behavior. Users should now specify ZSTD_CONTENTSIZE_UNKNOWN. This line will be removed in the future. */
+    return ZSTD_initCStream_internal(zcs, dict, dictSize, NULL /*cdict*/, cctxParams, pledgedSrcSize);
 }
 
 size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel)
@@ -2568,21 +2658,21 @@ size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t di
     ZSTD_parameters const params = ZSTD_getParams(compressionLevel, 0, dictSize);
     ZSTD_CCtx_params const cctxParams =
             ZSTD_assignParamsToCCtxParams(zcs->requestedParams, params);
-    return ZSTD_initCStream_internal(zcs, dict, dictSize, NULL, cctxParams, 0);
+    return ZSTD_initCStream_internal(zcs, dict, dictSize, NULL, cctxParams, ZSTD_CONTENTSIZE_UNKNOWN);
 }
 
-size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize)
+size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pss)
 {
-    ZSTD_CCtx_params cctxParams;
+    U64 const pledgedSrcSize = (pss==0) ? ZSTD_CONTENTSIZE_UNKNOWN : pss;  /* temporary : 0 interpreted as "unknown" during transition period. Users willing to specify "unknown" **must** use ZSTD_CONTENTSIZE_UNKNOWN. `0` will be interpreted as "empty" in the future */
     ZSTD_parameters const params = ZSTD_getParams(compressionLevel, pledgedSrcSize, 0);
-    cctxParams = ZSTD_assignParamsToCCtxParams(zcs->requestedParams, params);
-    cctxParams.fParams.contentSizeFlag = (pledgedSrcSize>0);
+    ZSTD_CCtx_params const cctxParams = ZSTD_assignParamsToCCtxParams(zcs->requestedParams, params);
     return ZSTD_initCStream_internal(zcs, NULL, 0, NULL, cctxParams, pledgedSrcSize);
 }
 
 size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel)
 {
-    return ZSTD_initCStream_srcSize(zcs, compressionLevel, 0);
+    DEBUGLOG(4, "ZSTD_initCStream");
+    return ZSTD_initCStream_srcSize(zcs, compressionLevel, ZSTD_CONTENTSIZE_UNKNOWN);
 }
 
 /*======   Compression   ======*/
@@ -2615,9 +2705,9 @@ size_t ZSTD_compressStream_generic(ZSTD_CStream* zcs,
     /* check expectations */
     DEBUGLOG(5, "ZSTD_compressStream_generic, flush=%u", (U32)flushMode);
     assert(zcs->inBuff != NULL);
-    assert(zcs->inBuffSize>0);
-    assert(zcs->outBuff!= NULL);
-    assert(zcs->outBuffSize>0);
+    assert(zcs->inBuffSize > 0);
+    assert(zcs->outBuff !=  NULL);
+    assert(zcs->outBuffSize > 0);
     assert(output->pos <= output->size);
     assert(input->pos <= input->size);
 
@@ -2757,7 +2847,7 @@ size_t ZSTD_compress_generic (ZSTD_CCtx* cctx,
                               ZSTD_inBuffer* input,
                               ZSTD_EndDirective endOp)
 {
-    DEBUGLOG(5, "ZSTD_compress_generic");
+    DEBUGLOG(5, "ZSTD_compress_generic, endOp=%u ", (U32)endOp);
     /* check conditions */
     if (output->pos > output->size) return ERROR(GENERIC);
     if (input->pos  > input->size)  return ERROR(GENERIC);
@@ -2765,42 +2855,47 @@ size_t ZSTD_compress_generic (ZSTD_CCtx* cctx,
 
     /* transparent initialization stage */
     if (cctx->streamStage == zcss_init) {
-        ZSTD_prefixDict const prefixDict = cctx->prefixDict;
         ZSTD_CCtx_params params = cctx->requestedParams;
-        params.cParams = ZSTD_getCParamsFromCCtxParams(
-                cctx->requestedParams, cctx->pledgedSrcSizePlusOne-1, 0 /*dictSize*/);
+        ZSTD_prefixDict const prefixDict = cctx->prefixDict;
         memset(&cctx->prefixDict, 0, sizeof(cctx->prefixDict));  /* single usage */
         assert(prefixDict.dict==NULL || cctx->cdict==NULL);   /* only one can be set */
         DEBUGLOG(4, "ZSTD_compress_generic : transparent init stage");
+        if (endOp == ZSTD_e_end) cctx->pledgedSrcSizePlusOne = input->size + 1;  /* auto-fix pledgedSrcSize */
+        params.cParams = ZSTD_getCParamsFromCCtxParams(
+                cctx->requestedParams, cctx->pledgedSrcSizePlusOne-1, 0 /*dictSize*/);
 
 #ifdef ZSTD_MULTITHREAD
+        if ((cctx->pledgedSrcSizePlusOne-1) <= ZSTDMT_JOBSIZE_MIN)
+            params.nbThreads = 1; /* do not invoke multi-threading when src size is too small */
         if (params.nbThreads > 1) {
-            if (cctx->mtctx == NULL || cctx->appliedParams.nbThreads != params.nbThreads) {
+            if (cctx->mtctx == NULL || (params.nbThreads != ZSTDMT_getNbThreads(cctx->mtctx))) {
+                DEBUGLOG(4, "ZSTD_compress_generic: creating new mtctx for nbThreads=%u (previous: %u)",
+                            params.nbThreads, ZSTDMT_getNbThreads(cctx->mtctx));
                 ZSTDMT_freeCCtx(cctx->mtctx);
                 cctx->mtctx = ZSTDMT_createCCtx_advanced(params.nbThreads, cctx->customMem);
                 if (cctx->mtctx == NULL) return ERROR(memory_allocation);
             }
             DEBUGLOG(4, "call ZSTDMT_initCStream_internal as nbThreads=%u", params.nbThreads);
             CHECK_F( ZSTDMT_initCStream_internal(
-                             cctx->mtctx,
-                             prefixDict.dict, prefixDict.dictSize, ZSTD_dm_rawContent,
-                             cctx->cdict, params, cctx->pledgedSrcSizePlusOne-1) );
+                        cctx->mtctx,
+                        prefixDict.dict, prefixDict.dictSize, ZSTD_dm_rawContent,
+                        cctx->cdict, params, cctx->pledgedSrcSizePlusOne-1) );
             cctx->streamStage = zcss_load;
             cctx->appliedParams.nbThreads = params.nbThreads;
         } else
 #endif
-        {
-            CHECK_F( ZSTD_resetCStream_internal(
+        {   CHECK_F( ZSTD_resetCStream_internal(
                              cctx, prefixDict.dict, prefixDict.dictSize,
                              prefixDict.dictMode, cctx->cdict, params,
                              cctx->pledgedSrcSizePlusOne-1) );
+            assert(cctx->streamStage == zcss_load);
+            assert(cctx->appliedParams.nbThreads <= 1);
     }   }
 
     /* compression stage */
 #ifdef ZSTD_MULTITHREAD
     if (cctx->appliedParams.nbThreads > 1) {
         size_t const flushMin = ZSTDMT_compressStream_generic(cctx->mtctx, output, input, endOp);
-        DEBUGLOG(5, "ZSTDMT_compressStream_generic result : %u", (U32)flushMin);
         if ( ZSTD_isError(flushMin)
           || (endOp == ZSTD_e_end && flushMin == 0) ) { /* compression completed */
             ZSTD_startNewCompression(cctx);
@@ -2850,8 +2945,7 @@ size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output)
     {   size_t const lastBlockSize = zcs->frameEnded ? 0 : ZSTD_BLOCKHEADERSIZE;
         size_t const checksumSize = zcs->frameEnded ? 0 : zcs->appliedParams.fParams.checksumFlag * 4;
         size_t const toFlush = zcs->outBuffContentSize - zcs->outBuffFlushedSize + lastBlockSize + checksumSize;
-        DEBUGLOG(5, "ZSTD_endStream : remaining to flush : %u",
-                (unsigned)toFlush);
+        DEBUGLOG(4, "ZSTD_endStream : remaining to flush : %u", (U32)toFlush);
         return toFlush;
     }
 }
@@ -2880,12 +2974,12 @@ static const ZSTD_compressionParameters ZSTD_defaultCParameters[4][ZSTD_MAX_CLEV
     { 22, 20, 22,  5,  5, 16, ZSTD_lazy2   },  /* level 12 */
     { 22, 21, 22,  5,  5, 16, ZSTD_lazy2   },  /* level 13 */
     { 22, 21, 22,  6,  5, 16, ZSTD_lazy2   },  /* level 14 */
-    { 22, 21, 22,  5,  5, 16, ZSTD_btlazy2 },  /* level 15 */
-    { 23, 22, 22,  5,  5, 16, ZSTD_btlazy2 },  /* level 16 */
-    { 23, 22, 22,  4,  5, 24, ZSTD_btopt   },  /* level 17 */
-    { 23, 22, 22,  5,  4, 32, ZSTD_btopt   },  /* level 18 */
-    { 23, 23, 22,  6,  3, 48, ZSTD_btopt   },  /* level 19 */
-    { 25, 25, 23,  7,  3, 64, ZSTD_btultra },  /* level 20 */
+    { 22, 21, 22,  4,  5, 16, ZSTD_btlazy2 },  /* level 15 */
+    { 22, 21, 22,  4,  5, 48, ZSTD_btopt   },  /* level 16 */
+    { 23, 22, 22,  4,  4, 48, ZSTD_btopt   },  /* level 17 */
+    { 23, 22, 22,  5,  3, 64, ZSTD_btopt   },  /* level 18 */
+    { 23, 23, 22,  7,  3,128, ZSTD_btopt   },  /* level 19 */
+    { 25, 25, 23,  7,  3,128, ZSTD_btultra },  /* level 20 */
     { 26, 26, 24,  7,  3,256, ZSTD_btultra },  /* level 21 */
     { 27, 27, 25,  9,  3,512, ZSTD_btultra },  /* level 22 */
 },
@@ -3004,6 +3098,8 @@ ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long l
     }
 #endif
 
+    DEBUGLOG(4, "ZSTD_getCParams: cLevel=%i, srcSize=%u, dictSize=%u => table %u",
+                compressionLevel, (U32)srcSizeHint, (U32)dictSize, tableID);
     if (compressionLevel <= 0) compressionLevel = ZSTD_CLEVEL_DEFAULT;   /* 0 == default; no negative compressionLevel yet */
     if (compressionLevel > ZSTD_MAX_CLEVEL) compressionLevel = ZSTD_MAX_CLEVEL;
     { ZSTD_compressionParameters const cp = ZSTD_defaultCParameters[tableID][compressionLevel];
@@ -3019,5 +3115,6 @@ ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long srcSizeH
     ZSTD_compressionParameters const cParams = ZSTD_getCParams(compressionLevel, srcSizeHint, dictSize);
     memset(&params, 0, sizeof(params));
     params.cParams = cParams;
+    params.fParams.contentSizeFlag = 1;
     return params;
 }
diff --git a/thirdparty/zstd/compress/zstd_compress.h b/thirdparty/zstd/compress/zstd_compress_internal.h
index 94606edc93..f104fe981e 100644
--- a/thirdparty/zstd/compress/zstd_compress.h
+++ b/thirdparty/zstd/compress/zstd_compress_internal.h
@@ -8,6 +8,9 @@
  * You may select, at your option, one of the above-listed licenses.
  */
 
+/* This header contains definitions
+ * that shall **only** be used by modules within lib/compress.
+ */
 
 #ifndef ZSTD_COMPRESS_H
 #define ZSTD_COMPRESS_H
@@ -43,6 +46,95 @@ typedef struct ZSTD_prefixDict_s {
     ZSTD_dictMode_e dictMode;
 } ZSTD_prefixDict;
 
+typedef struct {
+    U32 hufCTable[HUF_CTABLE_SIZE_U32(255)];
+    FSE_CTable offcodeCTable[FSE_CTABLE_SIZE_U32(OffFSELog, MaxOff)];
+    FSE_CTable matchlengthCTable[FSE_CTABLE_SIZE_U32(MLFSELog, MaxML)];
+    FSE_CTable litlengthCTable[FSE_CTABLE_SIZE_U32(LLFSELog, MaxLL)];
+    U32 workspace[HUF_WORKSPACE_SIZE_U32];
+    HUF_repeat hufCTable_repeatMode;
+    FSE_repeat offcode_repeatMode;
+    FSE_repeat matchlength_repeatMode;
+    FSE_repeat litlength_repeatMode;
+} ZSTD_entropyCTables_t;
+
+typedef struct {
+    U32 off;
+    U32 len;
+} ZSTD_match_t;
+
+typedef struct {
+    int price;
+    U32 off;
+    U32 mlen;
+    U32 litlen;
+    U32 rep[ZSTD_REP_NUM];
+} ZSTD_optimal_t;
+
+typedef struct {
+    /* All tables are allocated inside cctx->workspace by ZSTD_resetCCtx_internal() */
+    U32* litFreq;               /* table of literals statistics, of size 256 */
+    U32* litLengthFreq;         /* table of litLength statistics, of size (MaxLL+1) */
+    U32* matchLengthFreq;       /* table of matchLength statistics, of size (MaxML+1) */
+    U32* offCodeFreq;           /* table of offCode statistics, of size (MaxOff+1) */
+    ZSTD_match_t* matchTable;   /* list of found matches, of size ZSTD_OPT_NUM+1 */
+    ZSTD_optimal_t* priceTable; /* All positions tracked by optimal parser, of size ZSTD_OPT_NUM+1 */
+
+    U32  litSum;                 /* nb of literals */
+    U32  litLengthSum;           /* nb of litLength codes */
+    U32  matchLengthSum;         /* nb of matchLength codes */
+    U32  offCodeSum;             /* nb of offset codes */
+    /* begin updated by ZSTD_setLog2Prices */
+    U32  log2litSum;             /* pow2 to compare log2(litfreq) to */
+    U32  log2litLengthSum;       /* pow2 to compare log2(llfreq) to */
+    U32  log2matchLengthSum;     /* pow2 to compare log2(mlfreq) to */
+    U32  log2offCodeSum;         /* pow2 to compare log2(offreq) to */
+    /* end : updated by ZSTD_setLog2Prices */
+    U32  staticPrices;           /* prices follow a pre-defined cost structure, statistics are irrelevant */
+} optState_t;
+
+typedef struct {
+    U32 offset;
+    U32 checksum;
+} ldmEntry_t;
+
+typedef struct {
+    ldmEntry_t* hashTable;
+    BYTE* bucketOffsets;    /* Next position in bucket to insert entry */
+    U64 hashPower;          /* Used to compute the rolling hash.
+                             * Depends on ldmParams.minMatchLength */
+} ldmState_t;
+
+typedef struct {
+    U32 enableLdm;          /* 1 if enable long distance matching */
+    U32 hashLog;            /* Log size of hashTable */
+    U32 bucketSizeLog;      /* Log bucket size for collision resolution, at most 8 */
+    U32 minMatchLength;     /* Minimum match length */
+    U32 hashEveryLog;       /* Log number of entries to skip */
+} ldmParams_t;
+
+struct ZSTD_CCtx_params_s {
+    ZSTD_format_e format;
+    ZSTD_compressionParameters cParams;
+    ZSTD_frameParameters fParams;
+
+    int compressionLevel;
+    U32 forceWindow;           /* force back-references to respect limit of
+                                * 1<<wLog, even for dictionary */
+
+    /* Multithreading: used to pass parameters to mtctx */
+    U32 nbThreads;
+    unsigned jobSize;
+    unsigned overlapSizeLog;
+
+    /* Long distance matching parameters */
+    ldmParams_t ldmParams;
+
+    /* For use with createCCtxParams() and freeCCtxParams() only */
+    ZSTD_customMem customMem;
+
+};  /* typedef'd to ZSTD_CCtx_params within "zstd.h" */
+
 struct ZSTD_CCtx_s {
     const BYTE* nextSrc;    /* next block here to continue on current prefix */
     const BYTE* base;       /* All regular indexes relative to this position */
@@ -99,38 +191,51 @@ struct ZSTD_CCtx_s {
 };
 
 
-static const BYTE LL_Code[64] = {  0,  1,  2,  3,  4,  5,  6,  7,
-                                   8,  9, 10, 11, 12, 13, 14, 15,
-                                  16, 16, 17, 17, 18, 18, 19, 19,
-                                  20, 20, 20, 20, 21, 21, 21, 21,
-                                  22, 22, 22, 22, 22, 22, 22, 22,
-                                  23, 23, 23, 23, 23, 23, 23, 23,
-                                  24, 24, 24, 24, 24, 24, 24, 24,
-                                  24, 24, 24, 24, 24, 24, 24, 24 };
-
-static const BYTE ML_Code[128] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
-                                  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
-                                  32, 32, 33, 33, 34, 34, 35, 35, 36, 36, 36, 36, 37, 37, 37, 37,
-                                  38, 38, 38, 38, 38, 38, 38, 38, 39, 39, 39, 39, 39, 39, 39, 39,
-                                  40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
-                                  41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
-                                  42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
-                                  42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42 };
+MEM_STATIC U32 ZSTD_LLcode(U32 litLength)
+{
+    static const BYTE LL_Code[64] = {  0,  1,  2,  3,  4,  5,  6,  7,
+                                       8,  9, 10, 11, 12, 13, 14, 15,
+                                      16, 16, 17, 17, 18, 18, 19, 19,
+                                      20, 20, 20, 20, 21, 21, 21, 21,
+                                      22, 22, 22, 22, 22, 22, 22, 22,
+                                      23, 23, 23, 23, 23, 23, 23, 23,
+                                      24, 24, 24, 24, 24, 24, 24, 24,
+                                      24, 24, 24, 24, 24, 24, 24, 24 };
+    static const U32 LL_deltaCode = 19;
+    return (litLength > 63) ? ZSTD_highbit32(litLength) + LL_deltaCode : LL_Code[litLength];
+}
+
+/* ZSTD_MLcode() :
+ * note : mlBase = matchLength - MINMATCH;
+ *        because it's the format it's stored in seqStore->sequences */
+MEM_STATIC U32 ZSTD_MLcode(U32 mlBase)
+{
+    static const BYTE ML_Code[128] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
+                                      16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
+                                      32, 32, 33, 33, 34, 34, 35, 35, 36, 36, 36, 36, 37, 37, 37, 37,
+                                      38, 38, 38, 38, 38, 38, 38, 38, 39, 39, 39, 39, 39, 39, 39, 39,
+                                      40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
+                                      41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
+                                      42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+                                      42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42 };
+    static const U32 ML_deltaCode = 36;
+    return (mlBase > 127) ? ZSTD_highbit32(mlBase) + ML_deltaCode : ML_Code[mlBase];
+}
 
 /*! ZSTD_storeSeq() :
-    Store a sequence (literal length, literals, offset code and match length code) into seqStore_t.
-    `offsetCode` : distance to match, or 0 == repCode.
-    `matchCode` : matchLength - MINMATCH
+ *  Store a sequence (literal length, literals, offset code and match length code) into seqStore_t.
+ *  `offsetCode` : distance to match + 3 (values 1-3 are repCodes).
+ *  `mlBase` : matchLength - MINMATCH
 */
-MEM_STATIC void ZSTD_storeSeq(seqStore_t* seqStorePtr, size_t litLength, const void* literals, U32 offsetCode, size_t matchCode)
+MEM_STATIC void ZSTD_storeSeq(seqStore_t* seqStorePtr, size_t litLength, const void* literals, U32 offsetCode, size_t mlBase)
 {
 #if defined(ZSTD_DEBUG) && (ZSTD_DEBUG >= 6)
     static const BYTE* g_start = NULL;
-    U32 const pos = (U32)((const BYTE*)literals - g_start);
-    if (g_start==NULL) g_start = (const BYTE*)literals;
-    if ((pos > 0) && (pos < 1000000000))
-        DEBUGLOG(6, "Cpos %6u :%5u literals & match %3u bytes at distance %6u",
-               pos, (U32)litLength, (U32)matchCode+MINMATCH, (U32)offsetCode);
+    if (g_start==NULL) g_start = (const BYTE*)literals;  /* note : index only works for compression within a single segment */
+    {   U32 const pos = (U32)((const BYTE*)literals - g_start);
+        DEBUGLOG(6, "Cpos%7u :%3u literals, match%3u bytes at dist.code%7u",
+               pos, (U32)litLength, (U32)mlBase+MINMATCH, (U32)offsetCode);
+    }
 #endif
     /* copy Literals */
     assert(seqStorePtr->lit + litLength <= seqStorePtr->litStart + 128 KB);
@@ -139,6 +244,7 @@ MEM_STATIC void ZSTD_storeSeq(seqStore_t* seqStorePtr, size_t litLength, const v
 
     /* literal Length */
     if (litLength>0xFFFF) {
+        assert(seqStorePtr->longLengthID == 0); /* there can only be a single long length */
         seqStorePtr->longLengthID = 1;
         seqStorePtr->longLengthPos = (U32)(seqStorePtr->sequences - seqStorePtr->sequencesStart);
     }
@@ -148,11 +254,12 @@ MEM_STATIC void ZSTD_storeSeq(seqStore_t* seqStorePtr, size_t litLength, const v
     seqStorePtr->sequences[0].offset = offsetCode + 1;
 
     /* match Length */
-    if (matchCode>0xFFFF) {
+    if (mlBase>0xFFFF) {
+        assert(seqStorePtr->longLengthID == 0); /* there can only be a single long length */
         seqStorePtr->longLengthID = 2;
         seqStorePtr->longLengthPos = (U32)(seqStorePtr->sequences - seqStorePtr->sequencesStart);
     }
-    seqStorePtr->sequences[0].matchLength = (U16)matchCode;
+    seqStorePtr->sequences[0].matchLength = (U16)mlBase;
 
     seqStorePtr->sequences++;
 }
@@ -161,7 +268,7 @@ MEM_STATIC void ZSTD_storeSeq(seqStore_t* seqStorePtr, size_t litLength, const v
 /*-*************************************
 *  Match length counter
 ***************************************/
-static unsigned ZSTD_NbCommonBytes (register size_t val)
+static unsigned ZSTD_NbCommonBytes (size_t val)
 {
     if (MEM_isLittleEndian()) {
         if (MEM_64bits()) {
@@ -235,13 +342,17 @@ MEM_STATIC size_t ZSTD_count(const BYTE* pIn, const BYTE* pMatch, const BYTE* co
     const BYTE* const pStart = pIn;
     const BYTE* const pInLoopLimit = pInLimit - (sizeof(size_t)-1);
 
-    while (pIn < pInLoopLimit) {
-        size_t const diff = MEM_readST(pMatch) ^ MEM_readST(pIn);
-        if (!diff) { pIn+=sizeof(size_t); pMatch+=sizeof(size_t); continue; }
-        pIn += ZSTD_NbCommonBytes(diff);
-        return (size_t)(pIn - pStart);
-    }
-    if (MEM_64bits()) if ((pIn<(pInLimit-3)) && (MEM_read32(pMatch) == MEM_read32(pIn))) { pIn+=4; pMatch+=4; }
+    if (pIn < pInLoopLimit) {
+        { size_t const diff = MEM_readST(pMatch) ^ MEM_readST(pIn);
+          if (diff) return ZSTD_NbCommonBytes(diff); }
+        pIn+=sizeof(size_t); pMatch+=sizeof(size_t);
+        while (pIn < pInLoopLimit) {
+            size_t const diff = MEM_readST(pMatch) ^ MEM_readST(pIn);
+            if (!diff) { pIn+=sizeof(size_t); pMatch+=sizeof(size_t); continue; }
+            pIn += ZSTD_NbCommonBytes(diff);
+            return (size_t)(pIn - pStart);
+    }   }
+    if (MEM_64bits() && (pIn<(pInLimit-3)) && (MEM_read32(pMatch) == MEM_read32(pIn))) { pIn+=4; pMatch+=4; }
     if ((pIn<(pInLimit-1)) && (MEM_read16(pMatch) == MEM_read16(pIn))) { pIn+=2; pMatch+=2; }
     if ((pIn<pInLimit) && (*pMatch == *pIn)) pIn++;
     return (size_t)(pIn - pStart);
@@ -304,4 +415,48 @@ MEM_STATIC size_t ZSTD_hashPtr(const void* p, U32 hBits, U32 mls)
 }
 #endif
 
