Drop obsolete "webpold" backup of previous webp version

Fixes #5252

1 files changed, 0 insertions, 874 deletions

diff --git a/drivers/webpold/enc/backward_references.c b/drivers/webpold/enc/backward_references.c
deleted file mode 100644
index b8c8ece806..0000000000
--- a/drivers/webpold/enc/backward_references.c
+++ /dev/null
@@ -1,874 +0,0 @@
-// Copyright 2012 Google Inc. All Rights Reserved.
-//
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
-// -----------------------------------------------------------------------------
-//
-// Author: Jyrki Alakuijala (jyrki@google.com)
-//
-
-#include <assert.h>
-#include <math.h>
-#include <stdio.h>
-
-#include "./backward_references.h"
-#include "./histogram.h"
-#include "../dsp/lossless.h"
-#include "../utils/color_cache.h"
-#include "../utils/utils.h"
-
-#define VALUES_IN_BYTE 256
-
-#define HASH_BITS 18
-#define HASH_SIZE (1 << HASH_BITS)
-#define HASH_MULTIPLIER (0xc6a4a7935bd1e995ULL)
-
-// 1M window (4M bytes) minus 120 special codes for short distances.
-#define WINDOW_SIZE ((1 << 20) - 120)
-
-// Bounds for the match length.
-#define MIN_LENGTH 2
-#define MAX_LENGTH 4096
-
-typedef struct {
-  // Stores the most recently added position with the given hash value.
-  int32_t hash_to_first_index_[HASH_SIZE];
-  // chain_[pos] stores the previous position with the same hash value
-  // for every pixel in the image.
-  int32_t* chain_;
-} HashChain;
-
-// -----------------------------------------------------------------------------
-
-static const uint8_t plane_to_code_lut[128] = {
- 96,   73,  55,  39,  23,  13,   5,  1,  255, 255, 255, 255, 255, 255, 255, 255,
- 101,  78,  58,  42,  26,  16,   8,  2,    0,   3,  9,   17,  27,  43,  59,  79,
- 102,  86,  62,  46,  32,  20,  10,  6,    4,   7,  11,  21,  33,  47,  63,  87,
- 105,  90,  70,  52,  37,  28,  18,  14,  12,  15,  19,  29,  38,  53,  71,  91,
- 110,  99,  82,  66,  48,  35,  30,  24,  22,  25,  31,  36,  49,  67,  83, 100,
- 115, 108,  94,  76,  64,  50,  44,  40,  34,  41,  45,  51,  65,  77,  95, 109,
- 118, 113, 103,  92,  80,  68,  60,  56,  54,  57,  61,  69,  81,  93, 104, 114,
- 119, 116, 111, 106,  97,  88,  84,  74,  72,  75,  85,  89,  98, 107, 112, 117
-};
-
-static int DistanceToPlaneCode(int xsize, int dist) {
-  const int yoffset = dist / xsize;
-  const int xoffset = dist - yoffset * xsize;
-  if (xoffset <= 8 && yoffset < 8) {
-    return plane_to_code_lut[yoffset * 16 + 8 - xoffset] + 1;
-  } else if (xoffset > xsize - 8 && yoffset < 7) {
-    return plane_to_code_lut[(yoffset + 1) * 16 + 8 + (xsize - xoffset)] + 1;
-  }
-  return dist + 120;
-}
-
-static WEBP_INLINE int FindMatchLength(const uint32_t* const array1,
-                                       const uint32_t* const array2,
-                                       const int max_limit) {
-  int match_len = 0;
-  while (match_len < max_limit && array1[match_len] == array2[match_len]) {
-    ++match_len;
-  }
-  return match_len;
-}
-
-// -----------------------------------------------------------------------------
-//  VP8LBackwardRefs
-
-void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs) {
-  if (refs != NULL) {
-    refs->refs = NULL;
-    refs->size = 0;
-    refs->max_size = 0;
-  }
-}
-
-void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs) {
-  if (refs != NULL) {
-    free(refs->refs);
-    VP8LInitBackwardRefs(refs);
-  }
-}
-
-int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size) {
-  assert(refs != NULL);
-  refs->size = 0;
-  refs->max_size = 0;
-  refs->refs = (PixOrCopy*)WebPSafeMalloc((uint64_t)max_size,
-                                          sizeof(*refs->refs));
-  if (refs->refs == NULL) return 0;
-  refs->max_size = max_size;
-  return 1;
-}
-
-// -----------------------------------------------------------------------------
-// Hash chains
-
-static WEBP_INLINE uint64_t GetPixPairHash64(const uint32_t* const argb) {
-  uint64_t key = ((uint64_t)(argb[1]) << 32) | argb[0];
-  key = (key * HASH_MULTIPLIER) >> (64 - HASH_BITS);
-  return key;
-}
-
-static int HashChainInit(HashChain* const p, int size) {
-  int i;
-  p->chain_ = (int*)WebPSafeMalloc((uint64_t)size, sizeof(*p->chain_));
-  if (p->chain_ == NULL) {
-    return 0;
-  }
-  for (i = 0; i < size; ++i) {
-    p->chain_[i] = -1;
-  }
-  for (i = 0; i < HASH_SIZE; ++i) {
-    p->hash_to_first_index_[i] = -1;
-  }
-  return 1;
-}
-
-static void HashChainDelete(HashChain* const p) {
-  if (p != NULL) {
-    free(p->chain_);
-    free(p);
-  }
-}
-
-// Insertion of two pixels at a time.
-static void HashChainInsert(HashChain* const p,
-                            const uint32_t* const argb, int pos) {
-  const uint64_t hash_code = GetPixPairHash64(argb);
-  p->chain_[pos] = p->hash_to_first_index_[hash_code];
-  p->hash_to_first_index_[hash_code] = pos;
-}
-
-static int HashChainFindCopy(const HashChain* const p,
-                             int quality, int index, int xsize,
-                             const uint32_t* const argb, int maxlen,
-                             int* const distance_ptr,
-                             int* const length_ptr) {
-  const uint64_t hash_code = GetPixPairHash64(&argb[index]);
-  int prev_length = 0;
-  int64_t best_val = 0;
-  int best_length = 0;
-  int best_distance = 0;
-  const uint32_t* const argb_start = argb + index;
-  const int iter_min_mult = (quality < 50) ? 2 : (quality < 75) ? 4 : 8;
-  const int iter_min = -quality * iter_min_mult;
-  int iter_cnt = 10 + (quality >> 1);
-  const int min_pos = (index > WINDOW_SIZE) ? index - WINDOW_SIZE : 0;
-  int pos;
-
-  assert(xsize > 0);
-  for (pos = p->hash_to_first_index_[hash_code];
-       pos >= min_pos;
-       pos = p->chain_[pos]) {
-    int64_t val;
-    int curr_length;
-    if (iter_cnt < 0) {
-      if (iter_cnt < iter_min || best_val >= 0xff0000) {
-        break;
-      }
-    }
-    --iter_cnt;
-    if (best_length != 0 &&
-        argb[