+
+/* ==============================================================
+ * Private declarations
+ * These prototypes shall only be called from within lib/compress
+ * ============================================================== */
+
+/*! ZSTD_initCStream_internal() :
+ *  Private use only. Init streaming operation.
+ *  expects params to be valid.
+ *  must receive dict, or cdict, or none, but not both.
+ *  @return : 0, or an error code */
+size_t ZSTD_initCStream_internal(ZSTD_CStream* zcs,
+                     const void* dict, size_t dictSize,
+                     const ZSTD_CDict* cdict,
+                     ZSTD_CCtx_params  params, unsigned long long pledgedSrcSize);
+
+/*! ZSTD_compressStream_generic() :
+ *  Private use only. To be called from zstdmt_compress.c in single-thread mode. */
+size_t ZSTD_compressStream_generic(ZSTD_CStream* zcs,
+                                   ZSTD_outBuffer* output,
+                                   ZSTD_inBuffer* input,
+                                   ZSTD_EndDirective const flushMode);
+
+/*! ZSTD_getCParamsFromCDict() :
+ *  as the name implies */
+ZSTD_compressionParameters ZSTD_getCParamsFromCDict(const ZSTD_CDict* cdict);
+
+/* ZSTD_compressBegin_advanced_internal() :
+ * Private use only. To be called from zstdmt_compress.c. */
+size_t ZSTD_compressBegin_advanced_internal(ZSTD_CCtx* cctx,
+                                    const void* dict, size_t dictSize,
+                                    ZSTD_dictMode_e dictMode,
+                                    const ZSTD_CDict* cdict,
+                                    ZSTD_CCtx_params params,
+                                    unsigned long long pledgedSrcSize);
+
+/* ZSTD_compress_advanced_internal() :
+ * Private use only. To be called from zstdmt_compress.c. */
+size_t ZSTD_compress_advanced_internal(ZSTD_CCtx* cctx,
+                                       void* dst, size_t dstCapacity,
+                                 const void* src, size_t srcSize,
+                                 const void* dict,size_t dictSize,
+                                 ZSTD_CCtx_params params);
+
 #endif /* ZSTD_COMPRESS_H */
diff --git a/thirdparty/zstd/compress/zstd_double_fast.c b/thirdparty/zstd/compress/zstd_double_fast.c
index 876a36042c..fee5127c35 100644
--- a/thirdparty/zstd/compress/zstd_double_fast.c
+++ b/thirdparty/zstd/compress/zstd_double_fast.c
@@ -8,6 +8,7 @@
  * You may select, at your option, one of the above-listed licenses.
  */
 
+#include "zstd_compress_internal.h"
 #include "zstd_double_fast.h"
 
 
diff --git a/thirdparty/zstd/compress/zstd_double_fast.h b/thirdparty/zstd/compress/zstd_double_fast.h
index 3dba6c7108..75e0415809 100644
--- a/thirdparty/zstd/compress/zstd_double_fast.h
+++ b/thirdparty/zstd/compress/zstd_double_fast.h
@@ -11,12 +11,13 @@
 #ifndef ZSTD_DOUBLE_FAST_H
 #define ZSTD_DOUBLE_FAST_H
 
-#include "zstd_compress.h"
-
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
+#include "mem.h"      /* U32 */
+#include "zstd.h"     /* ZSTD_CCtx, size_t */
+
 void ZSTD_fillDoubleHashTable(ZSTD_CCtx* cctx, const void* end, const U32 mls);
 size_t ZSTD_compressBlock_doubleFast(ZSTD_CCtx* ctx, const void* src, size_t srcSize);
 size_t ZSTD_compressBlock_doubleFast_extDict(ZSTD_CCtx* ctx, const void* src, size_t srcSize);
diff --git a/thirdparty/zstd/compress/zstd_fast.c b/thirdparty/zstd/compress/zstd_fast.c
index 2e057017b9..7b56c3d6ad 100644
--- a/thirdparty/zstd/compress/zstd_fast.c
+++ b/thirdparty/zstd/compress/zstd_fast.c
@@ -8,6 +8,7 @@
  * You may select, at your option, one of the above-listed licenses.
  */
 
+#include "zstd_compress_internal.h"
 #include "zstd_fast.h"
 
 
diff --git a/thirdparty/zstd/compress/zstd_fast.h b/thirdparty/zstd/compress/zstd_fast.h
index 4205141a9a..d8b7771954 100644
--- a/thirdparty/zstd/compress/zstd_fast.h
+++ b/thirdparty/zstd/compress/zstd_fast.h
@@ -11,12 +11,13 @@
 #ifndef ZSTD_FAST_H
 #define ZSTD_FAST_H
 
-#include "zstd_compress.h"
-
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
+#include "mem.h"      /* U32 */
+#include "zstd.h"     /* ZSTD_CCtx, size_t */
+
 void ZSTD_fillHashTable(ZSTD_CCtx* zc, const void* end, const U32 mls);
 size_t ZSTD_compressBlock_fast(ZSTD_CCtx* ctx,
                          const void* src, size_t srcSize);
diff --git a/thirdparty/zstd/compress/zstd_lazy.c b/thirdparty/zstd/compress/zstd_lazy.c
index 2a7f6a0fe2..6d4804961d 100644
--- a/thirdparty/zstd/compress/zstd_lazy.c
+++ b/thirdparty/zstd/compress/zstd_lazy.c
@@ -8,6 +8,7 @@
  * You may select, at your option, one of the above-listed licenses.
  */
 
+#include "zstd_compress_internal.h"
 #include "zstd_lazy.h"
 
 
@@ -15,10 +16,11 @@
 *  Binary Tree search
 ***************************************/
 /** ZSTD_insertBt1() : add one or multiple positions to tree.
-*   ip : assumed <= iend-8 .
-*   @return : nb of positions added */
-static U32 ZSTD_insertBt1(ZSTD_CCtx* zc, const BYTE* const ip, const U32 mls, const BYTE* const iend, U32 nbCompares,
-                          U32 extDict)
+ *  ip : assumed <= iend-8 .
+ * @return : nb of positions added */
+static U32 ZSTD_insertBt1(ZSTD_CCtx* zc,
+                const BYTE* const ip, const BYTE* const iend,
+                U32 nbCompares, U32 const mls, U32 const extDict)
 {
     U32*   const hashTable = zc->hashTable;
     U32    const hashLog = zc->appliedParams.cParams.hashLog;
@@ -40,7 +42,7 @@ static U32 ZSTD_insertBt1(ZSTD_CCtx* zc, const BYTE* const ip, const U32 mls, co
     U32* largerPtr  = smallerPtr + 1;
     U32 dummy32;   /* to be nullified at the end */
     U32 const windowLow = zc->lowLimit;
-    U32 matchEndIdx = current+8;
+    U32 matchEndIdx = current+8+1;
     size_t bestLength = 8;
 #ifdef ZSTD_C_PREDICT
     U32 predictedSmall = *(bt + 2*((current-1)&btMask) + 0);
@@ -49,12 +51,15 @@ static U32 ZSTD_insertBt1(ZSTD_CCtx* zc, const BYTE* const ip, const U32 mls, co
     predictedLarge += (predictedLarge>0);
 #endif /* ZSTD_C_PREDICT */
 
+    DEBUGLOG(8, "ZSTD_insertBt1 (%u)", current);
+
     assert(ip <= iend-8);   /* required for h calculation */
     hashTable[h] = current;   /* Update Hash Table */
 
     while (nbCompares-- && (matchIndex > windowLow)) {
         U32* const nextPtr = bt + 2*(matchIndex & btMask);
         size_t matchLength = MIN(commonLengthSmaller, commonLengthLarger);   /* guaranteed minimum nb of common bytes */
+        assert(matchIndex < current);
 
 #ifdef ZSTD_C_PREDICT   /* note : can create issues when hlog small <= 11 */
         const U32* predictPtr = bt + 2*((matchIndex-1) & btMask);   /* written this way, as bt is a roll buffer */
@@ -76,10 +81,11 @@ static U32 ZSTD_insertBt1(ZSTD_CCtx* zc, const BYTE* const ip, const U32 mls, co
             continue;
         }
 #endif
+
         if ((!extDict) || (matchIndex+matchLength >= dictLimit)) {
+            assert(matchIndex+matchLength >= dictLimit);   /* might be wrong if extDict is incorrectly set to 0 */
             match = base + matchIndex;
-            if (match[matchLength] == ip[matchLength])
-                matchLength += ZSTD_count(ip+matchLength+1, match+matchLength+1, iend) +1;
+            matchLength += ZSTD_count(ip+matchLength, match+matchLength, iend);
         } else {
             match = dictBase + matchIndex;
             matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iend, dictEnd, prefixStart);
@@ -93,16 +99,17 @@ static U32 ZSTD_insertBt1(ZSTD_CCtx* zc, const BYTE* const ip, const U32 mls, co
                 matchEndIdx = matchIndex + (U32)matchLength;
         }
 
-        if (ip+matchLength == iend)   /* equal : no way to know if inf or sup */
+        if (ip+matchLength == iend) {   /* equal : no way to know if inf or sup */
             break;   /* drop , to guarantee consistency ; miss a bit of compression, but other solutions can corrupt tree */
+        }
 
         if (match[matchLength] < ip[matchLength]) {  /* necessarily within buffer */
-            /* match+1 is smaller than current */
+            /* match is smaller than current */
             *smallerPtr = matchIndex;             /* update smaller idx */
             commonLengthSmaller = matchLength;    /* all smaller will now have at least this guaranteed common length */
             if (matchIndex <= btLow) { smallerPtr=&dummy32; break; }   /* beyond tree size, stop searching */
-            smallerPtr = nextPtr+1;               /* new "smaller" => larger of match */
-            matchIndex = nextPtr[1];              /* new matchIndex larger than previous (closer to current) */
+            smallerPtr = nextPtr+1;               /* new "candidate" => larger than match, which was smaller than target */
+            matchIndex = nextPtr[1];              /* new matchIndex, larger than previous and closer to current */
         } else {
             /* match is larger than current */
             *largerPtr = matchIndex;
@@ -114,8 +121,38 @@ static U32 ZSTD_insertBt1(ZSTD_CCtx* zc, const BYTE* const ip, const U32 mls, co
 
     *smallerPtr = *largerPtr = 0;
     if (bestLength > 384) return MIN(192, (U32)(bestLength - 384));   /* speed optimization */
-    if (matchEndIdx > current + 8) return matchEndIdx - (current + 8);
-    return 1;
+    assert(matchEndIdx > current + 8);
+    return matchEndIdx - (current + 8);
+}
+
+FORCE_INLINE_TEMPLATE
+void ZSTD_updateTree_internal(ZSTD_CCtx* zc,
+                const BYTE* const ip, const BYTE* const iend,
+                const U32 nbCompares, const U32 mls, const U32 extDict)
+{
+    const BYTE* const base = zc->base;
+    U32 const target = (U32)(ip - base);
+    U32 idx = zc->nextToUpdate;
+    DEBUGLOG(7, "ZSTD_updateTree_internal, from %u to %u  (extDict:%u)",
+                idx, target, extDict);
+
+    while(idx < target)
+        idx += ZSTD_insertBt1(zc, base+idx, iend, nbCompares, mls, extDict);
+    zc->nextToUpdate = target;
+}
+
+void ZSTD_updateTree(ZSTD_CCtx* zc,
+                const BYTE* const ip, const BYTE* const iend,
+                const U32 nbCompares, const U32 mls)
+{
+    ZSTD_updateTree_internal(zc, ip, iend, nbCompares, mls, 0 /*extDict*/);
+}
+
+void ZSTD_updateTree_extDict(ZSTD_CCtx* zc,
+                const BYTE* const ip, const BYTE* const iend,
+                const U32 nbCompares, const U32 mls)
+{
+    ZSTD_updateTree_internal(zc, ip, iend, nbCompares, mls, 1 /*extDict*/);
 }
 
 
@@ -144,7 +181,7 @@ static size_t ZSTD_insertBtAndFindBestMatch (
     const U32 windowLow = zc->lowLimit;
     U32* smallerPtr = bt + 2*(current&btMask);
     U32* largerPtr  = bt + 2*(current&btMask) + 1;
-    U32 matchEndIdx = current+8;
+    U32 matchEndIdx = current+8+1;
     U32 dummy32;   /* to be nullified at the end */
     size_t bestLength = 0;
 
@@ -158,8 +195,7 @@ static size_t ZSTD_insertBtAndFindBestMatch (
 
         if ((!extDict) || (matchIndex+matchLength >= dictLimit)) {
             match = base + matchIndex;
-            if (match[matchLength] == ip[matchLength])
-                matchLength += ZSTD_count(ip+matchLength+1, match+matchLength+1, iend) +1;
+            matchLength += ZSTD_count(ip+matchLength, match+matchLength, iend);
         } else {
             match = dictBase + matchIndex;
             matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iend, dictEnd, prefixStart);
@@ -172,8 +208,9 @@ static size_t ZSTD_insertBtAndFindBestMatch (
                 matchEndIdx = matchIndex + (U32)matchLength;
             if ( (4*(int)(matchLength-bestLength)) > (int)(ZSTD_highbit32(current-matchIndex+1) - ZSTD_highbit32((U32)offsetPtr[0]+1)) )
                 bestLength = matchLength, *offsetPtr = ZSTD_REP_MOVE + current - matchIndex;
-            if (ip+matchLength == iend)   /* equal : no way to know if inf or sup */
+            if (ip+matchLength == iend) {   /* equal : no way to know if inf or sup */
                 break;   /* drop, to guarantee consistency (miss a little bit of compression) */
+            }
         }
 
         if (match[matchLength] < ip[matchLength]) {
@@ -194,21 +231,12 @@ static size_t ZSTD_insertBtAndFindBestMatch (
 
     *smallerPtr = *largerPtr = 0;
 
-    zc->nextToUpdate = (matchEndIdx > current + 8) ? matchEndIdx - 8 : current+1;
+    assert(matchEndIdx > current+8);
+    zc->nextToUpdate = matchEndIdx - 8;   /* skip repetitive patterns */
     return bestLength;
 }
 
 
-void ZSTD_updateTree(ZSTD_CCtx* zc, const BYTE* const ip, const BYTE* const iend, const U32 nbCompares, const U32 mls)
-{
-    const BYTE* const base = zc->base;
-    const U32 target = (U32)(ip - base);
-    U32 idx = zc->nextToUpdate;
-
-    while(idx < target)
-        idx += ZSTD_insertBt1(zc, base+idx, mls, iend, nbCompares, 0);
-}
-
 /** ZSTD_BtFindBestMatch() : Tree updater, providing best match */
 static size_t ZSTD_BtFindBestMatch (
                         ZSTD_CCtx* zc,
@@ -239,16 +267,6 @@ static size_t ZSTD_BtFindBestMatch_selectMLS (
 }
 
 
-void ZSTD_updateTree_extDict(ZSTD_CCtx* zc, const BYTE* const ip, const BYTE* const iend, const U32 nbCompares, const U32 mls)
-{
-    const BYTE* const base = zc->base;
-    const U32 target = (U32)(ip - base);
-    U32 idx = zc->nextToUpdate;
-
-    while (idx < target) idx += ZSTD_insertBt1(zc, base+idx, mls, iend, nbCompares, 1);
-}
-
-
 /** Tree updater, providing best match */
 static size_t ZSTD_BtFindBestMatch_extDict (
                         ZSTD_CCtx* zc,
@@ -335,14 +353,14 @@ size_t ZSTD_HcFindBestMatch_generic (
     U32 matchIndex = ZSTD_insertAndFindFirstIndex (zc, ip, mls);
 
     for ( ; (matchIndex>lowLimit) & (nbAttempts>0) ; nbAttempts--) {
-        const BYTE* match;
         size_t currentMl=0;
         if ((!extDict) || matchIndex >= dictLimit) {
-            match = base + matchIndex;
+            const BYTE* const match = base + matchIndex;
             if (match[ml] == ip[ml])   /* potentially better */
                 currentMl = ZSTD_count(ip, match, iLimit);
         } else {
-            match = dictBase + matchIndex;
+            const BYTE* const match = dictBase + matchIndex;
+            assert(match+4 <= dictEnd);
             if (MEM_read32(match) == MEM_read32(ip))   /* assumption : matchIndex <= dictLimit-4 (by table construction) */
                 currentMl = ZSTD_count_2segments(ip+4, match+4, iLimit, dictEnd, prefixStart) + 4;
         }
@@ -380,10 +398,10 @@ FORCE_INLINE_TEMPLATE size_t ZSTD_HcFindBestMatch_selectMLS (
 
 
 FORCE_INLINE_TEMPLATE size_t ZSTD_HcFindBestMatch_extDict_selectMLS (
-                        ZSTD_CCtx* zc,
+                        ZSTD_CCtx* const zc,
                         const BYTE* ip, const BYTE* const iLimit,
-                        size_t* offsetPtr,
-                        const U32 maxNbAttempts, const U32 matchLengthSearch)
+                        size_t* const offsetPtr,
+                        U32 const maxNbAttempts, U32 const matchLengthSearch)
 {
     switch(matchLengthSearch)
     {
@@ -502,9 +520,8 @@ size_t ZSTD_compressBlock_lazy_generic(ZSTD_CCtx* ctx,
          */
         /* catch up */
         if (offset) {
-            while ( (start > anchor)
-                 && (start > base+offset-ZSTD_REP_MOVE)
-                 && (start[-1] == (start-offset+ZSTD_REP_MOVE)[-1]) )  /* only search for offset within prefix */
+            while ( ((start > anchor) & (start - (offset-ZSTD_REP_MOVE) > base))
+                 && (start[-1] == (start-(offset-ZSTD_REP_MOVE))[-1]) )  /* only search for offset within prefix */
                 { start--; matchLength++; }
             offset_2 = offset_1; offset_1 = (U32)(offset - ZSTD_REP_MOVE);
         }
@@ -516,9 +533,8 @@ _storeSequence:
         }
 
         /* check immediate repcode */
-        while ( (ip <= ilimit)
-             && ((offset_2>0)
-             & (MEM_read32(ip) == MEM_read32(ip - offset_2)) )) {
+        while ( ((ip <= ilimit) & (offset_2>0))
+             && (MEM_read32(ip) == MEM_read32(ip - offset_2)) ) {
             /* store sequence */
             matchLength = ZSTD_count(ip+4, ip+4-offset_2, iend) + 4;
             offset = offset_2; offset_2 = offset_1; offset_1 = (U32)offset; /* swap repcodes */
diff --git a/thirdparty/zstd/compress/zstd_lazy.h b/thirdparty/zstd/compress/zstd_lazy.h
index a9c4daed25..74e1fd6970 100644
--- a/thirdparty/zstd/compress/zstd_lazy.h
+++ b/thirdparty/zstd/compress/zstd_lazy.h
@@ -11,12 +11,13 @@
 #ifndef ZSTD_LAZY_H
 #define ZSTD_LAZY_H
 
-#include "zstd_compress.h"
-
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
+#include "mem.h"    /* U32 */
+#include "zstd.h"   /* ZSTD_CCtx, size_t */
+
 U32 ZSTD_insertAndFindFirstIndex (ZSTD_CCtx* zc, const BYTE* ip, U32 mls);
 void ZSTD_updateTree(ZSTD_CCtx* zc, const BYTE* const ip, const BYTE* const iend, const U32 nbCompares, const U32 mls);
 void ZSTD_updateTree_extDict(ZSTD_CCtx* zc, const BYTE* const ip, const BYTE* const iend, const U32 nbCompares, const U32 mls);
diff --git a/thirdparty/zstd/compress/zstd_ldm.h b/thirdparty/zstd/compress/zstd_ldm.h
index d6d3d42c33..8f12c677aa 100644
--- a/thirdparty/zstd/compress/zstd_ldm.h
+++ b/thirdparty/zstd/compress/zstd_ldm.h
@@ -10,12 +10,13 @@
 #ifndef ZSTD_LDM_H
 #define ZSTD_LDM_H
 
-#include "zstd_compress.h"
-
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
+#include "zstd_compress_internal.h"   /* ldmParams_t, U32 */
+#include "zstd.h"   /* ZSTD_CCtx, size_t */
+
 /*-*************************************
 *  Long distance matching
 ***************************************/
diff --git a/thirdparty/zstd/compress/zstd_opt.c b/thirdparty/zstd/compress/zstd_opt.c
index c47ce23ad5..7171ff5373 100644
--- a/thirdparty/zstd/compress/zstd_opt.c
+++ b/thirdparty/zstd/compress/zstd_opt.c
@@ -8,36 +8,35 @@
  * You may select, at your option, one of the above-listed licenses.
  */
 
+#include "zstd_compress_internal.h"
 #include "zstd_opt.h"
-#include "zstd_lazy.h"
+#include "zstd_lazy.h"   /* ZSTD_updateTree, ZSTD_updateTree_extDict */
 
 
-#define ZSTD_LITFREQ_ADD    2
-#define ZSTD_FREQ_DIV       4
-#define ZSTD_MAX_PRICE      (1<<30)
+#define ZSTD_LITFREQ_ADD    2   /* scaling factor for litFreq, so that frequencies adapt faster to new stats. Also used for matchSum (?) */
+#define ZSTD_FREQ_DIV       4   /* log factor when using previous stats to init next stats */
+#define ZSTD_MAX_PRICE     (1<<30)
+
 
 /*-*************************************
 *  Price functions for optimal parser
 ***************************************/
 static void ZSTD_setLog2Prices(optState_t* optPtr)
 {
-    optPtr->log2matchLengthSum = ZSTD_highbit32(optPtr->matchLengthSum+1);
-    optPtr->log2litLengthSum = ZSTD_highbit32(optPtr->litLengthSum+1);
     optPtr->log2litSum = ZSTD_highbit32(optPtr->litSum+1);
+    optPtr->log2litLengthSum = ZSTD_highbit32(optPtr->litLengthSum+1);
+    optPtr->log2matchLengthSum = ZSTD_highbit32(optPtr->matchLengthSum+1);
     optPtr->log2offCodeSum = ZSTD_highbit32(optPtr->offCodeSum+1);
-    optPtr->factor = 1 + ((optPtr->litSum>>5) / optPtr->litLengthSum) + ((optPtr->litSum<<1) / (optPtr->litSum + optPtr->matchSum));
 }
 
 
-static void ZSTD_rescaleFreqs(optState_t* optPtr, const BYTE* src, size_t srcSize)
+static void ZSTD_rescaleFreqs(optState_t* const optPtr,
+                              const BYTE* const src, size_t const srcSize)
 {
-    unsigned u;
-
-    optPtr->cachedLiterals = NULL;
-    optPtr->cachedPrice = optPtr->cachedLitLength = 0;
     optPtr->staticPrices = 0;
 
-    if (optPtr->litLengthSum == 0) {
+    if (optPtr->litLengthSum == 0) {  /* first init */
+        unsigned u;
         if (srcSize <= 1024) optPtr->staticPrices = 1;
 
         assert(optPtr->litFreq!=NULL);
@@ -45,44 +44,41 @@ static void ZSTD_rescaleFreqs(optState_t* optPtr, const BYTE* src, size_t srcSiz
             optPtr->litFreq[u] = 0;
         for (u=0; u<srcSize; u++)
             optPtr->litFreq[src[u]]++;
-
         optPtr->litSum = 0;
-        optPtr->litLengthSum = MaxLL+1;
-        optPtr->matchLengthSum = MaxML+1;
-        optPtr->offCodeSum = (MaxOff+1);
-        optPtr->matchSum = (ZSTD_LITFREQ_ADD<<Litbits);
-
         for (u=0; u<=MaxLit; u++) {
-            optPtr->litFreq[u] = 1 + (optPtr->litFreq[u]>>ZSTD_FREQ_DIV);
+            optPtr->litFreq[u] = 1 + (optPtr->litFreq[u] >> ZSTD_FREQ_DIV);
             optPtr->litSum += optPtr->litFreq[u];
         }
+
         for (u=0; u<=MaxLL; u++)
             optPtr->litLengthFreq[u] = 1;
+        optPtr->litLengthSum = MaxLL+1;
         for (u=0; u<=MaxML; u++)
             optPtr->matchLengthFreq[u] = 1;
+        optPtr->matchLengthSum = MaxML+1;
         for (u=0; u<=MaxOff; u++)
             optPtr->offCodeFreq[u] = 1;
+        optPtr->offCodeSum = (MaxOff+1);
+
     } else {
-        optPtr->matchLengthSum = 0;
-        optPtr->litLengthSum = 0;
-        optPtr->offCodeSum = 0;
-        optPtr->matchSum = 0;
-        optPtr->litSum = 0;
+        unsigned u;
 
+        optPtr->litSum = 0;
         for (u=0; u<=MaxLit; u++) {
-            optPtr->litFreq[u] = 1 + (optPtr->litFreq[u]>>(ZSTD_FREQ_DIV+1));
+            optPtr->litFreq[u] = 1 + (optPtr->litFreq[u] >> (ZSTD_FREQ_DIV+1));
             optPtr->litSum += optPtr->litFreq[u];
         }
+        optPtr->litLengthSum = 0;
         for (u=0; u<=MaxLL; u++) {
             optPtr->litLengthFreq[u] = 1 + (optPtr->litLengthFreq[u]>>(ZSTD_FREQ_DIV+1));
             optPtr->litLengthSum += optPtr->litLengthFreq[u];
         }
+        optPtr->matchLengthSum = 0;
         for (u=0; u<=MaxML; u++) {
             optPtr->matchLengthFreq[u] = 1 + (optPtr->matchLengthFreq[u]>>ZSTD_FREQ_DIV);
             optPtr->matchLengthSum += optPtr->matchLengthFreq[u];
-            optPtr->matchSum += optPtr->matchLengthFreq[u] * (u + 3);
         }
-        optPtr->matchSum *= ZSTD_LITFREQ_ADD;
+        optPtr->offCodeSum = 0;
         for (u=0; u<=MaxOff; u++) {
             optPtr->offCodeFreq[u] = 1 + (optPtr->offCodeFreq[u]>>ZSTD_FREQ_DIV);
             optPtr->offCodeSum += optPtr->offCodeFreq[u];
@@ -93,114 +89,146 @@ static void ZSTD_rescaleFreqs(optState_t* optPtr, const BYTE* src, size_t srcSiz
 }
 
 
-static U32 ZSTD_getLiteralPrice(optState_t* optPtr, U32 litLength, const BYTE* literals)
+/* ZSTD_rawLiteralsCost() :
+ * cost of literals (only) in given segment (which length can be null)
+ * does not include cost of literalLength symbol */
+static U32 ZSTD_rawLiteralsCost(const BYTE* const literals, U32 const litLength,
+                                const optState_t* const optPtr)
 {
-    U32 price, u;
-
-    if (optPtr->staticPrices)
-        return ZSTD_highbit32((U32)litLength+1) + (litLength*6);
-
-    if (litLength == 0)
-        return optPtr->log2litLengthSum - ZSTD_highbit32(optPtr->litLengthFreq[0]+1);
+    if (optPtr->staticPrices) return (litLength*6);  /* 6 bit per literal - no statistic used */
+    if (litLength == 0) return 0;
 
     /* literals */
-    if (optPtr->cachedLiterals == literals) {
-        U32 const additional = litLength - optPtr->cachedLitLength;
-        const BYTE* literals2 = optPtr->cachedLiterals + optPtr->cachedLitLength;
-        price = optPtr->cachedPrice + additional * optPtr->log2litSum;
-        for (u=0; u < additional; u++)
-            price -= ZSTD_highbit32(optPtr->litFreq[literals2[u]]+1);
-        optPtr->cachedPrice = price;
-        optPtr->cachedLitLength = litLength;
-    } else {
-        price = litLength * optPtr->log2litSum;
+    {   U32 u;
+        U32 cost = litLength * optPtr->log2litSum;
         for (u=0; u < litLength; u++)
-            price -= ZSTD_highbit32(optPtr->litFreq[literals[u]]+1);
-
-        if (litLength >= 12) {
-            optPtr->cachedLiterals = literals;
-            optPtr->cachedPrice = price;
-            optPtr->cachedLitLength = litLength;
-        }
+            cost -= ZSTD_highbit32(optPtr->litFreq[literals[u]]+1);
+        return cost;
     }
+}
+
+/* ZSTD_litLengthPrice() :
+ * cost of literalLength symbol */
+static U32 ZSTD_litLengthPrice(U32 const litLength, const optState_t* const optPtr)
+{
+    if (optPtr->staticPrices) return ZSTD_highbit32((U32)litLength+1);
 
     /* literal Length */
-    {   const BYTE LL_deltaCode = 19;
-        const BYTE llCode = (litLength>63) ? (BYTE)ZSTD_highbit32(litLength) + LL_deltaCode : LL_Code[litLength];
-        price += LL_bits[llCode] + optPtr->log2litLengthSum - ZSTD_highbit32(optPtr->litLengthFreq[llCode]+1);
+    {   U32 const llCode = ZSTD_LLcode(litLength);
+        U32 const price = LL_bits[llCode] + optPtr->log2litLengthSum - ZSTD_highbit32(optPtr->litLengthFreq[llCode]+1);
+        return price;
     }
+}
 
-    return price;
+/* ZSTD_litLengthPrice() :
+ * cost of the literal part of a sequence,
+ * including literals themselves, and literalLength symbol */
+static U32 ZSTD_fullLiteralsCost(const BYTE* const literals, U32 const litLength,
+                                 const optState_t* const optPtr)
+{
+    return ZSTD_rawLiteralsCost(literals, litLength, optPtr)
+         + ZSTD_litLengthPrice(litLength, optPtr);
+}
+
+/* ZSTD_litLengthContribution() :
+ * @return ( cost(litlength) - cost(0) )
+ * this value can then be added to rawLiteralsCost()
+ * to provide a cost which is directly comparable to a match ending at same position */
+static int ZSTD_litLengthContribution(U32 const litLength, const optState_t* const optPtr)
+{
+    if (optPtr->staticPrices) return ZSTD_highbit32(litLength+1);
+
+    /* literal Length */
+    {   U32 const llCode = ZSTD_LLcode(litLength);
+        int const contribution = LL_bits[llCode]
+                        + ZSTD_highbit32(optPtr->litLengthFreq[0]+1)
+                        - ZSTD_highbit32(optPtr->litLengthFreq[llCode]+1);
+#if 1
+        return contribution;
+#else
+        return MAX(0, contribution); /* sometimes better, sometimes not ... */
+#endif
+    }
 }
 
+/* ZSTD_literalsContribution() :
+ * creates a fake cost for the literals part of a sequence
+ * which can be compared to the ending cost of a match
+ * should a new match start at this position */
+static int ZSTD_literalsContribution(const BYTE* const literals, U32 const litLength,
+                                     const optState_t* const optPtr)
+{
+    int const contribution = ZSTD_rawLiteralsCost(literals, litLength, optPtr)
+                           + ZSTD_litLengthContribution(litLength, optPtr);
+    return contribution;
+}
 
-FORCE_INLINE_TEMPLATE U32 ZSTD_getPrice(optState_t* optPtr, U32 litLength, const BYTE* literals, U32 offset, U32 matchLength, const int ultra)
+/* ZSTD_getMatchPrice() :
+ * Provides the cost of the match part (offset + matchLength) of a sequence
+ * Must be combined with ZSTD_fullLiteralsCost() to get the full cost of a sequence.
+ * optLevel: when <2, favors small offset for decompression speed (improved cache efficiency) */
+FORCE_INLINE_TEMPLATE U32 ZSTD_getMatchPrice(
+                                    U32 const offset, U32 const matchLength,
+                                    const optState_t* const optPtr,
+                                    int const optLevel)
 {
-    /* offset */
     U32 price;
-    BYTE const offCode = (BYTE)ZSTD_highbit32(offset+1);
+    U32 const offCode = ZSTD_highbit32(offset+1);
+    U32 const mlBase = matchLength - MINMATCH;
+    assert(matchLength >= MINMATCH);
 
-    if (optPtr->staticPrices)
-        return ZSTD_getLiteralPrice(optPtr, litLength, literals) + ZSTD_highbit32((U32)matchLength+1) + 16 + offCode;
+    if (optPtr->staticPrices)  /* fixed scheme, do not use statistics */
+        return ZSTD_highbit32((U32)mlBase+1) + 16 + offCode;
 
     price = offCode + optPtr->log2offCodeSum - ZSTD_highbit32(optPtr->offCodeFreq[offCode]+1);
-    if (!ultra && offCode >= 20) price += (offCode-19)*2;
+    if ((optLevel<2) /*static*/ && offCode >= 20) price += (offCode-19)*2; /* handicap for long distance offsets, favor decompression speed */
 
     /* match Length */
-    {   const BYTE ML_deltaCode = 36;
-        const BYTE mlCode = (matchLength>127) ? (BYTE)ZSTD_highbit32(matchLength) + ML_deltaCode : ML_Code[matchLength];
+    {   U32 const mlCode = ZSTD_MLcode(mlBase);
         price += ML_bits[mlCode] + optPtr->log2matchLengthSum - ZSTD_highbit32(optPtr->matchLengthFreq[mlCode]+1);
     }
 
-    return price + ZSTD_getLiteralPrice(optPtr, litLength, literals) + optPtr->factor;
+    DEBUGLOG(8, "ZSTD_getMatchPrice(ml:%u) = %u", matchLength, price);
+    return price;
 }
 
-
-static void ZSTD_updatePrice(optState_t* optPtr, U32 litLength, const BYTE* literals, U32 offset, U32 matchLength)
+static void ZSTD_updateStats(optState_t* const optPtr,
+                             U32 litLength, const BYTE* literals,
+                             U32 offsetCode, U32 matchLength)
 {
-    U32 u;
-
     /* literals */
-    optPtr->litSum += litLength*ZSTD_LITFREQ_ADD;
-    for (u=0; u < litLength; u++)
-        optPtr->litFreq[literals[u]] += ZSTD_LITFREQ_ADD;
+    {   U32 u;
+        for (u=0; u < litLength; u++)
+            optPtr->litFreq[literals[u]] += ZSTD_LITFREQ_ADD;
+        optPtr->litSum += litLength*ZSTD_LITFREQ_ADD;
+    }
 
     /* literal Length */
-    {   const BYTE LL_deltaCode = 19;
-        const BYTE llCode = (litLength>63) ? (BYTE)ZSTD_highbit32(litLength) + LL_deltaCode : LL_Code[litLength];
+    {   U32 const llCode = ZSTD_LLcode(litLength);
         optPtr->litLengthFreq[llCode]++;
         optPtr->litLengthSum++;
     }
 
-    /* match offset */
-    {   BYTE const offCode = (BYTE)ZSTD_highbit32(offset+1);
-        optPtr->offCodeSum++;
+    /* match offset code (0-2=>repCode; 3+=>offset+2) */
+    {   U32 const offCode = ZSTD_highbit32(offsetCode+1);
+        assert(offCode <= MaxOff);
         optPtr->offCodeFreq[offCode]++;
+        optPtr->offCodeSum++;
     }
 
     /* match Length */
-    {   const BYTE ML_deltaCode = 36;
-        const BYTE mlCode = (matchLength>127) ? (BYTE)ZSTD_highbit32(matchLength) + ML_deltaCode : ML_Code[matchLength];
+    {   U32 const mlBase = matchLength - MINMATCH;
+        U32 const mlCode = ZSTD_MLcode(mlBase);
         optPtr->matchLengthFreq[mlCode]++;
         optPtr->matchLengthSum++;
     }
-
-    ZSTD_setLog2Prices(optPtr);
 }
 
 
-#define SET_PRICE(pos, mlen_, offset_, litlen_, price_)   \
-    {                                                 \
-        while (last_pos < pos)  { opt[last_pos+1].price = ZSTD_MAX_PRICE; last_pos++; } \
-        opt[pos].mlen = mlen_;                         \
-        opt[pos].off = offset_;                        \
-        opt[pos].litlen = litlen_;                     \
-        opt[pos].price = price_;                       \
-    }
-
-
-/* function safe only for comparisons */
-static U32 ZSTD_readMINMATCH(const void* memPtr, U32 length)
+/* ZSTD_readMINMATCH() :
+ * function safe only for comparisons
+ * assumption : memPtr must be at least 4 bytes before end of buffer */
+MEM_STATIC U32 ZSTD_readMINMATCH(const void* memPtr, U32 length)
 {
     switch (length)
     {
@@ -216,15 +244,14 @@ static U32 ZSTD_readMINMATCH(const void* memPtr, U32 length)
 
 /* Update hashTable3 up to ip (excluded)
    Assumption : always within prefix (i.e. not within extDict) */
-static
-U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_CCtx* zc, const BYTE* ip)
+static U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_CCtx* const cctx, const BYTE* const ip)
 {
-    U32* const hashTable3  = zc->hashTable3;
-    U32 const hashLog3  = zc->hashLog3;
-    const BYTE* const base = zc->base;
-    U32 idx = zc->nextToUpdate3;
-    const U32 target = zc->nextToUpdate3 = (U32)(ip - base);
-    const size_t hash3 = ZSTD_hash3Ptr(ip, hashLog3);
+    U32* const hashTable3  = cctx->hashTable3;
+    U32 const hashLog3  = cctx->hashLog3;
+    const BYTE* const base = cctx->base;
+    U32 idx = cctx->nextToUpdate3;
+    U32 const target = cctx->nextToUpdate3 = (U32)(ip - base);
+    size_t const hash3 = ZSTD_hash3Ptr(ip, hashLog3);
 
     while(idx < target) {
         hashTable3[ZSTD_hash3Ptr(base+idx, hashLog3)] = idx;
@@ -238,102 +265,147 @@ U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_CCtx* zc, const BYTE* ip)
 /*-*************************************
 *  Binary Tree search
 ***************************************/
-static U32 ZSTD_insertBtAndGetAllMatches (
-                        ZSTD_CCtx* zc,
-                        const BYTE* const ip, const BYTE* const iLimit,
-                        U32 nbCompares, const U32 mls,
-                        U32 extDict, ZSTD_match_t* matches, const U32 minMatchLen)
+FORCE_INLINE_TEMPLATE
+U32 ZSTD_insertBtAndGetAllMatches (
+                    ZSTD_CCtx* zc,
+                    const BYTE* const ip, const BYTE* const iLimit, int const extDict,
+                    U32 nbCompares, U32 const mls, U32 const sufficient_len,
+                    U32 rep[ZSTD_REP_NUM], U32 const ll0,
+                    ZSTD_match_t* matches, const U32 lengthToBeat)
 {
     const BYTE* const base = zc->base;
-    const U32 current = (U32)(ip-base);
-    const U32 hashLog = zc->appliedParams.cParams.hashLog;
-    const size_t h  = ZSTD_hashPtr(ip, hashLog, mls);
+    U32 const current = (U32)(ip-base);
+    U32 const hashLog = zc->appliedParams.cParams.hashLog;
+    U32 const minMatch = (mls==3) ? 3 : 4;
     U32* const hashTable = zc->hashTable;
+    size_t const h  = ZSTD_hashPtr(ip, hashLog, mls);
     U32 matchIndex  = hashTable[h];
     U32* const bt   = zc->chainTable;
-    const U32 btLog = zc->appliedParams.cParams.chainLog - 1;
-    const U32 btMask= (1U << btLog) - 1;
+    U32 const btLog = zc->appliedParams.cParams.chainLog - 1;
+    U32 const btMask= (1U << btLog) - 1;
     size_t commonLengthSmaller=0, commonLengthLarger=0;
     const BYTE* const dictBase = zc->dictBase;
-    const U32 dictLimit = zc->dictLimit;
+    U32 const dictLimit = zc->dictLimit;
     const BYTE* const dictEnd = dictBase + dictLimit;
     const BYTE* const prefixStart = base + dictLimit;
-    const U32 btLow = btMask >= current ? 0 : current - btMask;
-    const U32 windowLow = zc->lowLimit;
+    U32 const btLow = btMask >= current ? 0 : current - btMask;
+    U32 const windowLow = zc->lowLimit;
     U32* smallerPtr = bt + 2*(current&btMask);
     U32* largerPtr  = bt + 2*(current&btMask) + 1;
-    U32 matchEndIdx = current+8;
+    U32 matchEndIdx = current+8+1;   /* farthest referenced position of any match => detects repetitive patterns */
     U32 dummy32;   /* to be nullified at the end */
     U32 mnum = 0;
 
-    const U32 minMatch = (mls == 3) ? 3 : 4;
-    size_t bestLength = minMatchLen-1;
+    size_t bestLength = lengthToBeat-1;
+    DEBUGLOG(7, "ZSTD_insertBtAndGetAllMatches");
+
+    /* check repCode */
+    {   U32 const lastR = ZSTD_REP_NUM + ll0;
+        U32 repCode;
+        for (repCode = ll0; repCode < lastR; repCode++) {
+            U32 const repOffset = (repCode==ZSTD_REP_NUM) ? (rep[0] - 1) : rep[repCode];
+            U32 const repIndex = current - repOffset;
+            U32 repLen = 0;
+            assert(current >= dictLimit);
+            if (repOffset-1 /* intentional overflow, discards 0 and -1 */ < current-dictLimit) {  /* equivalent to `current > repIndex >= dictLimit` */
+                if (ZSTD_readMINMATCH(ip, minMatch) == ZSTD_readMINMATCH(ip - repOffset, minMatch)) {
+                    repLen = (U32)ZSTD_count(ip+minMatch, ip+minMatch-repOffset, iLimit) + minMatch;
+                }
+            } else {  /* repIndex < dictLimit || repIndex >= current */
+                const BYTE* const repMatch = dictBase + repIndex;
+                assert(current >= windowLow);
+                if ( extDict /* this case only valid in extDict mode */
+                  && ( ((repOffset-1) /*intentional overflow*/ < current - windowLow)  /* equivalent to `current > repIndex >= windowLow` */
+                     & (((U32)((dictLimit-1) - repIndex) >= 3) ) /* intentional overflow : do not test positions overlapping 2 memory segments */)
+                  && (ZSTD_readMINMATCH(ip, minMatch) == ZSTD_readMINMATCH(repMatch, minMatch)) ) {
+                    repLen = (U32)ZSTD_count_2segments(ip+minMatch, repMatch+minMatch, iLimit, dictEnd, prefixStart) + minMatch;
+            }   }
+            /* save longer solution */
+            if (repLen > bestLength) {
+                DEBUGLOG(8, "found rep-match %u of length %u",
+                            repCode - ll0, (U32)repLen);
+                bestLength = repLen;
+                matches[mnum].off = repCode - ll0;
+                matches[mnum].len = (U32)repLen;
+                mnum++;
+                if ( (repLen > sufficient_len)
+                   | (ip+repLen == iLimit) ) {  /* best possible */
+                    return mnum;
+    }   }   }   }
 
-    if (minMatch == 3) { /* HC3 match finder */
+    /* HC3 match finder */
+    if ((mls == 3) /*static*/ && (bestLength < mls)) {
         U32 const matchIndex3 = ZSTD_insertAndFindFirstIndexHash3 (zc, ip);
-        if (matchIndex3>windowLow && (current - matchIndex3 < (1<<18))) {
-            const BYTE* match;
-            size_t currentMl=0;
-            if ((!extDict) || matchIndex3 >= dictLimit) {
-                match = base + matchIndex3;
-                if (match[bestLength] == ip[bestLength]) currentMl = ZSTD_count(ip, match, iLimit);
+        if ((matchIndex3 > windowLow)
+          & (current - matchIndex3 < (1<<18)) /*heuristic : longer distance likely too expensive*/ ) {
+            size_t mlen;
+            if ((!extDict) /*static*/ || (matchIndex3 >= dictLimit)) {
+                const BYTE* const match = base + matchIndex3;
+                mlen = ZSTD_count(ip, match, iLimit);
             } else {
-                match = dictBase + matchIndex3;
-                if (ZSTD_readMINMATCH(match, MINMATCH) == ZSTD_readMINMATCH(ip, MINMATCH))    /* assumption : matchIndex3 <= dictLimit-4 (by table construction) */
-                    currentMl = ZSTD_count_2segments(ip+MINMATCH, match+MINMATCH, iLimit, dictEnd, prefixStart) + MINMATCH;
+                const BYTE* const match = dictBase + matchIndex3;
+                mlen = ZSTD_count_2segments(ip, match, iLimit, dictEnd, prefixStart);
             }
 
             /* save best solution */
-            if (currentMl > bestLength) {
-                bestLength = currentMl;
-                matches[mnum].off = ZSTD_REP_MOVE_OPT + current - matchIndex3;
-                matches[mnum].len = (U32)currentMl;
-                mnum++;
-                if (currentMl > ZSTD_OPT_NUM) goto update;
-                if (ip+currentMl == iLimit) goto update; /* best possible, and avoid read overflow*/
-            }
-        }
-    }
+            if (mlen >= mls /* == 3 > bestLength */) {
+                DEBUGLOG(8, "found small match with hlog3, of length %u",
+                            (U32)mlen);
+                bestLength = mlen;
+                assert(current > matchIndex3);
+                assert(mnum==0);  /* no prior solution */
+                matches[0].off = (current - matchIndex3) + ZSTD_REP_MOVE;
+                matches[0].len = (U32)mlen;
+                mnum = 1;
+                if ( (mlen > sufficient_len) |
+                     (ip+mlen == iLimit) ) {  /* best possible length */
+                    zc->nextToUpdate = current+1;  /* skip insertion */
+                    return 1;
+    }   }   }   }
 
     hashTable[h] = current;   /* Update Hash Table */
 
     while (nbCompares-- && (matchIndex > windowLow)) {
-        U32* nextPtr = bt + 2*(matchIndex & btMask);
+        U32* const nextPtr = bt + 2*(matchIndex & btMask);
         size_t matchLength = MIN(commonLengthSmaller, commonLengthLarger);   /* guaranteed minimum nb of common bytes */
         const BYTE* match;
+        assert(current > matchIndex);
 
         if ((!extDict) || (matchIndex+matchLength >= dictLimit)) {
+            assert(matchIndex+matchLength >= dictLimit);  /* ensure the condition is correct when !extDict */
             match = base + matchIndex;
-            if (match[matchLength] == ip[matchLength]) {
-                matchLength += ZSTD_count(ip+matchLength+1, match+matchLength+1, iLimit) +1;
-            }
+            matchLength += ZSTD_count(ip+matchLength, match+matchLength, iLimit);
         } else {
             match = dictBase + matchIndex;
             matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iLimit, dictEnd, prefixStart);
             if (matchIndex+matchLength >= dictLimit)
-                match = base + matchIndex;   /* to prepare for next usage of match[matchLength] */
+                match = base + matchIndex;   /* prepare for match[matchLength] */
         }
 
         if (matchLength > bestLength) {
-            if (matchLength > matchEndIdx - matchIndex) matchEndIdx = matchIndex + (U32)matchLength;
+            DEBUGLOG(8, "found match of length %u at distance %u",
+                    (U32)matchLength, current - matchIndex);
+            assert(matchEndIdx > matchIndex);
+            if (matchLength > matchEndIdx - matchIndex)
+                matchEndIdx = matchIndex + (U32)matchLength;
             bestLength = matchLength;
-            matches[mnum].off = ZSTD_REP_MOVE_OPT + current - matchIndex;
+            matches[mnum].off = (current - matchIndex) + ZSTD_REP_MOVE;
             matches[mnum].len = (U32)matchLength;
             mnum++;
             if (matchLength > ZSTD_OPT_NUM) break;
-            if (ip+matchLength == iLimit)   /* equal : no way to know if inf or sup */
-                break;   /* drop, to guarantee consistency (miss a little bit of compression) */
+            if (ip+matchLength == iLimit) {  /* equal : no way to know if inf or sup */
+                break;   /* drop, to preserve bt consistency (miss a little bit of compression) */
+            }
         }
 
         if (match[matchLength] < ip[matchLength]) {
-            /* match is smaller than current */
+            /* match smaller than current */
             *smallerPtr = matchIndex;             /* update smaller idx */
             commonLengthSmaller = matchLength;    /* all smaller will now have at least this guaranteed common length */
             if (matchIndex <= btLow) { smallerPtr=&dummy32; break; }   /* beyond tree size, stop the search */
-            smallerPtr = nextPtr+1;               /* new "smaller" => larger of match */
-            matchIndex = nextPtr[1];              /* new matchIndex larger than previous (closer to current) */
+            smallerPtr = nextPtr+1;               /* new candidate => larger than match, which was smaller than current */
+            matchIndex = nextPtr[1];              /* new matchIndex, larger than previous, closer to current */
         } else {
-            /* match is larger than current */
             *largerPtr = matchIndex;
             commonLengthLarger = matchLength;
             if (matchIndex <= btLow) { largerPtr=&dummy32; break; }   /* beyond tree size, stop the search */
@@ -343,65 +415,31 @@ static U32 ZSTD_insertBtAndGetAllMatches (
 
     *smallerPtr = *largerPtr = 0;
 
-update:
-    zc->nextToUpdate = (matchEndIdx > current + 8) ? matchEndIdx - 8 : current+1;
+    assert(matchEndIdx > current+8);
+    zc->nextToUpdate = matchEndIdx - 8;  /* skip repetitive patterns */
     return mnum;
 }
 
 
-/** Tree updater, providing best match */
-static U32 ZSTD_BtGetAllMatches (
-                        ZSTD_CCtx* zc,
-                        const BYTE* const ip, const BYTE* const iLimit,
-                        const U32 maxNbAttempts, const U32 mls, ZSTD_match_t* matches, const U32 minMatchLen)
-{
-    if (ip < zc->base + zc->nextToUpdate) return 0;   /* skipped area */
-    ZSTD_updateTree(zc, ip, iLimit, maxNbAttempts, mls);
-    return ZSTD_insertBtAndGetAllMatches(zc, ip, iLimit, maxNbAttempts, mls, 0, matches, minMatchLen);
-}
-
-
-static U32 ZSTD_BtGetAllMatches_selectMLS (
+FORCE_INLINE_TEMPLATE U32 ZSTD_BtGetAllMatches (
                         ZSTD_CCtx* zc,   /* Index table will be updated */
-                        const BYTE* ip, const BYTE* const iHighLimit,
-                        const U32 maxNbAttempts, const U32 matchLengthSearch, ZSTD_match_t* matches, const U32 minMatchLen)
-{
-    switch(matchLengthSearch)
-    {
-    case 3 : return ZSTD_BtGetAllMatches(zc, ip, iHighLimit, maxNbAttempts, 3, matches, minMatchLen);
-    default :
-    case 4 : return ZSTD_BtGetAllMatches(zc, ip, iHighLimit, maxNbAttempts, 4, matches, minMatchLen);
-    case 5 : return ZSTD_BtGetAllMatches(zc, ip, iHighLimit, maxNbAttempts, 5, matches, minMatchLen);
-    case 7 :
-    case 6 : return ZSTD_BtGetAllMatches(zc, ip, iHighLimit, maxNbAttempts, 6, matches, minMatchLen);
-    }
-}
-
-/** Tree updater, providing best match */
-static U32 ZSTD_BtGetAllMatches_extDict (
-                        ZSTD_CCtx* zc,
-                        const BYTE* const ip, const BYTE* const iLimit,
-                        const U32 maxNbAttempts, const U32 mls, ZSTD_match_t* matches, const U32 minMatchLen)
+                        const BYTE* ip, const BYTE* const iHighLimit, int const extDict,
+                        U32 const maxNbAttempts, U32 const matchLengthSearch, U32 const sufficient_len,
+                        U32 rep[ZSTD_REP_NUM], U32 const ll0,
+                        ZSTD_match_t* matches, U32 const lengthToBeat)
 {
+    DEBUGLOG(7, "ZSTD_BtGetAllMatches");
     if (ip < zc->base + zc->nextToUpdate) return 0;   /* skipped area */
-    ZSTD_updateTree_extDict(zc, ip, iLimit, maxNbAttempts, mls);
-    return ZSTD_insertBtAndGetAllMatches(zc, ip, iLimit, maxNbAttempts, mls, 1, matches, minMatchLen);
-}
-
-
-static U32 ZSTD_BtGetAllMatches_selectMLS_extDict (
-                        ZSTD_CCtx* zc,   /* Index table will be updated */
-                        const BYTE* ip, const BYTE* const iHighLimit,
-                        const U32 maxNbAttempts, const U32 matchLengthSearch, ZSTD_match_t* matches, const U32 minMatchLen)
-{
+    if (extDict) ZSTD_updateTree_extDict(zc, ip, iHighLimit, maxNbAttempts, matchLengthSearch);
+    else ZSTD_updateTree(zc, ip, iHighLimit, maxNbAttempts, matchLengthSearch);
     switch(matchLengthSearch)
     {
-    case 3 : return ZSTD_BtGetAllMatches_extDict(zc, ip, iHighLimit, maxNbAttempts, 3, matches, minMatchLen);
+    case 3 : return ZSTD_insertBtAndGetAllMatches(zc, ip, iHighLimit, extDict, maxNbAttempts, 3, sufficient_len, rep, ll0, matches, lengthToBeat);
     default :
-    case 4 : return ZSTD_BtGetAllMatches_extDict(zc, ip, iHighLimit, maxNbAttempts, 4, matches, minMatchLen);
-    case 5 : return ZSTD_BtGetAllMatches_extDict(zc, ip, iHighLimit, maxNbAttempts, 5, matches, minMatchLen);
+    case 4 : return ZSTD_insertBtAndGetAllMatches(zc, ip, iHighLimit, extDict, maxNbAttempts, 4, sufficient_len, rep, ll0, matches, lengthToBeat);
+    case 5 : return ZSTD_insertBtAndGetAllMatches(zc, ip, iHighLimit, extDict, maxNbAttempts, 5, sufficient_len, rep, ll0, matches, lengthToBeat);
     case 7 :
-    case 6 : return ZSTD_BtGetAllMatches_extDict(zc, ip, iHighLimit, maxNbAttempts, 6, matches, minMatchLen);
+    case 6 : return ZSTD_insertBtAndGetAllMatches(zc, ip, iHighLimit, extDict, maxNbAttempts, 6, sufficient_len, rep, ll0, matches, lengthToBeat);
     }
 }
 
@@ -409,534 +447,313 @@ static U32 ZSTD_BtGetAllMatches_selectMLS_extDict (
 /*-*******************************
 *  Optimal parser
 *********************************/
-FORCE_INLINE_TEMPLATE
-size_t ZSTD_compressBlock_opt_generic(ZSTD_CCtx* ctx,
-                                      const void* src, size_t srcSize, const int ultra)
-{
-    seqStore_t* seqStorePtr = &(ctx->seqStore);
-    optState_t* optStatePtr = &(ctx->optState);
-    const BYTE* const istart = (const BYTE*)src;
-    const BYTE* ip = istart;
-    const BYTE* anchor = istart;
-    const BYTE* const iend = istart + srcSize;
-    const BYTE* const ilimit = iend - 8;
-    const BYTE* const base = ctx->base;
-    const BYTE* const prefixStart = base + ctx->dictLimit;
-
-    const U32 maxSearches = 1U << ctx->appliedParams.cParams.searchLog;
-    const U32 sufficient_len = ctx->appliedParams.cParams.targetLength;
-    const U32 mls = ctx->appliedParams.cParams.searchLength;
-    const U32 minMatch = (ctx->appliedParams.cParams.searchLength == 3) ? 3 : 4;
-
-    ZSTD_optimal_t* opt = optStatePtr->priceTable;
-    ZSTD_match_t* matches = optStatePtr->matchTable;
-    const BYTE* inr;
-    U32 offset, rep[ZSTD_REP_NUM];
-
-    /* init */
-    ctx->nextToUpdate3 = ctx->nextToUpdate;
-    ZSTD_rescaleFreqs(optStatePtr, (const BYTE*)src, srcSize);
-    ip += (ip==prefixStart);
-    { U32 i; for (i=0; i<ZSTD_REP_NUM; i++) rep[i]=seqStorePtr->rep[i]; }
-
-    /* Match Loop */
-    while (ip < ilimit) {
-        U32 cur, match_num, last_pos, litlen, price;
-        U32 u, mlen, best_mlen, best_off, litLength;
-        memset(opt, 0, sizeof(ZSTD_optimal_t));
-        last_pos = 0;
-        litlen = (U32)(ip - anchor);
-
-        /* check repCode */
-        {   U32 i, last_i = ZSTD_REP_CHECK + (ip==anchor);
-            for (i=(ip == anchor); i<last_i; i++) {
-                const S32 repCur = (i==ZSTD_REP_MOVE_OPT) ? (rep[0] - 1) : rep[i];
-                if ( (repCur > 0) && (repCur < (S32)(ip-prefixStart))
-                    && (ZSTD_readMINMATCH(ip, minMatch) == ZSTD_readMINMATCH(ip - repCur, minMatch))) {
-                    mlen = (U32)ZSTD_count(ip+minMatch, ip+minMatch-repCur, iend) + minMatch;
-                    if (mlen > sufficient_len || mlen >= ZSTD_OPT_NUM) {
-                        best_mlen = mlen; best_off = i; cur = 0; last_pos = 1;
-                        goto _storeSequence;
-                    }
-                    best_off = i - (ip == anchor);
-                    do {
-                        price = ZSTD_getPrice(optStatePtr, litlen, anchor, best_off, mlen - MINMATCH, ultra);
-                        if (mlen > last_pos || price < opt[mlen].price)
-                            SET_PRICE(mlen, mlen, i, litlen, price);   /* note : macro modifies last_pos */
-                        mlen--;
-                    } while (mlen >= minMatch);
-        }   }   }
-
-        match_num = ZSTD_BtGetAllMatches_selectMLS(ctx, ip, iend, maxSearches, mls, matches, minMatch);
-
-        if (!last_pos && !match_num) { ip++; continue; }
-
-        if (match_num && (matches[match_num-1].len > sufficient_len || matches[match_num-1].len >= ZSTD_OPT_NUM)) {
-            best_mlen = matches[match_num-1].len;
-            best_off = matches[match_num-1].off;
-            cur = 0;
-            last_pos = 1;
-            goto _storeSequence;
-        }
-
-        /* set prices using matches at position = 0 */
-        best_mlen = (last_pos) ? last_pos : minMatch;
-        for (u = 0; u < match_num; u++) {
-            mlen = (u>0) ? matches[u-1].len+1 : best_mlen;
-            best_mlen = matches[u].len;
-            while (mlen <= best_mlen) {
-                price = ZSTD_getPrice(optStatePtr, litlen, anchor, matches[u].off-1, mlen - MINMATCH, ultra);
-                if (mlen > last_pos || price < opt[mlen].price)
-                    SET_PRICE(mlen, mlen, matches[u].off, litlen, price);   /* note : macro modifies last_pos */
-                mlen++;
-        }   }
-
-        if (last_pos < minMatch) { ip++; continue; }
-
-        /* initialize opt[0] */
-        { U32 i ; for (i=0; i<ZSTD_REP_NUM; i++) opt[0].rep[i] = rep[i]; }
-        opt[0].mlen = 1;
-        opt[0].litlen = litlen;
-
-         /* check further positions */
-        for (cur = 1; cur <= last_pos; cur++) {
-           inr = ip + cur;
-
-           if (opt[cur-1].mlen == 1) {
-                litlen = opt[cur-1].litlen + 1;
-                if (cur > litlen) {
-                    price = opt[cur - litlen].price + ZSTD_getLiteralPrice(optStatePtr, litlen, inr-litlen);
-                } else
-                    price = ZSTD_getLiteralPrice(optStatePtr, litlen, anchor);
-           } else {
-                litlen = 1;
-                price = opt[cur - 1].price + ZSTD_getLiteralPrice(optStatePtr, litlen, inr-1);
-           }
-
-           if (cur > last_pos || price <= opt[cur].price)
-                SET_PRICE(cur, 1, 0, litlen, price);
-
-           if (cur == last_pos) break;
-
-           if (inr > ilimit)  /* last match must start at a minimum distance of 8 from oend */
-               continue;
-
-           mlen = opt[cur].mlen;
-           if (opt[cur].off > ZSTD_REP_MOVE_OPT) {
-                opt[cur].rep[2] = opt[cur-mlen].rep[1];
-                opt[cur].rep[1] = opt[cur-mlen].rep[0];
-                opt[cur].rep[0] = opt[cur].off - ZSTD_REP_MOVE_OPT;
-           } else {
-                opt[cur].rep[2] = (opt[cur].off > 1) ? opt[cur-mlen].rep[1] : opt[cur-mlen].rep[2];
-                opt[cur].rep[1] = (opt[cur].off > 0) ? opt[cur-mlen].rep[0] : opt[cur-mlen].rep[1];
-                /* If opt[cur].off == ZSTD_REP_MOVE_OPT, then mlen != 1.
-                 * offset ZSTD_REP_MOVE_OPT is used for the special case
-                 * litLength == 0, where offset 0 means something special.
-                 * mlen == 1 means the previous byte was stored as a literal,
-                 * so they are mutually exclusive.
-                 */
-                assert(!(opt[cur].off == ZSTD_REP_MOVE_OPT && mlen == 1));
-                opt[cur].rep[0] = (opt[cur].off == ZSTD_REP_MOVE_OPT) ? (opt[cur-mlen].rep[0] - 1) : (opt[cur-mlen].rep[opt[cur].off]);
-           }
-
-            best_mlen = minMatch;
-            {   U32 i, last_i = ZSTD_REP_CHECK + (mlen != 1);
-                for (i=(opt[cur].mlen != 1); i<last_i; i++) {  /* check rep */
-                    const S32 repCur = (i==ZSTD_REP_MOVE_OPT) ? (opt[cur].rep[0] - 1) : opt[cur].rep[i];
-                    if ( (repCur > 0) && (repCur < (S32)(inr-prefixStart))
-                       && (ZSTD_readMINMATCH(inr, minMatch) == ZSTD_readMINMATCH(inr - repCur, minMatch))) {
-                       mlen = (U32)ZSTD_count(inr+minMatch, inr+minMatch - repCur, iend) + minMatch;
-
-                       if (mlen > sufficient_len || cur + mlen >= ZSTD_OPT_NUM) {
-                            best_mlen = mlen; best_off = i; last_pos = cur + 1;
-                            goto _storeSequence;
-                       }
-
-                       best_off = i - (opt[cur].mlen != 1);
-                       if (mlen > best_mlen) best_mlen = mlen;
-
-                       do {
-                           if (opt[cur].mlen == 1) {
-                                litlen = opt[cur].litlen;
-                                if (cur > litlen) {
-                                    price = opt[cur - litlen].price + ZSTD_getPrice(optStatePtr, litlen, inr-litlen, best_off, mlen - MINMATCH, ultra);
-                                } else
-                                    price = ZSTD_getPrice(optStatePtr, litlen, anchor, best_off, mlen - MINMATCH, ultra);
-                            } else {
-                                litlen = 0;
-                                price = opt[cur].price + ZSTD_getPrice(optStatePtr, 0, NULL, best_off, mlen - MINMATCH, ultra);
-                            }
-
-                            if (cur + mlen > last_pos || price <= opt[cur + mlen].price)
-                                SET_PRICE(cur + mlen, mlen, i, litlen, price);
-                            mlen--;
-                        } while (mlen >= minMatch);
-            }   }   }
-
-            match_num = ZSTD_BtGetAllMatches_selectMLS(ctx, inr, iend, maxSearches, mls, matches, best_mlen);
-
-            if (match_num > 0 && (matches[match_num-1].len > sufficient_len || cur + matches[match_num-1].len >= ZSTD_OPT_NUM)) {
-                best_mlen = matches[match_num-1].len;
-                best_off = matches[match_num-1].off;
-                last_pos = cur + 1;
-                goto _storeSequence;
-            }
-
-            /* set prices using matches at position = cur */
-            for (u = 0; u < match_num; u++) {
-                mlen = (u>0) ? matches[u-1].len+1 : best_mlen;
-                best_mlen = matches[u].len;
-
-                while (mlen <= best_mlen) {
-                    if (opt[cur].mlen == 1) {
-                        litlen = opt[cur].litlen;
-                        if (cur > litlen)
-                            price = opt[cur - litlen].price + ZSTD_getPrice(optStatePtr, litlen, ip+cur-litlen, matches[u].off-1, mlen - MINMATCH, ultra);
-                        else
-                            price = ZSTD_getPrice(optStatePtr, litlen, anchor, matches[u].off-1, mlen - MINMATCH, ultra);
-                    } else {
-                        litlen = 0;
-                        price = opt[cur].price + ZSTD_getPrice(optStatePtr, 0, NULL, matches[u].off-1, mlen - MINMATCH, ultra);
-                    }
-
-                    if (cur + mlen > last_pos || (price < opt[cur + mlen].price))
-                        SET_PRICE(cur + mlen, mlen, matches[u].off, litlen, price);
+typedef struct repcodes_s {
+    U32 rep[3];
+} repcodes_t;
 
-                    mlen++;
-        }   }   }
-
-        best_mlen = opt[last_pos].mlen;
-        best_off = opt[last_pos].off;
-        cur = last_pos - best_mlen;
-
-        /* store sequence */
-_storeSequence:   /* cur, last_pos, best_mlen, best_off have to be set */
-        opt[0].mlen = 1;
-
-        while (1) {
-            mlen = opt[cur].mlen;
-            offset = opt[cur].off;
-            opt[cur].mlen = best_mlen;
-            opt[cur].off = best_off;
-            best_mlen = mlen;
-            best_off = offset;
-            if (mlen > cur) break;
-            cur -= mlen;
-        }
-
-        for (u = 0; u <= last_pos;) {
-            u += opt[u].mlen;
+repcodes_t ZSTD_updateRep(U32 const rep[3], U32 const offset, U32 const ll0)
+{
+    repcodes_t newReps;
+    if (offset >= ZSTD_REP_NUM) {  /* full offset */
+        newReps.rep[2] = rep[1];
+        newReps.rep[1] = rep[0];
+        newReps.rep[0] = offset - ZSTD_REP_MOVE;
+    } else {   /* repcode */
+        U32 const repCode = offset + ll0;
+        if (repCode > 0) {  /* note : if repCode==0, no change */
+            U32 const currentOffset = (repCode==ZSTD_REP_NUM) ? (rep[0] - 1) : rep[repCode];
+            newReps.rep[2] = (repCode >= 2) ? rep[1] : rep[2];
+            newReps.rep[1] = rep[0];
+            newReps.rep[0] = currentOffset;
+        } else {   /* repCode == 0 */
+            memcpy(&newReps, rep, sizeof(newReps));
         }
+    }
+    return newReps;
+}
 
-        for (cur=0; cur < last_pos; ) {
-            mlen = opt[cur].mlen;
-            if (mlen == 1) { ip++; cur++; continue; }
-            offset = opt[cur].off;
-            cur += mlen;
-            litLength = (U32)(ip - anchor);
-
-            if (offset > ZSTD_REP_MOVE_OPT) {
-                rep[2] = rep[1];
-                rep[1] = rep[0];
-                rep[0] = offset - ZSTD_REP_MOVE_OPT;
-                offset--;
-            } else {
-                if (offset != 0) {
-                    best_off = (offset==ZSTD_REP_MOVE_OPT) ? (rep[0] - 1) : (rep[offset]);
-                    if (offset != 1) rep[2] = rep[1];
-                    rep[1] = rep[0];
-                    rep[0] = best_off;
-                }
-                if (litLength==0) offset--;
-            }
 
-            ZSTD_updatePrice(optStatePtr, litLength, anchor, offset, mlen-MINMATCH);
-            ZSTD_storeSeq(seqStorePtr, litLength, anchor, offset, mlen-MINMATCH);
-            anchor = ip = ip + mlen;
-    }    }   /* for (cur=0; cur < last_pos; ) */
+typedef struct {
+    const BYTE* anchor;
+    U32 litlen;
+    U32 rawLitCost;
+} cachedLiteralPrice_t;
 
-    /* Save reps for next block */
-    { int i; for (i=0; i<ZSTD_REP_NUM; i++) seqStorePtr->repToConfirm[i] = rep[i]; }
+static U32 ZSTD_rawLiteralsCost_cached(
+                            cachedLiteralPrice_t* const cachedLitPrice,
+                            const BYTE* const anchor, U32 const litlen,
+                            const optState_t* const optStatePtr)
+{
+    U32 startCost;
+    U32 remainingLength;
+    const BYTE* startPosition;
+
+    if (anchor == cachedLitPrice->anchor) {
+        startCost = cachedLitPrice->rawLitCost;
+        startPosition = anchor + cachedLitPrice->litlen;
+        assert(litlen >= cachedLitPrice->litlen);
+        remainingLength = litlen - cachedLitPrice->litlen;
+    } else {
+        startCost = 0;
+        startPosition = anchor;
+        remainingLength = litlen;
+    }
 
-    /* Return the last literals size */
-    return iend - anchor;
+    {   U32 const rawLitCost = startCost + ZSTD_rawLiteralsCost(startPosition, remainingLength, optStatePtr);
+        cachedLitPrice->anchor = anchor;
+        cachedLitPrice->litlen = litlen;
+        cachedLitPrice->rawLitCost = rawLitCost;
+        return rawLitCost;
+    }
 }
 
-
-size_t ZSTD_compressBlock_btopt(ZSTD_CCtx* ctx, const void* src, size_t srcSize)
+static U32 ZSTD_fullLiteralsCost_cached(
+                            cachedLiteralPrice_t* const cachedLitPrice,
+                            const BYTE* const anchor, U32 const litlen,
+                            const optState_t* const optStatePtr)
 {
-    return ZSTD_compressBlock_opt_generic(ctx, src, srcSize, 0);
+    return ZSTD_rawLiteralsCost_cached(cachedLitPrice, anchor, litlen, optStatePtr)
+         + ZSTD_litLengthPrice(litlen, optStatePtr);
 }
 
-size_t ZSTD_compressBlock_btultra(ZSTD_CCtx* ctx, const void* src, size_t srcSize)
+static int ZSTD_literalsContribution_cached(
+                            cachedLiteralPrice_t* const cachedLitPrice,
+                            const BYTE* const anchor, U32 const litlen,
+                            const optState_t* const optStatePtr)
 {
-    return ZSTD_compressBlock_opt_generic(ctx, src, srcSize, 1);
+    int const contribution = ZSTD_rawLiteralsCost_cached(cachedLitPrice, anchor, litlen, optStatePtr)
+                           + ZSTD_litLengthContribution(litlen, optStatePtr);
+    return contribution;
 }
 
-
 FORCE_INLINE_TEMPLATE
-size_t ZSTD_compressBlock_opt_extDict_generic(ZSTD_CCtx* ctx,
-                                     const void* src, size_t srcSize, const int ultra)
+size_t ZSTD_compressBlock_opt_generic(ZSTD_CCtx* ctx,
+                                      const void* src, size_t srcSize,
+                                      const int optLevel, const int extDict)
 {
-    seqStore_t* seqStorePtr = &(ctx->seqStore);
-    optState_t* optStatePtr = &(ctx->optState);
+    seqStore_t* const seqStorePtr = &(ctx->seqStore);
+    optState_t* const optStatePtr = &(ctx->optState);
     const BYTE* const istart = (const BYTE*)src;
     const BYTE* ip = istart;
     const BYTE* anchor = istart;
     const BYTE* const iend = istart + srcSize;
     const BYTE* const ilimit = iend - 8;
     const BYTE* const base = ctx->base;
-    const U32 lowestIndex = ctx->lowLimit;
-    const U32 dictLimit = ctx->dictLimit;
-    const BYTE* const prefixStart = base + dictLimit;
-    const BYTE* const dictBase = ctx->dictBase;
-    const BYTE* const dictEnd  = dictBase + dictLimit;
+    const BYTE* const prefixStart = base + ctx->dictLimit;
 
-    const U32 maxSearches = 1U << ctx->appliedParams.cParams.searchLog;
-    const U32 sufficient_len = ctx->appliedParams.cParams.targetLength;
-    const U32 mls = ctx->appliedParams.cParams.searchLength;
-    const U32 minMatch = (ctx->appliedParams.cParams.searchLength == 3) ? 3 : 4;
+    U32 const maxSearches = 1U << ctx->appliedParams.cParams.searchLog;
+    U32 const sufficient_len = MIN(ctx->appliedParams.cParams.targetLength, ZSTD_OPT_NUM -1);
+    U32 const mls = ctx->appliedParams.cParams.searchLength;
+    U32 const minMatch = (ctx->appliedParams.cParams.searchLength == 3) ? 3 : 4;
 
-    ZSTD_optimal_t* opt = optStatePtr->priceTable;
-    ZSTD_match_t* matches = optStatePtr->matchTable;
-    const BYTE* inr;
+    ZSTD_optimal_t* const opt = optStatePtr->priceTable;
+    ZSTD_match_t* const matches = optStatePtr->matchTable;
+    cachedLiteralPrice_t cachedLitPrice;
+    U32 rep[ZSTD_REP_NUM];
 
     /* init */
-    U32 offset, rep[ZSTD_REP_NUM];
-    { U32 i; for (i=0; i<ZSTD_REP_NUM; i++) rep[i]=seqStorePtr->rep[i]; }
-
+    DEBUGLOG(5, "ZSTD_compressBlock_opt_generic");
     ctx->nextToUpdate3 = ctx->nextToUpdate;
     ZSTD_rescaleFreqs(optStatePtr, (const BYTE*)src, srcSize);
     ip += (ip==prefixStart);
+    { int i; for (i=0; i<ZSTD_REP_NUM; i++) rep[i]=seqStorePtr->rep[i]; }
+    memset(&cachedLitPrice, 0, sizeof(cachedLitPrice));
 
     /* Match Loop */
     while (ip < ilimit) {
-        U32 cur, match_num, last_pos, litlen, price;
-        U32 u, mlen, best_mlen, best_off, litLength;
-        U32 current = (U32)(ip-base);
-        memset(opt, 0, sizeof(ZSTD_optimal_t));
-        last_pos = 0;
-        opt[0].litlen = (U32)(ip - anchor);
-
-        /* check repCode */
-        {   U32 i, last_i = ZSTD_REP_CHECK + (ip==anchor);
-            for (i = (ip==anchor); i<last_i; i++) {
-                const S32 repCur = (i==ZSTD_REP_MOVE_OPT) ? (rep[0] - 1) : rep[i];
-                const U32 repIndex = (U32)(current - repCur);
-                const BYTE* const repBase = repIndex < dictLimit ? dictBase : base;
-                const BYTE* const repMatch = repBase + repIndex;
-                if ( (repCur > 0 && repCur <= (S32)current)
-                   && (((U32)((dictLimit-1) - repIndex) >= 3) & (repIndex>lowestIndex))  /* intentional overflow */
-                   && (ZSTD_readMINMATCH(ip, minMatch) == ZSTD_readMINMATCH(repMatch, minMatch)) ) {
-                    /* repcode detected we should take it */
-                    const BYTE* const repEnd = repIndex < dictLimit ? dictEnd : iend;
-                    mlen = (U32)ZSTD_count_2segments(ip+minMatch, repMatch+minMatch, iend, repEnd, prefixStart) + minMatch;
-
-                    if (mlen > sufficient_len || mlen >= ZSTD_OPT_NUM) {
-                        best_mlen = mlen; best_off = i; cur = 0; last_pos = 1;
-                        goto _storeSequence;
-                    }
-
-                    best_off = i - (ip==anchor);
-                    litlen = opt[0].litlen;
-                    do {
-                        price = ZSTD_getPrice(optStatePtr, litlen, anchor, best_off, mlen - MINMATCH, ultra);
-                        if (mlen > last_pos || price < opt[mlen].price)
-                            SET_PRICE(mlen, mlen, i, litlen, price);   /* note : macro modifies last_pos */
-                        mlen--;
-                    } while (mlen >= minMatch);
-        }   }   }
-
-        match_num = ZSTD_BtGetAllMatches_selectMLS_extDict(ctx, ip, iend, maxSearches, mls, matches, minMatch);  /* first search (depth 0) */
-
-        if (!last_pos && !match_num) { ip++; continue; }
-
-        { U32 i; for (i=0; i<ZSTD_REP_NUM; i++) opt[0].rep[i] = rep[i]; }
-        opt[0].mlen = 1;
-
-        if (match_num && (matches[match_num-1].len > sufficient_len || matches[match_num-1].len >= ZSTD_OPT_NUM)) {
-            best_mlen = matches[match_num-1].len;
-            best_off = matches[match_num-1].off;
-            cur = 0;
-            last_pos = 1;
-            goto _storeSequence;
-        }
-
-        best_mlen = (last_pos) ? last_pos : minMatch;
-
-        /* set prices using matches at position = 0 */
-        for (u = 0; u < match_num; u++) {
-            mlen = (u>0) ? matches[u-1].len+1 : best_mlen;
-            best_mlen = matches[u].len;
-            litlen = opt[0].litlen;
-            while (mlen <= best_mlen) {
-                price = ZSTD_getPrice(optStatePtr, litlen, anchor, matches[u].off-1, mlen - MINMATCH, ultra);
-                if (mlen > last_pos || price < opt[mlen].price)
-                    SET_PRICE(mlen, mlen, matches[u].off, litlen, price);
-                mlen++;
-        }   }
-
-        if (last_pos < minMatch) {
-            ip++; continue;
+        U32 cur, last_pos = 0;
+        U32 best_mlen, best_off;
+
+        /* find first match */
+        {   U32 const litlen = (U32)(ip - anchor);
+            U32 const ll0 = !litlen;
+            U32 const nbMatches = ZSTD_BtGetAllMatches(ctx, ip, iend, extDict, maxSearches, mls, sufficient_len, rep, ll0, matches, minMatch);
+            if (!nbMatches) { ip++; continue; }
+
+            /* initialize opt[0] */
+            { U32 i ; for (i=0; i<ZSTD_REP_NUM; i++) opt[0].rep[i] = rep[i]; }
+            opt[0].mlen = 1;
+            opt[0].litlen = litlen;
+
+            /* large match -> immediate encoding */
+            {   U32 const maxML = matches[nbMatches-1].len;
+                DEBUGLOG(7, "found %u matches of maxLength=%u and offset=%u at cPos=%u => start new serie",
+                            nbMatches, maxML, matches[nbMatches-1].off, (U32)(ip-prefixStart));
+
+                if (maxML > sufficient_len) {
+                    best_mlen = maxML;
+                    best_off = matches[nbMatches-1].off;
+                    DEBUGLOG(7, "large match (%u>%u), immediate encoding",
+                                best_mlen, sufficient_len);
+                    cur = 0;
+                    last_pos = 1;
+                    goto _shortestPath;
+            }   }
+
+            /* set prices for first matches starting position == 0 */
+            {   U32 const literalsPrice = ZSTD_fullLiteralsCost_cached(&cachedLitPrice, anchor, litlen, optStatePtr);
+                U32 pos;
+                U32 matchNb;
+                for (pos = 0; pos < minMatch; pos++) {
+                    opt[pos].mlen = 1;
+                    opt[pos].price = ZSTD_MAX_PRICE;
+                }
+                for (matchNb = 0; matchNb < nbMatches; matchNb++) {
+                    U32 const offset = matches[matchNb].off;
+                    U32 const end = matches[matchNb].len;
+                    repcodes_t const repHistory = ZSTD_updateRep(rep, offset, ll0);
+                    for ( ; pos <= end ; pos++ ) {
+                        U32 const matchPrice = literalsPrice + ZSTD_getMatchPrice(offset, pos, optStatePtr, optLevel);
+                        DEBUGLOG(7, "rPos:%u => set initial price : %u",
+                                    pos, matchPrice);
+                        opt[pos].mlen = pos;
+                        opt[pos].off = offset;
+                        opt[pos].litlen = litlen;
+                        opt[pos].price = matchPrice;
+                        memcpy(opt[pos].rep, &repHistory, sizeof(repHistory));
+                }   }
+                last_pos = pos-1;
+            }
         }
 
         /* check further positions */
         for (cur = 1; cur <= last_pos; cur++) {
-            inr = ip + cur;
+            const BYTE* const inr = ip + cur;
+            assert(cur < ZSTD_OPT_NUM);
 
-            if (opt[cur-1].mlen == 1) {
-                litlen = opt[cur-1].litlen + 1;
+            /* Fix current position with one literal if cheaper */
+            {   U32 const litlen = (opt[cur-1].mlen == 1) ? opt[cur-1].litlen + 1 : 1;
+                int price;  /* note : contribution can be negative */
                 if (cur > litlen) {
-                    price = opt[cur - litlen].price + ZSTD_getLiteralPrice(optStatePtr, litlen, inr-litlen);
-                } else
-                    price = ZSTD_getLiteralPrice(optStatePtr, litlen, anchor);
-            } else {
-                litlen = 1;
-                price = opt[cur - 1].price + ZSTD_getLiteralPrice(optStatePtr, litlen, inr-1);
-            }
-
-            if (cur > last_pos || price <= opt[cur].price)
-                SET_PRICE(cur, 1, 0, litlen, price);
+                    price = opt[cur - litlen].price + ZSTD_literalsContribution(inr-litlen, litlen, optStatePtr);
+                } else {
+                    price = ZSTD_literalsContribution_cached(&cachedLitPrice, anchor, litlen, optStatePtr);
+                }
+                assert(price < 1000000000); /* overflow check */
+                if (price <= opt[cur].price) {
+                    DEBUGLOG(7, "rPos:%u : better price (%u<%u) using literal",
+                                cur, price, opt[cur].price);
+                    opt[cur].mlen = 1;
+                    opt[cur].off = 0;
+                    opt[cur].litlen = litlen;
+                    opt[cur].price = price;
+                    memcpy(opt[cur].rep, opt[cur-1].rep, sizeof(opt[cur].rep));
+            }   }
+
+            /* last match must start at a minimum distance of 8 from oend */
+            if (inr > ilimit) continue;
 
             if (cur == last_pos) break;
 
-            if (inr > ilimit)  /* last match must start at a minimum distance of 8 from oend */
-                continue;
-
-            mlen = opt[cur].mlen;
-            if (opt[cur].off > ZSTD_REP_MOVE_OPT) {
-                opt[cur].rep[2] = opt[cur-mlen].rep[1];
-                opt[cur].rep[1] = opt[cur-mlen].rep[0];
-                opt[cur].rep[0] = opt[cur].off - ZSTD_REP_MOVE_OPT;
-            } else {
-                opt[cur].rep[2] = (opt[cur].off > 1) ? opt[cur-mlen].rep[1] : opt[cur-mlen].rep[2];
-                opt[cur].rep[1] = (opt[cur].off > 0) ? opt[cur-mlen].rep[0] : opt[cur-mlen].rep[1];
-                assert(!(opt[cur].off == ZSTD_REP_MOVE_OPT && mlen == 1));
-                opt[cur].rep[0] = (opt[cur].off == ZSTD_REP_MOVE_OPT) ? (opt[cur-mlen].rep[0] - 1) : (opt[cur-mlen].rep[opt[cur].off]);
-            }
+             if ( (optLevel==0) /*static*/
+               && (opt[cur+1].price <= opt[cur].price) )
+                continue;  /* skip unpromising positions; about ~+6% speed, -0.01 ratio */
+
+            {   U32 const ll0 = (opt[cur].mlen != 1);
+                U32 const litlen = (opt[cur].mlen == 1) ? opt[cur].litlen : 0;
+                U32 const previousPrice = (cur > litlen) ? opt[cur-litlen].price : 0;
+                U32 const basePrice = previousPrice + ZSTD_fullLiteralsCost(inr-litlen, litlen, optStatePtr);
+                U32 const nbMatches = ZSTD_BtGetAllMatches(ctx, inr, iend, extDict, maxSearches, mls, sufficient_len, opt[cur].rep, ll0, matches, minMatch);
+                U32 matchNb;
+                if (!nbMatches) continue;
+
+                {   U32 const maxML = matches[nbMatches-1].len;
+                    DEBUGLOG(7, "rPos:%u, found %u matches, of maxLength=%u",
+                                cur, nbMatches, maxML);
+
+                    if ( (maxML > sufficient_len)
+                       | (cur + maxML >= ZSTD_OPT_NUM) ) {
+                        best_mlen = maxML;
+                        best_off = matches[nbMatches-1].off;
+                        last_pos = cur + 1;
+                        goto _shortestPath;
+                    }
+                }
 
-            best_mlen = minMatch;
-            {   U32 i, last_i = ZSTD_REP_CHECK + (mlen != 1);
-                for (i = (mlen != 1); i<last_i; i++) {
-                    const S32 repCur = (i==ZSTD_REP_MOVE_OPT) ? (opt[cur].rep[0] - 1) : opt[cur].rep[i];
-                    const U32 repIndex = (U32)(current+cur - repCur);
-                    const BYTE* const repBase = repIndex < dictLimit ? dictBase : base;
-                    const BYTE* const repMatch = repBase + repIndex;
-                    if ( (repCur > 0 && repCur <= (S32)(current+cur))
-                      && (((U32)((dictLimit-1) - repIndex) >= 3) & (repIndex>lowestIndex))  /* intentional overflow */
-                      && (ZSTD_readMINMATCH(inr, minMatch) == ZSTD_readMINMATCH(repMatch, minMatch)) ) {
-                        /* repcode detected */
-                        const BYTE* const repEnd = repIndex < dictLimit ? dictEnd : iend;
-                        mlen = (U32)ZSTD_count_2segments(inr+minMatch, repMatch+minMatch, iend, repEnd, prefixStart) + minMatch;
-
-                        if (mlen > sufficient_len || cur + mlen >= ZSTD_OPT_NUM) {
-                            best_mlen = mlen; best_off = i; last_pos = cur + 1;
-                            goto _storeSequence;
+                /* set prices using matches found at position == cur */
+                for (matchNb = 0; matchNb < nbMatches; matchNb++) {
+                    U32 const offset = matches[matchNb].off;
+                    repcodes_t const repHistory = ZSTD_updateRep(opt[cur].rep, offset, ll0);
+                    U32 const lastML = matches[matchNb].len;
+                    U32 const startML = (matchNb>0) ? matches[matchNb-1].len+1 : minMatch;
+                    U32 mlen;
+
+                    DEBUGLOG(7, "testing match %u => offCode=%u, mlen=%u, llen=%u",
+                                matchNb, matches[matchNb].off, lastML, litlen);
+
+                    for (mlen = lastML; mlen >= startML; mlen--) {
+                        U32 const pos = cur + mlen;
+                        int const price = basePrice + ZSTD_getMatchPrice(offset, mlen, optStatePtr, optLevel);
+
+                        if ((pos > last_pos) || (price < opt[pos].price)) {
+                            DEBUGLOG(7, "rPos:%u => new better price (%u<%u)",
+                                        pos, price, opt[pos].price);
+                            while (last_pos < pos) { opt[last_pos+1].price = ZSTD_MAX_PRICE; last_pos++; }
+                            opt[pos].mlen = mlen;
+                            opt[pos].off = offset;
+                            opt[pos].litlen = litlen;
+                            opt[pos].price = price;
+                            memcpy(opt[pos].rep, &repHistory, sizeof(repHistory));
+                        } else {
+                            if (optLevel==0) break;  /* gets ~+10% speed for about -0.01 ratio loss */
                         }
-
-                        best_off = i - (opt[cur].mlen != 1);
-                        if (mlen > best_mlen) best_mlen = mlen;
-
-                        do {
-                            if (opt[cur].mlen == 1) {
-                                litlen = opt[cur].litlen;
-                                if (cur > litlen) {
-                                    price = opt[cur - litlen].price + ZSTD_getPrice(optStatePtr, litlen, inr-litlen, best_off, mlen - MINMATCH, ultra);
-                                } else
-                                    price = ZSTD_getPrice(optStatePtr, litlen, anchor, best_off, mlen - MINMATCH, ultra);
-                            } else {
-                                litlen = 0;
-                                price = opt[cur].price + ZSTD_getPrice(optStatePtr, 0, NULL, best_off, mlen - MINMATCH, ultra);
-                            }
-
-                            if (cur + mlen > last_pos || price <= opt[cur + mlen].price)
-                                SET_PRICE(cur + mlen, mlen, i, litlen, price);
-                            mlen--;
-                        } while (mlen >= minMatch);
             }   }   }
-
-            match_num = ZSTD_BtGetAllMatches_selectMLS_extDict(ctx, inr, iend, maxSearches, mls, matches, minMatch);
-
-            if (match_num > 0 && (matches[match_num-1].len > sufficient_len || cur + matches[match_num-1].len >= ZSTD_OPT_NUM)) {
-                best_mlen = matches[match_num-1].len;
-                best_off = matches[match_num-1].off;
-                last_pos = cur + 1;
-                goto _storeSequence;
-            }
-
-            /* set prices using matches at position = cur */
-            for (u = 0; u < match_num; u++) {
-                mlen = (u>0) ? matches[u-1].len+1 : best_mlen;
-                best_mlen = matches[u].len;
-
-                while (mlen <= best_mlen) {
-                    if (opt[cur].mlen == 1) {
-                        litlen = opt[cur].litlen;
-                        if (cur > litlen)
-                            price = opt[cur - litlen].price + ZSTD_getPrice(optStatePtr, litlen, ip+cur-litlen, matches[u].off-1, mlen - MINMATCH, ultra);
-                        else
-                            price = ZSTD_getPrice(optStatePtr, litlen, anchor, matches[u].off-1, mlen - MINMATCH, ultra);
-                    } else {
-                        litlen = 0;
-                        price = opt[cur].price + ZSTD_getPrice(optStatePtr, 0, NULL, matches[u].off-1, mlen - MINMATCH, ultra);
-                    }
-
-                    if (cur + mlen > last_pos || (price < opt[cur + mlen].price))
-                        SET_PRICE(cur + mlen, mlen, matches[u].off, litlen, price);
-
-                    mlen++;
-        }   }   }   /* for (cur = 1; cur <= last_pos; cur++) */
+        }  /* for (cur = 1; cur <= last_pos; cur++) */
 
         best_mlen = opt[last_pos].mlen;
         best_off = opt[last_pos].off;
         cur = last_pos - best_mlen;
 
-        /* store sequence */
-_storeSequence:   /* cur, last_pos, best_mlen, best_off have to be set */
-        opt[0].mlen = 1;
-
-        while (1) {
-            mlen = opt[cur].mlen;
-            offset = opt[cur].off;
-            opt[cur].mlen = best_mlen;
-            opt[cur].off = best_off;
-            best_mlen = mlen;
-            best_off = offset;
-            if (mlen > cur) break;
-            cur -= mlen;
-        }
-
-        for (u = 0; u <= last_pos; ) {
-            u += opt[u].mlen;
-        }
+_shortestPath:   /* cur, last_pos, best_mlen, best_off have to be set */
+        assert(opt[0].mlen == 1);
+
+        /* reverse traversal */
+        DEBUGLOG(7, "start reverse traversal (last_pos:%u, cur:%u)",
+                    last_pos, cur);
+        {   U32 selectedMatchLength = best_mlen;
+            U32 selectedOffset = best_off;
+            U32 pos = cur;
+            while (1) {
+                U32 const mlen = opt[pos].mlen;
+                U32 const off = opt[pos].off;
+                opt[pos].mlen = selectedMatchLength;
+                opt[pos].off = selectedOffset;
+                selectedMatchLength = mlen;
+                selectedOffset = off;
+                if (mlen > pos) break;
+                pos -= mlen;
+        }   }
 
-        for (cur=0; cur < last_pos; ) {
-            mlen = opt[cur].mlen;
-            if (mlen == 1) { ip++; cur++; continue; }
-            offset = opt[cur].off;
-            cur += mlen;
-            litLength = (U32)(ip - anchor);
-
-            if (offset > ZSTD_REP_MOVE_OPT) {
-                rep[2] = rep[1];
-                rep[1] = rep[0];
-                rep[0] = offset - ZSTD_REP_MOVE_OPT;
-                offset--;
-            } else {
-                if (offset != 0) {
-                    best_off = (offset==ZSTD_REP_MOVE_OPT) ? (rep[0] - 1) : (rep[offset]);
-                    if (offset != 1) rep[2] = rep[1];
+        /* save sequences */
+        {   U32 pos;
+            for (pos=0; pos < last_pos; ) {
+                U32 const llen = (U32)(ip - anchor);
+                U32 const mlen = opt[pos].mlen;
+                U32 const offset = opt[pos].off;
+                if (mlen == 1) { ip++; pos++; continue; }  /* literal position => move on */
+                pos += mlen; ip += mlen;
+
+                /* repcodes update : like ZSTD_updateRep(), but update in place */
+                if (offset >= ZSTD_REP_NUM) {  /* full offset */
+                    rep[2] = rep[1];
                     rep[1] = rep[0];
-                    rep[0] = best_off;
+                    rep[0] = offset - ZSTD_REP_MOVE;
+                } else {   /* repcode */
+                    U32 const repCode = offset + (llen==0);
+                    if (repCode) {  /* note : if repCode==0, no change */
+                        U32 const currentOffset = (repCode==ZSTD_REP_NUM) ? (rep[0] - 1) : rep[repCode];
+                        if (repCode >= 2) rep[2] = rep[1];
+                        rep[1] = rep[0];
+                        rep[0] = currentOffset;
+                    }
                 }
 
-                if (litLength==0) offset--;
-            }
-
-            ZSTD_updatePrice(optStatePtr, litLength, anchor, offset, mlen-MINMATCH);
-            ZSTD_storeSeq(seqStorePtr, litLength, anchor, offset, mlen-MINMATCH);
-            anchor = ip = ip + mlen;
-    }    }   /* for (cur=0; cur < last_pos; ) */
+                ZSTD_updateStats(optStatePtr, llen, anchor, offset, mlen);
+                ZSTD_storeSeq(seqStorePtr, llen, anchor, offset, mlen-MINMATCH);
+                anchor = ip;
+        }   }
+        ZSTD_setLog2Prices(optStatePtr);
+    }   /* while (ip < ilimit) */
 
     /* Save reps for next block */
     { int i; for (i=0; i<ZSTD_REP_NUM; i++) seqStorePtr->repToConfirm[i] = rep[i]; }
@@ -946,12 +763,23 @@ _storeSequence:   /* cur, last_pos, best_mlen, best_off have to be set */
 }
 
 
+size_t ZSTD_compressBlock_btopt(ZSTD_CCtx* ctx, const void* src, size_t srcSize)
+{
+    DEBUGLOG(5, "ZSTD_compressBlock_btopt");
+    return ZSTD_compressBlock_opt_generic(ctx, src, srcSize, 0 /*optLevel*/, 0 /*extDict*/);
+}
+
+size_t ZSTD_compressBlock_btultra(ZSTD_CCtx* ctx, const void* src, size_t srcSize)
+{
+    return ZSTD_compressBlock_opt_generic(ctx, src, srcSize, 2 /*optLevel*/, 0 /*extDict*/);
+}
+
 size_t ZSTD_compressBlock_btopt_extDict(ZSTD_CCtx* ctx, const void* src, size_t srcSize)
 {
-    return ZSTD_compressBlock_opt_extDict_generic(ctx, src, srcSize, 0);
+    return ZSTD_compressBlock_opt_generic(ctx, src, srcSize, 0 /*optLevel*/, 1 /*extDict*/);
 }
 
 size_t ZSTD_compressBlock_btultra_extDict(ZSTD_CCtx* ctx, const void* src, size_t srcSize)
 {
-    return ZSTD_compressBlock_opt_extDict_generic(ctx, src, srcSize, 1);
+    return ZSTD_compressBlock_opt_generic(ctx, src, srcSize, 2 /*optLevel*/, 1 /*extDict*/);
 }
diff --git a/thirdparty/zstd/compress/zstd_opt.h b/thirdparty/zstd/compress/zstd_opt.h
index 816a1fabbf..82e810c293 100644
--- a/thirdparty/zstd/compress/zstd_opt.h
+++ b/thirdparty/zstd/compress/zstd_opt.h
@@ -11,12 +11,12 @@
 #ifndef ZSTD_OPT_H
 #define ZSTD_OPT_H
 
-#include "zstd_compress.h"
-
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
+#include "zstd.h"   /* ZSTD_CCtx, size_t */
+
 size_t ZSTD_compressBlock_btopt(ZSTD_CCtx* ctx, const void* src, size_t srcSize);
 size_t ZSTD_compressBlock_btultra(ZSTD_CCtx* ctx, const void* src, size_t srcSize);
 
diff --git a/thirdparty/zstd/compress/zstdmt_compress.c b/thirdparty/zstd/compress/zstdmt_compress.c
index 7831cd3bd8..e51edf124f 100644
--- a/thirdparty/zstd/compress/zstdmt_compress.c
+++ b/thirdparty/zstd/compress/zstdmt_compress.c
@@ -24,7 +24,7 @@
 #include <string.h>      /* memcpy, memset */
 #include "pool.h"        /* threadpool */
 #include "threading.h"   /* mutex */
-#include "zstd_internal.h"  /* MIN, ERROR, ZSTD_*, ZSTD_highbit32 */
+#include "zstd_compress_internal.h"  /* MIN, ERROR, ZSTD_*, ZSTD_highbit32 */
 #include "zstdmt_compress.h"
 
 
@@ -140,9 +140,12 @@ static size_t ZSTDMT_sizeof_bufferPool(ZSTDMT_bufferPool* bufPool)
     return poolSize + totalBufferSize;
 }
 
-static void ZSTDMT_setBufferSize(ZSTDMT_bufferPool* bufPool, size_t bSize)
+static void ZSTDMT_setBufferSize(ZSTDMT_bufferPool* const bufPool, size_t const bSize)
 {
+    ZSTD_pthread_mutex_lock(&bufPool->poolMutex);
+    DEBUGLOG(4, "ZSTDMT_setBufferSize: bSize = %u", (U32)bSize);
     bufPool->bufferSize = bSize;
+    ZSTD_pthread_mutex_unlock(&bufPool->poolMutex);
 }
 
 /** ZSTDMT_getBuffer() :
@@ -150,28 +153,31 @@ static void ZSTDMT_setBufferSize(ZSTDMT_bufferPool* bufPool, size_t bSize)
 static buffer_t ZSTDMT_getBuffer(ZSTDMT_bufferPool* bufPool)
 {
     size_t const bSize = bufPool->bufferSize;
-    DEBUGLOG(5, "ZSTDMT_getBuffer");
+    DEBUGLOG(5, "ZSTDMT_getBuffer: bSize = %u", (U32)bufPool->bufferSize);
     ZSTD_pthread_mutex_lock(&bufPool->poolMutex);
     if (bufPool->nbBuffers) {   /* try to use an existing buffer */
         buffer_t const buf = bufPool->bTable[--(bufPool->nbBuffers)];
         size_t const availBufferSize = buf.size;
         bufPool->bTable[bufPool->nbBuffers] = g_nullBuffer;
-        if ((availBufferSize >= bSize) & (availBufferSize <= 10*bSize)) {
+        if ((availBufferSize >= bSize) & ((availBufferSize>>3) <= bSize)) {
             /* large enough, but not too much */
+            DEBUGLOG(5, "ZSTDMT_getBuffer: provide buffer %u of size %u",
+                        bufPool->nbBuffers, (U32)buf.size);
             ZSTD_pthread_mutex_unlock(&bufPool->poolMutex);
             return buf;
         }
         /* size conditions not respected : scratch this buffer, create new one */
-        DEBUGLOG(5, "existing buffer does not meet size conditions => freeing");
+        DEBUGLOG(5, "ZSTDMT_getBuffer: existing buffer does not meet size conditions => freeing");
         ZSTD_free(buf.start, bufPool->cMem);
     }
     ZSTD_pthread_mutex_unlock(&bufPool->poolMutex);
     /* create new buffer */
-    DEBUGLOG(5, "create a new buffer");
+    DEBUGLOG(5, "ZSTDMT_getBuffer: create a new buffer");
     {   buffer_t buffer;
         void* const start = ZSTD_malloc(bSize, bufPool->cMem);
         buffer.start = start;   /* note : start can be NULL if malloc fails ! */
         buffer.size = (start==NULL) ? 0 : bSize;
+        DEBUGLOG(5, "ZSTDMT_getBuffer: created buffer of size %u", (U32)bSize);
         return buffer;
     }
 }
@@ -184,12 +190,14 @@ static void ZSTDMT_releaseBuffer(ZSTDMT_bufferPool* bufPool, buffer_t buf)
     ZSTD_pthread_mutex_lock(&bufPool->poolMutex);
     if (bufPool->nbBuffers < bufPool->totalBuffers) {
         bufPool->bTable[bufPool->nbBuffers++] = buf;  /* stored for later use */
+        DEBUGLOG(5, "ZSTDMT_releaseBuffer: stored buffer of size %u in slot %u",
+                    (U32)buf.size, (U32)(bufPool->nbBuffers-1));
         ZSTD_pthread_mutex_unlock(&bufPool->poolMutex);
         return;
     }
     ZSTD_pthread_mutex_unlock(&bufPool->poolMutex);
     /* Reached bufferPool capacity (should not happen) */
-    DEBUGLOG(5, "buffer pool capacity reached => freeing ");
+    DEBUGLOG(5, "ZSTDMT_releaseBuffer: pool capacity reached => freeing ");
     ZSTD_free(buf.start, bufPool->cMem);
 }
 
@@ -302,7 +310,7 @@ static void ZSTDMT_releaseCCtx(ZSTDMT_CCtxPool* pool, ZSTD_CCtx* cctx)
 typedef struct {
     buffer_t src;
     const void* srcStart;
-    size_t   dictSize;
+    size_t   prefixSize;
     size_t   srcSize;
     buffer_t dstBuff;
     size_t   cSize;
@@ -324,11 +332,11 @@ typedef struct {
 void ZSTDMT_compressChunk(void* jobDescription)
 {
     ZSTDMT_jobDescription* const job = (ZSTDMT_jobDescription*)jobDescription;
-    ZSTD_CCtx* cctx = ZSTDMT_getCCtx(job->cctxPool);
-    const void* const src = (const char*)job->srcStart + job->dictSize;
+    ZSTD_CCtx* const cctx = ZSTDMT_getCCtx(job->cctxPool);
+    const void* const src = (const char*)job->srcStart + job->prefixSize;
     buffer_t dstBuff = job->dstBuff;
-    DEBUGLOG(5, "job (first:%u) (last:%u) : dictSize %u, srcSize %u",
-                 job->firstChunk, job->lastChunk, (U32)job->dictSize, (U32)job->srcSize);
+    DEBUGLOG(5, "ZSTDMT_compressChunk: job (first:%u) (last:%u) : prefixSize %u, srcSize %u ",
+                 job->firstChunk, job->lastChunk, (U32)job->prefixSize, (U32)job->srcSize);
 
     if (cctx==NULL) {
         job->cSize = ERROR(memory_allocation);
@@ -342,38 +350,48 @@ void ZSTDMT_compressChunk(void* jobDescription)
             goto _endJob;
         }
         job->dstBuff = dstBuff;
+        DEBUGLOG(5, "ZSTDMT_compressChunk: received dstBuff of size %u", (U32)dstBuff.size);
     }
 
-    if (job->cdict) {  /* should only happen for first segment */
-        size_t const initError = ZSTD_compressBegin_usingCDict_advanced(cctx, job->cdict, job->params.fParams, job->fullFrameSize);
-        DEBUGLOG(5, "using CDict");
+    if (job->cdict) {
+        size_t const initError = ZSTD_compressBegin_advanced_internal(cctx, NULL, 0, ZSTD_dm_auto, job->cdict, job->params, job->fullFrameSize);
+        DEBUGLOG(4, "ZSTDMT_compressChunk: init using CDict (windowLog=%u)", job->params.cParams.windowLog);
+        assert(job->firstChunk);  /* only allowed for first job */
         if (ZSTD_isError(initError)) { job->cSize = initError; goto _endJob; }
     } else {  /* srcStart points at reloaded section */
-        if (!job->firstChunk) job->params.fParams.contentSizeFlag = 0;  /* ensure no srcSize control */
-        { ZSTD_CCtx_params jobParams = job->params;
-          size_t const forceWindowError =
-              ZSTD_CCtxParam_setParameter(&jobParams, ZSTD_p_forceMaxWindow, !job->firstChunk);
-          /* Force loading dictionary in "content-only" mode (no header analysis) */
-          size_t const initError = ZSTD_compressBegin_advanced_internal(cctx, job->srcStart, job->dictSize, ZSTD_dm_rawContent, jobParams, job->fullFrameSize);
-            if (ZSTD_isError(initError) || ZSTD_isError(forceWindowError)) {
+        U64 const pledgedSrcSize = job->firstChunk ? job->fullFrameSize : ZSTD_CONTENTSIZE_UNKNOWN;
+        ZSTD_CCtx_params jobParams = job->params;   /* do not modify job->params ! copy it, modify the copy */
+        size_t const forceWindowError = ZSTD_CCtxParam_setParameter(&jobParams, ZSTD_p_forceMaxWindow, !job->firstChunk);
+        if (ZSTD_isError(forceWindowError)) {
+            DEBUGLOG(5, "ZSTD_CCtxParam_setParameter error : %s ", ZSTD_getErrorName(forceWindowError));
+            job->cSize = forceWindowError;
+            goto _endJob;
+        }
+        DEBUGLOG(5, "ZSTDMT_compressChunk: invoking ZSTD_compressBegin_advanced_internal with windowLog = %u ", jobParams.cParams.windowLog);
+        {   size_t const initError = ZSTD_compressBegin_advanced_internal(cctx,
+                                        job->srcStart, job->prefixSize, ZSTD_dm_rawContent, /* load dictionary in "content-only" mode (no header analysis) */
+                                        NULL,
+                                        jobParams, pledgedSrcSize);
+            if (ZSTD_isError(initError)) {
+                DEBUGLOG(5, "ZSTD_compressBegin_advanced_internal error : %s ", ZSTD_getErrorName(initError));
                 job->cSize = initError;
                 goto _endJob;
-            }
-    }   }
-    if (!job->firstChunk) {  /* flush and overwrite frame header when it's not first segment */
+        }   }
+    }
+    if (!job->firstChunk) {  /* flush and overwrite frame header when it's not first job */
         size_t const hSize = ZSTD_compressContinue(cctx, dstBuff.start, dstBuff.size, src, 0);
-        if (ZSTD_isError(hSize)) { job->cSize = hSize; goto _endJob; }
+        if (ZSTD_isError(hSize)) { job->cSize = hSize; /* save error code */ goto _endJob; }
         ZSTD_invalidateRepCodes(cctx);
     }
 
-    DEBUGLOG(5, "Compressing : ");
-    DEBUG_PRINTHEX(4, job->srcStart, 12);
+    DEBUGLOG(5, "Compressing into dstBuff of size %u", (U32)dstBuff.size);
+    DEBUG_PRINTHEX(6, job->srcStart, 12);
     job->cSize = (job->lastChunk) ?
                  ZSTD_compressEnd     (cctx, dstBuff.start, dstBuff.size, src, job->srcSize) :
                  ZSTD_compressContinue(cctx, dstBuff.start, dstBuff.size, src, job->srcSize);
-    DEBUGLOG(5, "compressed %u bytes into %u bytes   (first:%u) (last:%u)",
+    DEBUGLOG(5, "compressed %u bytes into %u bytes   (first:%u) (last:%u) ",
                 (unsigned)job->srcSize, (unsigned)job->cSize, job->firstChunk, job->lastChunk);
-    DEBUGLOG(5, "dstBuff.size : %u ; => %s", (U32)dstBuff.size, ZSTD_getErrorName(job->cSize));
+    DEBUGLOG(5, "dstBuff.size : %u ; => %s ", (U32)dstBuff.size, ZSTD_getErrorName(job->cSize));
 
 _endJob:
     ZSTDMT_releaseCCtx(job->cctxPool, cctx);
@@ -403,13 +421,14 @@ struct ZSTDMT_CCtx_s {
     ZSTDMT_CCtxPool* cctxPool;
     ZSTD_pthread_mutex_t jobCompleted_mutex;
     ZSTD_pthread_cond_t jobCompleted_cond;
+    ZSTD_CCtx_params params;
     size_t targetSectionSize;
     size_t inBuffSize;
     size_t dictSize;
     size_t targetDictSize;
     inBuff_t inBuff;
-    ZSTD_CCtx_params params;
     XXH64_state_t xxhState;
+    unsigned singleThreaded;
     unsigned jobIDMask;
     unsigned doneJobID;
     unsigned nextJobID;
@@ -430,20 +449,32 @@ static ZSTDMT_jobDescription* ZSTDMT_allocJobsTable(U32* nbJobsPtr, ZSTD_customM
                             nbJobs * sizeof(ZSTDMT_jobDescription), cMem);
 }
 
-/* Internal only */
-size_t ZSTDMT_initializeCCtxParameters(ZSTD_CCtx_params* params, unsigned nbThreads)
+/* ZSTDMT_CCtxParam_setNbThreads():
+ * Internal use only */
+size_t ZSTDMT_CCtxParam_setNbThreads(ZSTD_CCtx_params* params, unsigned nbThreads)
 {
+    if (nbThreads > ZSTDMT_NBTHREADS_MAX) nbThreads = ZSTDMT_NBTHREADS_MAX;
+    if (nbThreads < 1) nbThreads = 1;
     params->nbThreads = nbThreads;
     params->overlapSizeLog = ZSTDMT_OVERLAPLOG_DEFAULT;
     params->jobSize = 0;
-    return 0;
+    return nbThreads;
+}
+
+/* ZSTDMT_getNbThreads():
+ * @return nb threads currently active in mtctx.
+ * mtctx must be valid */
+size_t ZSTDMT_getNbThreads(const ZSTDMT_CCtx* mtctx)
+{
+    assert(mtctx != NULL);
+    return mtctx->params.nbThreads;
 }
 
 ZSTDMT_CCtx* ZSTDMT_createCCtx_advanced(unsigned nbThreads, ZSTD_customMem cMem)
 {
     ZSTDMT_CCtx* mtctx;
     U32 nbJobs = nbThreads + 2;
-    DEBUGLOG(3, "ZSTDMT_createCCtx_advanced");
+    DEBUGLOG(3, "ZSTDMT_createCCtx_advanced (nbThreads = %u)", nbThreads);
 
     if (nbThreads < 1) return NULL;
     nbThreads = MIN(nbThreads , ZSTDMT_NBTHREADS_MAX);
@@ -453,7 +484,7 @@ ZSTDMT_CCtx* ZSTDMT_createCCtx_advanced(unsigned nbThreads, ZSTD_customMem cMem)
 
     mtctx = (ZSTDMT_CCtx*) ZSTD_calloc(sizeof(ZSTDMT_CCtx), cMem);
     if (!mtctx) return NULL;
-    ZSTDMT_initializeCCtxParameters(&mtctx->params, nbThreads);
+    ZSTDMT_CCtxParam_setNbThreads(&mtctx->params, nbThreads);
     mtctx->cMem = cMem;
     mtctx->allJobsCompleted = 1;
     mtctx->factory = POOL_create_advanced(nbThreads, 0, cMem);
@@ -545,17 +576,23 @@ size_t ZSTDMT_sizeof_CCtx(ZSTDMT_CCtx* mtctx)
 }
 
 /* Internal only */
-size_t ZSTDMT_CCtxParam_setMTCtxParameter(
-    ZSTD_CCtx_params* params, ZSTDMT_parameter parameter, unsigned value) {
+size_t ZSTDMT_CCtxParam_setMTCtxParameter(ZSTD_CCtx_params* params,
+                                ZSTDMT_parameter parameter, unsigned value) {
+    DEBUGLOG(4, "ZSTDMT_CCtxParam_setMTCtxParameter");
     switch(parameter)
     {
-    case ZSTDMT_p_sectionSize :
+    case ZSTDMT_p_jobSize :
+        DEBUGLOG(4, "ZSTDMT_CCtxParam_setMTCtxParameter : set jobSize to %u", value);
+        if ( (value > 0)  /* value==0 => automatic job size */
+           & (value < ZSTDMT_JOBSIZE_MIN) )
+            value = ZSTDMT_JOBSIZE_MIN;
         params->jobSize = value;
-        return 0;
+        return value;
     case ZSTDMT_p_overlapSectionLog :
+        if (value > 9) value = 9;
         DEBUGLOG(4, "ZSTDMT_p_overlapSectionLog : %u", value);
         params->overlapSizeLog = (value >= 9) ? 9 : value;
-        return 0;
+        return value;
     default :
         return ERROR(parameter_unsupported);
     }
@@ -563,9 +600,10 @@ size_t ZSTDMT_CCtxParam_setMTCtxParameter(
 
 size_t ZSTDMT_setMTCtxParameter(ZSTDMT_CCtx* mtctx, ZSTDMT_parameter parameter, unsigned value)
 {
+    DEBUGLOG(4, "ZSTDMT_setMTCtxParameter");
     switch(parameter)
     {
-    case ZSTDMT_p_sectionSize :
+    case ZSTDMT_p_jobSize :
         return ZSTDMT_CCtxParam_setMTCtxParameter(&mtctx->params, parameter, value);
     case ZSTDMT_p_overlapSectionLog :
         return ZSTDMT_CCtxParam_setMTCtxParameter(&mtctx->params, parameter, value);
@@ -601,7 +639,7 @@ static size_t ZSTDMT_compress_advanced_internal(
     size_t const overlapSize = (overlapRLog>=9) ? 0 : (size_t)1 << (params.cParams.windowLog - overlapRLog);
     unsigned nbChunks = computeNbChunks(srcSize, params.cParams.windowLog, params.nbThreads);
     size_t const proposedChunkSize = (srcSize + (nbChunks-1)) / nbChunks;
-    size_t const avgChunkSize = ((proposedChunkSize & 0x1FFFF) < 0x7FFF) ? proposedChunkSize + 0xFFFF : proposedChunkSize;   /* avoid too small last block */
+    size_t const avgChunkSize = (((proposedChunkSize-1) & 0x1FFFF) < 0x7FFF) ? proposedChunkSize + 0xFFFF : proposedChunkSize;   /* avoid too small last block */
     const char* const srcStart = (const char*)src;
     size_t remainingSrcSize = srcSize;
     unsigned const compressWithinDst = (dstCapacity >= ZSTD_compressBound(srcSize)) ? nbChunks : (unsigned)(dstCapacity / ZSTD_compressBound(avgChunkSize));  /* presumes avgChunkSize >= 256 KB, which should be the case */
@@ -610,7 +648,8 @@ static size_t ZSTDMT_compress_advanced_internal(
     assert(jobParams.nbThreads == 0);
     assert(mtctx->cctxPool->totalCCtx == params.nbThreads);
 
-    DEBUGLOG(4, "nbChunks  : %2u   (chunkSize : %u bytes)   ", nbChunks, (U32)avgChunkSize);
+    DEBUGLOG(4, "ZSTDMT_compress_advanced_internal: nbChunks=%2u (rawSize=%u bytes; fixedSize=%u)  ",
+                nbChunks, (U32)proposedChunkSize, (U32)avgChunkSize);
     if (nbChunks==1) {   /* fallback to single-thread mode */
         ZSTD_CCtx* const cctx = mtctx->cctxPool->cctx[0];
         if (cdict) return ZSTD_compress_usingCDict_advanced(cctx, dst, dstCapacity, src, srcSize, cdict, jobParams.fParams);
@@ -639,9 +678,9 @@ static size_t ZSTDMT_compress_advanced_internal(
 
             mtctx->jobs[u].src = g_nullBuffer;
             mtctx->jobs[u].srcStart = srcStart + frameStartPos - dictSize;
-            mtctx->jobs[u].dictSize = dictSize;
+            mtctx->jobs[u].prefixSize = dictSize;
             mtctx->jobs[u].srcSize = chunkSize;
-            mtctx->jobs[u].cdict = mtctx->nextJobID==0 ? cdict : NULL;
+            mtctx->jobs[u].cdict = (u==0) ? cdict : NULL;
             mtctx->jobs[u].fullFrameSize = srcSize;
             mtctx->jobs[u].params = jobParams;
             /* do not calculate checksum within sections, but write it in header for first section */
@@ -659,7 +698,7 @@ static size_t ZSTDMT_compress_advanced_internal(
                 XXH64_update(&xxh64, srcStart + frameStartPos, chunkSize);
             }
 
-            DEBUGLOG(5, "posting job %u   (%u bytes)", u, (U32)chunkSize);
+            DEBUGLOG(5, "ZSTDMT_compress_advanced_internal: posting job %u  (%u bytes)", u, (U32)chunkSize);
             DEBUG_PRINTHEX(6, mtctx->jobs[u].srcStart, 12);
             POOL_add(mtctx->factory, ZSTDMT_compressChunk, &mtctx->jobs[u]);
 
@@ -753,13 +792,14 @@ size_t ZSTDMT_initCStream_internal(
         const ZSTD_CDict* cdict, ZSTD_CCtx_params params,
         unsigned long long pledgedSrcSize)
 {
-    DEBUGLOG(4, "ZSTDMT_initCStream_internal");
+    DEBUGLOG(4, "ZSTDMT_initCStream_internal (pledgedSrcSize=%u)", (U32)pledgedSrcSize);
     /* params are supposed to be fully validated at this point */
     assert(!ZSTD_isError(ZSTD_checkCParams(params.cParams)));
     assert(!((dict) && (cdict)));  /* either dict or cdict, not both */
     assert(zcs->cctxPool->totalCCtx == params.nbThreads);
+    zcs->singleThreaded = (params.nbThreads==1) | (pledgedSrcSize <= ZSTDMT_JOBSIZE_MIN);  /* do not trigger multi-threading when srcSize is too small */
 
-    if (params.nbThreads==1) {
+    if (zcs->singleThreaded) {
         ZSTD_CCtx_params const singleThreadParams = ZSTDMT_makeJobCCtxParams(params);
         DEBUGLOG(4, "single thread mode");
         assert(singleThreadParams.nbThreads == 0);
@@ -767,6 +807,7 @@ size_t ZSTDMT_initCStream_internal(
                                          dict, dictSize, cdict,
                                          singleThreadParams, pledgedSrcSize);
     }
+    DEBUGLOG(4, "multi-threading mode (%u threads)", params.nbThreads);
 
     if (zcs->allJobsCompleted == 0) {   /* previous compression not correctly finished */
         ZSTDMT_waitForAllJobsCompleted(zcs);
@@ -777,7 +818,6 @@ size_t ZSTDMT_initCStream_internal(
     zcs->params = params;
     zcs->frameContentSize = pledgedSrcSize;
     if (dict) {
-        DEBUGLOG(4,"cdictLocal: %08X", (U32)(size_t)zcs->cdictLocal);
         ZSTD_freeCDict(zcs->cdictLocal);
         zcs->cdictLocal = ZSTD_createCDict_advanced(dict, dictSize,
                                                     ZSTD_dlm_byCopy, dictMode, /* note : a loadPrefix becomes an internal CDict */
@@ -785,20 +825,20 @@ size_t ZSTDMT_initCStream_internal(
         zcs->cdict = zcs->cdictLocal;
         if (zcs->cdictLocal == NULL) return ERROR(memory_allocation);
     } else {
-        DEBUGLOG(4,"cdictLocal: %08X", (U32)(size_t)zcs->cdictLocal);
         ZSTD_freeCDict(zcs->cdictLocal);
         zcs->cdictLocal = NULL;
         zcs->cdict = cdict;
     }
 
+    assert(params.overlapSizeLog <= 9);
     zcs->targetDictSize = (params.overlapSizeLog==0) ? 0 : (size_t)1 << (params.cParams.windowLog - (9 - params.overlapSizeLog));
-    DEBUGLOG(4, "overlapLog : %u ", params.overlapSizeLog);
-    DEBUGLOG(4, "overlap Size : %u KB", (U32)(zcs->targetDictSize>>10));
+    DEBUGLOG(4, "overlapLog=%u => %u KB", params.overlapSizeLog, (U32)(zcs->targetDictSize>>10));
     zcs->targetSectionSize = params.jobSize ? params.jobSize : (size_t)1 << (params.cParams.windowLog + 2);
-    zcs->targetSectionSize = MAX(ZSTDMT_SECTION_SIZE_MIN, zcs->targetSectionSize);
-    zcs->targetSectionSize = MAX(zcs->targetDictSize, zcs->targetSectionSize);
-    DEBUGLOG(4, "Section Size : %u KB", (U32)(zcs->targetSectionSize>>10));
+    if (zcs->targetSectionSize < ZSTDMT_JOBSIZE_MIN) zcs->targetSectionSize = ZSTDMT_JOBSIZE_MIN;
+    if (zcs->targetSectionSize < zcs->targetDictSize) zcs->targetSectionSize = zcs->targetDictSize;  /* job size must be >= overlap size */
+    DEBUGLOG(4, "Job Size : %u KB (note : set to %u)", (U32)(zcs->targetSectionSize>>10), params.jobSize);
     zcs->inBuffSize = zcs->targetDictSize + zcs->targetSectionSize;
+    DEBUGLOG(4, "inBuff Size : %u KB", (U32)(zcs->inBuffSize>>10));
     ZSTDMT_setBufferSize(zcs->bufPool, MAX(zcs->inBuffSize, ZSTD_compressBound(zcs->targetSectionSize)) );
     zcs->inBuff.buffer = g_nullBuffer;
     zcs->dictSize = 0;
@@ -816,7 +856,7 @@ size_t ZSTDMT_initCStream_advanced(ZSTDMT_CCtx* mtctx,
                                    unsigned long long pledgedSrcSize)
 {
     ZSTD_CCtx_params cctxParams = mtctx->params;
-    DEBUGLOG(5, "ZSTDMT_initCStream_advanced");
+    DEBUGLOG(5, "ZSTDMT_initCStream_advanced (pledgedSrcSize=%u)", (U32)pledgedSrcSize);
     cctxParams.cParams = params.cParams;
     cctxParams.fParams = params.fParams;
     return ZSTDMT_initCStream_internal(mtctx, dict, dictSize, ZSTD_dm_auto, NULL,
@@ -838,9 +878,12 @@ size_t ZSTDMT_initCStream_usingCDict(ZSTDMT_CCtx* mtctx,
 
 
 /* ZSTDMT_resetCStream() :
- * pledgedSrcSize is optional and can be zero == unknown */
+ * pledgedSrcSize can be zero == unknown (for the time being)
+ * prefer using ZSTD_CONTENTSIZE_UNKNOWN,
+ * as `0` might mean "empty" in the future */
 size_t ZSTDMT_resetCStream(ZSTDMT_CCtx* zcs, unsigned long long pledgedSrcSize)
 {
+    if (!pledgedSrcSize) pledgedSrcSize = ZSTD_CONTENTSIZE_UNKNOWN;
     if (zcs->params.nbThreads==1)
         return ZSTD_resetCStream(zcs->cctxPool->cctx[0], pledgedSrcSize);
     return ZSTDMT_initCStream_internal(zcs, NULL, 0, ZSTD_dm_auto, 0, zcs->params,
@@ -852,7 +895,7 @@ size_t ZSTDMT_initCStream(ZSTDMT_CCtx* zcs, int compressionLevel) {
     ZSTD_CCtx_params cctxParams = zcs->params;
     cctxParams.cParams = params.cParams;
     cctxParams.fParams = params.fParams;
-    return ZSTDMT_initCStream_internal(zcs, NULL, 0, ZSTD_dm_auto, NULL, cctxParams, 0);
+    return ZSTDMT_initCStream_internal(zcs, NULL, 0, ZSTD_dm_auto, NULL, cctxParams, ZSTD_CONTENTSIZE_UNKNOWN);
 }
 
 
@@ -860,12 +903,12 @@ static size_t ZSTDMT_createCompressionJob(ZSTDMT_CCtx* zcs, size_t srcSize, unsi
 {
     unsigned const jobID = zcs->nextJobID & zcs->jobIDMask;
 
-    DEBUGLOG(4, "preparing job %u to compress %u bytes with %u preload ",
+    DEBUGLOG(5, "ZSTDMT_createCompressionJob: preparing job %u to compress %u bytes with %u preload ",
                 zcs->nextJobID, (U32)srcSize, (U32)zcs->dictSize);
     zcs->jobs[jobID].src = zcs->inBuff.buffer;
     zcs->jobs[jobID].srcStart = zcs->inBuff.buffer.start;
     zcs->jobs[jobID].srcSize = srcSize;
-    zcs->jobs[jobID].dictSize = zcs->dictSize;
+    zcs->jobs[jobID].prefixSize = zcs->dictSize;
     assert(zcs->inBuff.filled >= srcSize + zcs->dictSize);
     zcs->jobs[jobID].params = zcs->params;
     /* do not calculate checksum within sections, but write it in header for first section */
@@ -911,7 +954,7 @@ static size_t ZSTDMT_createCompressionJob(ZSTDMT_CCtx* zcs, size_t srcSize, unsi
             zcs->params.fParams.checksumFlag = 0;
     }   }
 
-    DEBUGLOG(4, "posting job %u : %u bytes  (end:%u) (note : doneJob = %u=>%u)",
+    DEBUGLOG(5, "ZSTDMT_createCompressionJob: posting job %u : %u bytes  (end:%u) (note : doneJob = %u=>%u)",
                 zcs->nextJobID,
                 (U32)zcs->jobs[jobID].srcSize,
                 zcs->jobs[jobID].lastChunk,
@@ -930,6 +973,7 @@ static size_t ZSTDMT_createCompressionJob(ZSTDMT_CCtx* zcs, size_t srcSize, unsi
 static size_t ZSTDMT_flushNextJob(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output, unsigned blockToFlush)
 {
     unsigned const wJobID = zcs->doneJobID & zcs->jobIDMask;
+    DEBUGLOG(5, "ZSTDMT_flushNextJob");
     if (zcs->doneJobID == zcs->nextJobID) return 0;   /* all flushed ! */
     ZSTD_PTHREAD_MUTEX_LOCK(&zcs->jobCompleted_mutex);
     while (zcs->jobs[wJobID].jobCompleted==0) {
@@ -942,7 +986,8 @@ static size_t ZSTDMT_flushNextJob(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output, unsi
     {   ZSTDMT_jobDescription job = zcs->jobs[wJobID];
         if (!job.jobScanned) {
             if (ZSTD_isError(job.cSize)) {
-                DEBUGLOG(5, "compression error detected ");
+                DEBUGLOG(5, "job %u : compression error detected : %s",
+                            zcs->doneJobID, ZSTD_getErrorName(job.cSize));
                 ZSTDMT_waitForAllJobsCompleted(zcs);
                 ZSTDMT_releaseAllJobResources(zcs);
                 return job.cSize;
@@ -991,15 +1036,18 @@ size_t ZSTDMT_compressStream_generic(ZSTDMT_CCtx* mtctx,
 {
     size_t const newJobThreshold = mtctx->dictSize + mtctx->targetSectionSize;
     unsigned forwardInputProgress = 0;
+    DEBUGLOG(5, "ZSTDMT_compressStream_generic ");
     assert(output->pos <= output->size);
     assert(input->pos  <= input->size);
+
+    if (mtctx->singleThreaded) {  /* delegate to single-thread (synchronous) */
+        return ZSTD_compressStream_generic(mtctx->cctxPool->cctx[0], output, input, endOp);
+    }
+
     if ((mtctx->frameEnded) && (endOp==ZSTD_e_continue)) {
         /* current frame being ended. Only flush/end are allowed */
         return ERROR(stage_wrong);
     }
-    if (mtctx->params.nbThreads==1) {  /* delegate to single-thread (synchronous) */
-        return ZSTD_compressStream_generic(mtctx->cctxPool->cctx[0], output, input, endOp);
-    }
 
     /* single-pass shortcut (note : synchronous-mode) */
     if ( (mtctx->nextJobID == 0)     /* just started */
@@ -1068,32 +1116,34 @@ size_t ZSTDMT_compressStream(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output, ZSTD_inBu
 }
 
 
-static size_t ZSTDMT_flushStream_internal(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output, unsigned endFrame)
+static size_t ZSTDMT_flushStream_internal(ZSTDMT_CCtx* mtctx, ZSTD_outBuffer* output, unsigned endFrame)
 {
-    size_t const srcSize = zcs->inBuff.filled - zcs->dictSize;
+    size_t const srcSize = mtctx->inBuff.filled - mtctx->dictSize;
+    DEBUGLOG(5, "ZSTDMT_flushStream_internal");
 
-    if ( ((srcSize > 0) || (endFrame && !zcs->frameEnded))
-       && (zcs->nextJobID <= zcs->doneJobID + zcs->jobIDMask) ) {
-        CHECK_F( ZSTDMT_createCompressionJob(zcs, srcSize, endFrame) );
+    if ( ((srcSize > 0) || (endFrame && !mtctx->frameEnded))
+       && (mtctx->nextJobID <= mtctx->doneJobID + mtctx->jobIDMask) ) {
+           DEBUGLOG(5, "ZSTDMT_flushStream_internal : create a new job");
+        CHECK_F( ZSTDMT_createCompressionJob(mtctx, srcSize, endFrame) );
     }
 
     /* check if there is any data available to flush */
-    return ZSTDMT_flushNextJob(zcs, output, 1 /* blockToFlush */);
+    return ZSTDMT_flushNextJob(mtctx, output, 1 /* blockToFlush */);
 }
 
 
-size_t ZSTDMT_flushStream(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output)
+size_t ZSTDMT_flushStream(ZSTDMT_CCtx* mtctx, ZSTD_outBuffer* output)
 {
     DEBUGLOG(5, "ZSTDMT_flushStream");
-    if (zcs->params.nbThreads==1)
-        return ZSTD_flushStream(zcs->cctxPool->cctx[0], output);
-    return ZSTDMT_flushStream_internal(zcs, output, 0 /* endFrame */);
+    if (mtctx->singleThreaded)
+        return ZSTD_flushStream(mtctx->cctxPool->cctx[0], output);
+    return ZSTDMT_flushStream_internal(mtctx, output, 0 /* endFrame */);
 }
 
-size_t ZSTDMT_endStream(ZSTDMT_CCtx* zcs, ZSTD_outBuffer* output)
+size_t ZSTDMT_endStream(ZSTDMT_CCtx* mtctx, ZSTD_outBuffer* output)
 {
     DEBUGLOG(4, "ZSTDMT_endStream");
-    if (zcs->params.nbThreads==1)
-        return ZSTD_endStream(zcs->cctxPool->cctx[0], output);
-    return ZSTDMT_flushStream_internal(zcs, output, 1 /* endFrame */);
+    if (mtctx->singleThreaded)
+        return ZSTD_endStream(mtctx->cctxPool->cctx[0], output);
+    return ZSTDMT_flushStream_internal(mtctx, output, 1 /* endFrame */);
 }
diff --git a/thirdparty/zstd/compress/zstdmt_compress.h b/thirdparty/zstd/compress/zstdmt_compress.h
index 8c59c684f1..d12f0adb8d 100644
--- a/thirdparty/zstd/compress/zstdmt_compress.h
+++ b/thirdparty/zstd/compress/zstdmt_compress.h
@@ -50,7 +50,7 @@ ZSTDLIB_API size_t ZSTDMT_compressCCtx(ZSTDMT_CCtx* mtctx,
 /* ===   Streaming functions   === */
 
 ZSTDLIB_API size_t ZSTDMT_initCStream(ZSTDMT_CCtx* mtctx, int compressionLevel);
-ZSTDLIB_API size_t ZSTDMT_resetCStream(ZSTDMT_CCtx* mtctx, unsigned long long pledgedSrcSize);    /**< pledgedSrcSize is optional and can be zero == unknown */
+ZSTDLIB_API size_t ZSTDMT_resetCStream(ZSTDMT_CCtx* mtctx, unsigned long long pledgedSrcSize);  /**< if srcSize is not known at reset time, use ZSTD_CONTENTSIZE_UNKNOWN. Note: for compatibility with older programs, 0 means the same as ZSTD_CONTENTSIZE_UNKNOWN, but it may change in the future, to mean "empty" */
 
 ZSTDLIB_API size_t ZSTDMT_compressStream(ZSTDMT_CCtx* mtctx, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
 
@@ -60,8 +60,8 @@ ZSTDLIB_API size_t ZSTDMT_endStream(ZSTDMT_CCtx* mtctx, ZSTD_outBuffer* output);
 
 /* ===   Advanced functions and parameters  === */
 
-#ifndef ZSTDMT_SECTION_SIZE_MIN
-#  define ZSTDMT_SECTION_SIZE_MIN (1U << 20)   /* 1 MB - Minimum size of each compression job */
+#ifndef ZSTDMT_JOBSIZE_MIN
+#  define ZSTDMT_JOBSIZE_MIN (1U << 20)   /* 1 MB - Minimum size of each compression job */
 #endif
 
 ZSTDLIB_API size_t ZSTDMT_compress_advanced(ZSTDMT_CCtx* mtctx,
@@ -84,13 +84,13 @@ ZSTDLIB_API size_t ZSTDMT_initCStream_usingCDict(ZSTDMT_CCtx* mtctx,
 /* ZSTDMT_parameter :
  * List of parameters that can be set using ZSTDMT_setMTCtxParameter() */
 typedef enum {
-    ZSTDMT_p_sectionSize,        /* size of input "section". Each section is compressed in parallel. 0 means default, which is dynamically determined within compression functions */
-    ZSTDMT_p_overlapSectionLog   /* Log of overlapped section; 0 == no overlap, 6(default) == use 1/8th of window, >=9 == use full window */
+    ZSTDMT_p_jobSize,           /* Each job is compressed in parallel. By default, this value is dynamically determined depending on compression parameters. Can be set explicitly here. */
+    ZSTDMT_p_overlapSectionLog  /* Each job may reload a part of previous job to enhance compressionr ratio; 0 == no overlap, 6(default) == use 1/8th of window, >=9 == use full window */
 } ZSTDMT_parameter;
 
 /* ZSTDMT_setMTCtxParameter() :
  * allow setting individual parameters, one at a time, among a list of enums defined in ZSTDMT_parameter.
- * The function must be called typically after ZSTD_createCCtx().
+ * The function must be called typically after ZSTD_createCCtx() but __before ZSTDMT_init*() !__
  * Parameters not explicitly reset by ZSTDMT_init*() remain the same in consecutive compression sessions.
  * @return : 0, or an error code (which can be tested using ZSTD_isError()) */
 ZSTDLIB_API size_t ZSTDMT_setMTCtxParameter(ZSTDMT_CCtx* mtctx, ZSTDMT_parameter parameter, unsigned value);
@@ -112,7 +112,15 @@ ZSTDLIB_API size_t ZSTDMT_compressStream_generic(ZSTDMT_CCtx* mtctx,
 
 size_t ZSTDMT_CCtxParam_setMTCtxParameter(ZSTD_CCtx_params* params, ZSTDMT_parameter parameter, unsigned value);
 
-size_t ZSTDMT_initializeCCtxParameters(ZSTD_CCtx_params* params, unsigned nbThreads);
+/* ZSTDMT_CCtxParam_setNbThreads()
+ * Set nbThreads, and clamp it correctly,
+ * also reset jobSize and overlapLog */
+size_t ZSTDMT_CCtxParam_setNbThreads(ZSTD_CCtx_params* params, unsigned nbThreads);
+
+/* ZSTDMT_getNbThreads():
+ * @return nb threads currently active in mtctx.
+ * mtctx must be valid */
+size_t ZSTDMT_getNbThreads(const ZSTDMT_CCtx* mtctx);
 
 /*! ZSTDMT_initCStream_internal() :
  *  Private use only. Init streaming operation.
diff --git a/thirdparty/zstd/decompress/zstd_decompress.c b/thirdparty/zstd/decompress/zstd_decompress.c
index 96fc609089..a59d944112 100644
--- a/thirdparty/zstd/decompress/zstd_decompress.c
+++ b/thirdparty/zstd/decompress/zstd_decompress.c
@@ -827,9 +827,9 @@ typedef struct {
     FSE_DState_t stateOffb;
     FSE_DState_t stateML;
     size_t prevOffset[ZSTD_REP_NUM];
-    const BYTE* base;
+    const BYTE* prefixStart;
+    const BYTE* dictEnd;
     size_t pos;
-    uPtrDiff gotoDict;
 } seqState_t;
 
 
@@ -1224,8 +1224,9 @@ seq_t ZSTD_decodeSequenceLong(seqState_t* seqState, ZSTD_longOffset_e const long
         BIT_reloadDStream(&seqState->DStream);
 
     {   size_t const pos = seqState->pos + seq.litLength;
-        seq.match = seqState->base + pos - seq.offset;    /* single memory segment */
-        if (seq.offset > pos) seq.match += seqState->gotoDict;   /* separate memory segment */
+        const BYTE* const matchBase = (seq.offset > pos) ? seqState->dictEnd : seqState->prefixStart;
+        seq.match = matchBase + pos - seq.offset;  /* note : this operation can overflow when seq.offset is really too large, which can only happen when input is corrupted.
+                                                    * No consequence though : no memory access will occur, overly large offset will be detected in ZSTD_execSequenceLong() */
         seqState->pos = pos + seq.matchLength;
     }
 
@@ -1243,7 +1244,7 @@ HINT_INLINE
 size_t ZSTD_execSequenceLong(BYTE* op,
                              BYTE* const oend, seq_t sequence,
                              const BYTE** litPtr, const BYTE* const litLimit,
-                             const BYTE* const base, const BYTE* const vBase, const BYTE* const dictEnd)
+                             const BYTE* const prefixStart, const BYTE* const dictStart, const BYTE* const dictEnd)
 {
     BYTE* const oLitEnd = op + sequence.litLength;
     size_t const sequenceLength = sequence.litLength + sequence.matchLength;
@@ -1253,21 +1254,21 @@ size_t ZSTD_execSequenceLong(BYTE* op,
     const BYTE* match = sequence.match;
 
     /* check */
-    if (oMatchEnd>oend) return ERROR(dstSize_tooSmall); /* last match must start at a minimum distance of WILDCOPY_OVERLENGTH from oend */
+    if (oMatchEnd > oend) return ERROR(dstSize_tooSmall); /* last match must start at a minimum distance of WILDCOPY_OVERLENGTH from oend */
     if (iLitEnd > litLimit) return ERROR(corruption_detected);   /* over-read beyond lit buffer */
-    if (oLitEnd>oend_w) return ZSTD_execSequenceLast7(op, oend, sequence, litPtr, litLimit, base, vBase, dictEnd);
+    if (oLitEnd > oend_w) return ZSTD_execSequenceLast7(op, oend, sequence, litPtr, litLimit, prefixStart, dictStart, dictEnd);
 
     /* copy Literals */
-    ZSTD_copy8(op, *litPtr);
+    ZSTD_copy8(op, *litPtr);  /* note : op <= oLitEnd <= oend_w == oend - 8 */
     if (sequence.litLength > 8)
         ZSTD_wildcopy(op+8, (*litPtr)+8, sequence.litLength - 8);   /* note : since oLitEnd <= oend-WILDCOPY_OVERLENGTH, no risk of overwrite beyond oend */
     op = oLitEnd;
     *litPtr = iLitEnd;   /* update for next sequence */
 
     /* copy Match */
-    if (sequence.offset > (size_t)(oLitEnd - base)) {
+    if (sequence.offset > (size_t)(oLitEnd - prefixStart)) {
         /* offset beyond prefix */
-        if (sequence.offset > (size_t)(oLitEnd - vBase)) return ERROR(corruption_detected);
+        if (sequence.offset > (size_t)(oLitEnd - dictStart)) return ERROR(corruption_detected);
         if (match + sequence.matchLength <= dictEnd) {
             memmove(oLitEnd, match, sequence.matchLength);
             return sequenceLength;
@@ -1277,7 +1278,7 @@ size_t ZSTD_execSequenceLong(BYTE* op,
             memmove(oLitEnd, match, length1);
             op = oLitEnd + length1;
             sequence.matchLength -= length1;
-            match = base;
+            match = prefixStart;
             if (op > oend_w || sequence.matchLength < MINMATCH) {
               U32 i;
               for (i = 0; i < sequence.matchLength; ++i) op[i] = match[i];
@@ -1331,8 +1332,8 @@ static size_t ZSTD_decompressSequencesLong(
     BYTE* op = ostart;
     const BYTE* litPtr = dctx->litPtr;
     const BYTE* const litEnd = litPtr + dctx->litSize;
-    const BYTE* const base = (const BYTE*) (dctx->base);
-    const BYTE* const vBase = (const BYTE*) (dctx->vBase);
+    const BYTE* const prefixStart = (const BYTE*) (dctx->base);
+    const BYTE* const dictStart = (const BYTE*) (dctx->vBase);
     const BYTE* const dictEnd = (const BYTE*) (dctx->dictEnd);
     int nbSeq;
 
@@ -1353,9 +1354,9 @@ static size_t ZSTD_decompressSequencesLong(
         int seqNb;
         dctx->fseEntropy = 1;
         { U32 i; for (i=0; i<ZSTD_REP_NUM; i++) seqState.prevOffset[i] = dctx->entropy.rep[i]; }
-        seqState.base = base;
-        seqState.pos = (size_t)(op-base);
-        seqState.gotoDict = (uPtrDiff)dictEnd - (uPtrDiff)base; /* cast to avoid undefined behaviour */
+        seqState.prefixStart = prefixStart;
+        seqState.pos = (size_t)(op-prefixStart);
+        seqState.dictEnd = dictEnd;
         CHECK_E(BIT_initDStream(&seqState.DStream, ip, iend-ip), corruption_detected);
         FSE_initDState(&seqState.stateLL, &seqState.DStream, dctx->LLTptr);
         FSE_initDState(&seqState.stateOffb, &seqState.DStream, dctx->OFTptr);
@@ -1370,9 +1371,9 @@ static size_t ZSTD_decompressSequencesLong(
         /* decode and decompress */
         for ( ; (BIT_reloadDStream(&(seqState.DStream)) <= BIT_DStream_completed) && seqNb<nbSeq ; seqNb++) {
             seq_t const sequence = ZSTD_decodeSequenceLong(&seqState, isLongOffset);
-            size_t const oneSeqSize = ZSTD_execSequenceLong(op, oend, sequences[(seqNb-ADVANCED_SEQS) & STOSEQ_MASK], &litPtr, litEnd, base, vBase, dictEnd);
+            size_t const oneSeqSize = ZSTD_execSequenceLong(op, oend, sequences[(seqNb-ADVANCED_SEQS) & STOSEQ_MASK], &litPtr, litEnd, prefixStart, dictStart, dictEnd);
             if (ZSTD_isError(oneSeqSize)) return oneSeqSize;
-            PREFETCH(sequence.match);
+            PREFETCH(sequence.match);  /* note : it's safe to invoke PREFETCH() on any memory address, including invalid ones */
             sequences[seqNb&STOSEQ_MASK] = sequence;
             op += oneSeqSize;
         }
@@ -1381,7 +1382,7 @@ static size_t ZSTD_decompressSequencesLong(
         /* finish queue */
         seqNb -= seqAdvance;
         for ( ; seqNb<nbSeq ; seqNb++) {
-            size_t const oneSeqSize = ZSTD_execSequenceLong(op, oend, sequences[seqNb&STOSEQ_MASK], &litPtr, litEnd, base, vBase, dictEnd);
+            size_t const oneSeqSize = ZSTD_execSequenceLong(op, oend, sequences[seqNb&STOSEQ_MASK], &litPtr, litEnd, prefixStart, dictStart, dictEnd);
             if (ZSTD_isError(oneSeqSize)) return oneSeqSize;
             op += oneSeqSize;
         }
@@ -2450,14 +2451,16 @@ size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inB
                         return ZSTD_decompressLegacyStream(zds->legacyContext, legacyVersion, output, input);
                     }
 #endif
-                    return hSize; /* error */
+                    return hSize;   /* error */
                 }
                 if (hSize != 0) {   /* need more input */
                     size_t const toLoad = hSize - zds->lhSize;   /* if hSize!=0, hSize > zds->lhSize */
-                    if (toLoad > (size_t)(iend-ip)) {   /* not enough input to load full header */
-                        if (iend-ip > 0) {
-                            memcpy(zds->headerBuffer + zds->lhSize, ip, iend-ip);
-                            zds->lhSize += iend-ip;
+                    size_t const remainingInput = (size_t)(iend-ip);
+                    assert(iend >= ip);
+                    if (toLoad > remainingInput) {   /* not enough input to load full header */
+                        if (remainingInput > 0) {
+                            memcpy(zds->headerBuffer + zds->lhSize, ip, remainingInput);
+                            zds->lhSize += remainingInput;
                         }
                         input->pos = input->size;
                         return (MAX(ZSTD_frameHeaderSize_min, hSize) - zds->lhSize) + ZSTD_blockHeaderSize;   /* remaining header bytes + next block header */
@@ -2472,8 +2475,10 @@ size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inB
                 && (U64)(size_t)(oend-op) >= zds->fParams.frameContentSize) {
                 size_t const cSize = ZSTD_findFrameCompressedSize(istart, iend-istart);
                 if (cSize <= (size_t)(iend-istart)) {
+                    /* shortcut : using single-pass mode */
                     size_t const decompressedSize = ZSTD_decompress_usingDDict(zds, op, oend-op, istart, cSize, zds->ddict);
                     if (ZSTD_isError(decompressedSize)) return decompressedSize;
+                    DEBUGLOG(4, "shortcut to single-pass ZSTD_decompress_usingDDict()")
                     ip = istart + cSize;
                     op += decompressedSize;
                     zds->expected = 0;
@@ -2496,8 +2501,9 @@ size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inB
             }
 
             /* control buffer memory usage */
-            DEBUGLOG(4, "Control max buffer memory usage (max %u KB)",
-                        (U32)(zds->maxWindowSize >> 10));
+            DEBUGLOG(4, "Control max memory usage (%u KB <= max %u KB)",
+                        (U32)(zds->fParams.windowSize >>10),
+                        (U32)(zds->maxWindowSize >> 10) );
             zds->fParams.windowSize = MAX(zds->fParams.windowSize, 1U << ZSTD_WINDOWLOG_ABSOLUTEMIN);
             if (zds->fParams.windowSize > zds->maxWindowSize) return ERROR(frameParameter_windowTooLarge);
 
@@ -2555,17 +2561,21 @@ size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inB
             /* fall-through */
         case zdss_load:
             {   size_t const neededInSize = ZSTD_nextSrcSizeToDecompress(zds);
-                size_t const toLoad = neededInSize - zds->inPos;   /* should always be <= remaining space within inBuff */
+                size_t const toLoad = neededInSize - zds->inPos;
+                int const isSkipFrame = ZSTD_isSkipFrame(zds);
                 size_t loadedSize;
-                if (toLoad > zds->inBuffSize - zds->inPos) return ERROR(corruption_detected);   /* should never happen */
-                loadedSize = ZSTD_limitCopy(zds->inBuff + zds->inPos, toLoad, ip, iend-ip);
+                if (isSkipFrame) {
+                    loadedSize = MIN(toLoad, (size_t)(iend-ip));
+                } else {
+                    if (toLoad > zds->inBuffSize - zds->inPos) return ERROR(corruption_detected);   /* should never happen */
+                    loadedSize = ZSTD_limitCopy(zds->inBuff + zds->inPos, toLoad, ip, iend-ip);
+                }
                 ip += loadedSize;
                 zds->inPos += loadedSize;
                 if (loadedSize < toLoad) { someMoreWork = 0; break; }   /* not enough input, wait for more */
 
                 /* decode loaded input */
-                {  const int isSkipFrame = ZSTD_isSkipFrame(zds);
-                   size_t const decodedSize = ZSTD_decompressContinue(zds,
+                {   size_t const decodedSize = ZSTD_decompressContinue(zds,
                         zds->outBuff + zds->outStart, zds->outBuffSize - zds->outStart,
                         zds->inBuff, neededInSize);
                     if (ZSTD_isError(decodedSize)) return decodedSize;
diff --git a/thirdparty/zstd/zstd.h b/thirdparty/zstd/zstd.h
index 2194a3b23d..9ac0a73dce 100644
--- a/thirdparty/zstd/zstd.h
+++ b/thirdparty/zstd/zstd.h
@@ -59,7 +59,7 @@ extern "C" {
 /*------   Version   ------*/
 #define ZSTD_VERSION_MAJOR    1
 #define ZSTD_VERSION_MINOR    3
-#define ZSTD_VERSION_RELEASE  2
+#define ZSTD_VERSION_RELEASE  3
 
 #define ZSTD_VERSION_NUMBER  (ZSTD_VERSION_MAJOR *100*100 + ZSTD_VERSION_MINOR *100 + ZSTD_VERSION_RELEASE)
 ZSTDLIB_API unsigned ZSTD_versionNumber(void);   /**< useful to check dll version */
@@ -131,7 +131,7 @@ ZSTDLIB_API unsigned long long ZSTD_getDecompressedSize(const void* src, size_t
 
 
 /*======  Helper functions  ======*/
-#define ZSTD_COMPRESSBOUND(srcSize)   ((srcSize) + ((srcSize)>>8) + (((srcSize) < 128 KB) ? ((128 KB - (srcSize)) >> 11) /* margin, from 64 to 0 */ : 0))  /* this formula ensures that bound(A) + bound(B) <= bound(A+B) as long as A and B >= 128 KB */
+#define ZSTD_COMPRESSBOUND(srcSize)   ((srcSize) + ((srcSize)>>8) + (((srcSize) < (128<<10)) ? (((128<<10) - (srcSize)) >> 11) /* margin, from 64 to 0 */ : 0))  /* this formula ensures that bound(A) + bound(B) <= bound(A+B) as long as A and B >= 128 KB */
 ZSTDLIB_API size_t      ZSTD_compressBound(size_t srcSize); /*!< maximum compressed size in worst case scenario */
 ZSTDLIB_API unsigned    ZSTD_isError(size_t code);          /*!< tells if a `size_t` function result is an error code */
 ZSTDLIB_API const char* ZSTD_getErrorName(size_t code);     /*!< provides readable string from an error code */
@@ -432,12 +432,12 @@ typedef struct {
 
 typedef struct ZSTD_CCtx_params_s ZSTD_CCtx_params;
 
-/*= Custom memory allocation functions */
+/*--- Custom memory allocation functions ---*/
 typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
 typedef void  (*ZSTD_freeFunction) (void* opaque, void* address);
 typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
 /* use this constant to defer to stdlib's functions */
-static const ZSTD_customMem ZSTD_defaultCMem = { NULL, NULL, NULL };
+static ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL };
 
 
 /***************************************
@@ -446,7 +446,7 @@ static const ZSTD_customMem ZSTD_defaultCMem = { NULL, NULL, NULL };
 
 /*! ZSTD_findFrameCompressedSize() :
  *  `src` should point to the start of a ZSTD encoded frame or skippable frame
- *  `srcSize` must be at least as large as the frame
+ *  `srcSize` must be >= first frame size
  *  @return : the compressed size of the first frame starting at `src`,
  *            suitable to pass to `ZSTD_decompress` or similar,
  *            or an error code if input is invalid */
@@ -557,7 +557,8 @@ ZSTDLIB_API ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
  *             It must outlive context usage.
  *  workspaceSize: Use ZSTD_estimateCCtxSize() or ZSTD_estimateCStreamSize()
  *                 to determine how large workspace must be to support scenario.
- * @return : pointer to ZSTD_CCtx*, or NULL if error (size too small)
+ * @return : pointer to ZSTD_CCtx* (same address as workspace, but different type),
+ *           or NULL if error (typically size too small)
  *  Note : zstd will never resize nor malloc() when using a static cctx.
  *         If it needs more memory than available, it will simply error out.
  *  Note 2 : there is no corresponding "free" function.
@@ -587,7 +588,7 @@ ZSTDLIB_API ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictS
                                                   ZSTD_compressionParameters cParams,
                                                   ZSTD_customMem customMem);
 
-/*! ZSTD_initStaticCDict_advanced() :
+/*! ZSTD_initStaticCDict() :
  *  Generate a digested dictionary in provided memory area.
  *  workspace: The memory area to emplace the dictionary into.
  *             Provided pointer must 8-bytes aligned.
@@ -596,7 +597,8 @@ ZSTDLIB_API ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictS
  *                 to determine how large workspace must be.
  *  cParams : use ZSTD_getCParams() to transform a compression level
  *            into its relevants cParams.
- * @return : pointer to ZSTD_CDict*, or NULL if error (size too small)
+ * @return : pointer to ZSTD_CDict* (same address as workspace, but different type),
+ *           or NULL if error (typically, size too small).
  *  Note : there is no corresponding "free" function.
  *         Since workspace was allocated externally, it must be freed externally.
  */
@@ -613,7 +615,7 @@ ZSTDLIB_API ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, uns
 
 /*! ZSTD_getParams() :
 *   same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`.
-*   All fields of `ZSTD_frameParameters` are set to default (0) */
+*   All fields of `ZSTD_frameParameters` are set to default : contentSize=1, checksum=0, noDictID=0 */
 ZSTDLIB_API ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
 
 /*! ZSTD_checkCParams() :
@@ -660,7 +662,8 @@ ZSTDLIB_API ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
  *             It must outlive context usage.
  *  workspaceSize: Use ZSTD_estimateDCtxSize() or ZSTD_estimateDStreamSize()
  *                 to determine how large workspace must be to support scenario.
- * @return : pointer to ZSTD_DCtx*, or NULL if error (size too small)
+ * @return : pointer to ZSTD_DCtx* (same address as workspace, but different type),
+ *           or NULL if error (typically size too small)
  *  Note : zstd will never resize nor malloc() when using a static dctx.
  *         If it needs more memory than available, it will simply error out.
  *  Note 2 : static dctx is incompatible with legacy support
@@ -731,20 +734,22 @@ ZSTDLIB_API unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
 /*=====   Advanced Streaming compression functions  =====*/
 ZSTDLIB_API ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
 ZSTDLIB_API ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize);    /**< same as ZSTD_initStaticCCtx() */
-ZSTDLIB_API size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize);   /**< pledgedSrcSize must be correct, a size of 0 means unknown.  for a frame size of 0 use initCStream_advanced */
+ZSTDLIB_API size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize);   /**< pledgedSrcSize must be correct. If it is not known at init time, use ZSTD_CONTENTSIZE_UNKNOWN. Note that, for compatibility with older programs, "0" also disables frame content size field. It may be enabled in the future. */
 ZSTDLIB_API size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); /**< creates of an internal CDict (incompatible with static CCtx), except if dict == NULL or dictSize < 8, in which case no dict is used. Note: dict is loaded with ZSTD_dm_auto (treated as a full zstd dictionary if it begins with ZSTD_MAGIC_DICTIONARY, else as raw content) and ZSTD_dlm_byCopy.*/
 ZSTDLIB_API size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
-                                             ZSTD_parameters params, unsigned long long pledgedSrcSize);  /**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0. dict is loaded with ZSTD_dm_auto and ZSTD_dlm_byCopy. */
+                                             ZSTD_parameters params, unsigned long long pledgedSrcSize);  /**< pledgedSrcSize must be correct. If srcSize is not known at init time, use value ZSTD_CONTENTSIZE_UNKNOWN. dict is loaded with ZSTD_dm_auto and ZSTD_dlm_byCopy. */
 ZSTDLIB_API size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict);  /**< note : cdict will just be referenced, and must outlive compression session */
-ZSTDLIB_API size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, ZSTD_frameParameters fParams, unsigned long long pledgedSrcSize);  /**< same as ZSTD_initCStream_usingCDict(), with control over frame parameters */
+ZSTDLIB_API size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, ZSTD_frameParameters fParams, unsigned long long pledgedSrcSize);  /**< same as ZSTD_initCStream_usingCDict(), with control over frame parameters. pledgedSrcSize must be correct. If srcSize is not known at init time, use value ZSTD_CONTENTSIZE_UNKNOWN. */
 
 /*! ZSTD_resetCStream() :
  *  start a new compression job, using same parameters from previous job.
  *  This is typically useful to skip dictionary loading stage, since it will re-use it in-place..
  *  Note that zcs must be init at least once before using ZSTD_resetCStream().
- *  pledgedSrcSize==0 means "srcSize unknown".
+ *  If pledgedSrcSize is not known at reset time, use macro ZSTD_CONTENTSIZE_UNKNOWN.
  *  If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end.
- *  @return : 0, or an error code (which can be tested using ZSTD_isError()) */
+ *  For the time being, pledgedSrcSize==0 is interpreted as "srcSize unknown" for compatibility with older programs,
+ *  but it may change to mean "empty" in some future version, so prefer using macro ZSTD_CONTENTSIZE_UNKNOWN.
+ * @return : 0, or an error code (which can be tested using ZSTD_isError()) */
 ZSTDLIB_API size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize);
 
 
@@ -800,10 +805,10 @@ ZSTDLIB_API size_t ZSTD_resetDStream(ZSTD_DStream* zds);  /**< re-use decompress
 /*=====   Buffer-less streaming compression functions  =====*/
 ZSTDLIB_API size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
 ZSTDLIB_API size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
-ZSTDLIB_API size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize); /**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */
+ZSTDLIB_API size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize); /**< pledgedSrcSize : If srcSize is not known at init time, use ZSTD_CONTENTSIZE_UNKNOWN */
 ZSTDLIB_API size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); /**< note: fails if cdict==NULL */
-ZSTDLIB_API size_t ZSTD_compressBegin_usingCDict_advanced(ZSTD_CCtx* const cctx, const ZSTD_CDict* const cdict, ZSTD_frameParameters const fParams, unsigned long long const pledgedSrcSize);   /* compression parameters are already set within cdict. pledgedSrcSize=0 means null-size */
-ZSTDLIB_API size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize); /**<  note: if pledgedSrcSize can be 0, indicating unknown size.  if it is non-zero, it must be accurate.  for 0 size frames, use compressBegin_advanced */
+ZSTDLIB_API size_t ZSTD_compressBegin_usingCDict_advanced(ZSTD_CCtx* const cctx, const ZSTD_CDict* const cdict, ZSTD_frameParameters const fParams, unsigned long long const pledgedSrcSize);   /* compression parameters are already set within cdict. pledgedSrcSize must be correct. If srcSize is not known, use macro ZSTD_CONTENTSIZE_UNKNOWN */
+ZSTDLIB_API size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize); /**<  note: if pledgedSrcSize is not known, use ZSTD_CONTENTSIZE_UNKNOWN */
 
 ZSTDLIB_API size_t ZSTD_compressContinue(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
 ZSTDLIB_API size_t ZSTD_compressEnd(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
@@ -1000,18 +1005,19 @@ typedef enum {
                               * Special: value 0 means "do not change strategy". */
 
     /* frame parameters */
-    ZSTD_p_contentSizeFlag=200, /* Content size is written into frame header _whenever known_ (default:1)
-                              * note that content size must be known at the beginning,
-                              * it is sent using ZSTD_CCtx_setPledgedSrcSize() */
+    ZSTD_p_contentSizeFlag=200, /* Content size will be written into frame header _whenever known_ (default:1)
+                              * Content size must be known at the beginning of compression,
+                              * it is provided using ZSTD_CCtx_setPledgedSrcSize() */
     ZSTD_p_checksumFlag,     /* A 32-bits checksum of content is written at end of frame (default:0) */
-    ZSTD_p_dictIDFlag,       /* When applicable, dictID of dictionary is provided in frame header (default:1) */
+    ZSTD_p_dictIDFlag,       /* When applicable, dictionary's ID is written into frame header (default:1) */
 
     /* multi-threading parameters */
     ZSTD_p_nbThreads=400,    /* Select how many threads a compression job can spawn (default:1)
                               * More threads improve speed, but also increase memory usage.
                               * Can only receive a value > 1 if ZSTD_MULTITHREAD is enabled.
                               * Special: value 0 means "do not change nbThreads" */
-    ZSTD_p_jobSize,          /* Size of a compression job. Each compression job is completed in parallel.
+    ZSTD_p_jobSize,          /* Size of a compression job. This value is only enforced in streaming (non-blocking) mode.
+                              * Each compression job is completed in parallel, so indirectly controls the nb of active threads.
                               * 0 means default, which is dynamically determined based on compression parameters.
                               * Job size must be a minimum of overlapSize, or 1 KB, whichever is largest
                               * The minimum size is automatically and transparently enforced */
@@ -1057,7 +1063,8 @@ typedef enum {
 /*! ZSTD_CCtx_setParameter() :
  *  Set one compression parameter, selected by enum ZSTD_cParameter.
  *  Note : when `value` is an enum, cast it to unsigned for proper type checking.
- *  @result : 0, or an error code (which can be tested with ZSTD_isError()). */
+ *  @result : informational value (typically, the one being set, possibly corrected),
+ *            or an error code (which can be tested with ZSTD_isError()). */
 ZSTDLIB_API size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned value);
 
 /*! ZSTD_CCtx_setPledgedSrcSize() :
@@ -1066,7 +1073,7 @@ ZSTDLIB_API size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param
  * @result : 0, or an error code (which can be tested with ZSTD_isError()).
  *  Note 1 : 0 means zero, empty.
  *           In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN.
- *           Note that ZSTD_CONTENTSIZE_UNKNOWN is default value for new compression jobs.
+ *           ZSTD_CONTENTSIZE_UNKNOWN is default value for any new compression job.
  *  Note 2 : If all data is provided and consumed in a single round,
  *           this value is overriden by srcSize instead. */
 ZSTDLIB_API size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize);
@@ -1138,13 +1145,19 @@ typedef enum {
  *  - Compression parameters cannot be changed once compression is started.
  *  - outpot->pos must be <= dstCapacity, input->pos must be <= srcSize
  *  - outpot->pos and input->pos will be updated. They are guaranteed to remain below their respective limit.
- *  - @return provides the minimum amount of data still to flush from internal buffers
+ *  - In single-thread mode (default), function is blocking : it completed its job before returning to caller.
+ *  - In multi-thread mode, function is non-blocking : it just acquires a copy of input, and distribute job to internal worker threads,
+ *                                                     and then immediately returns, just indicating that there is some data remaining to be flushed.
+ *                                                     The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte.
+ *  - Exception : in multi-threading mode, if the first call requests a ZSTD_e_end directive, it is blocking : it will complete compression before giving back control to caller.
+ *  - @return provides the minimum amount of data remaining to be flushed from internal buffers
  *            or an error code, which can be tested using ZSTD_isError().
- *            if @return != 0, flush is not fully completed, there is some data left within internal buffers.
- *  - after a ZSTD_e_end directive, if internal buffer is not fully flushed,
+ *            if @return != 0, flush is not fully completed, there is still some data left within internal buffers.
+ *            This is useful to determine if a ZSTD_e_flush or ZSTD_e_end directive is completed.
+ *  - after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0),
  *            only ZSTD_e_end or ZSTD_e_flush operations are allowed.
- *            It is necessary to fully flush internal buffers
- *            before starting a new compression job, or changing compression parameters.
+ *            Before starting a new compression job, or changing compression parameters,
+ *            it is required to fully flush internal buffers.
  */
 ZSTDLIB_API size_t ZSTD_compress_generic (ZSTD_CCtx* cctx,
                                           ZSTD_outBuffer* output,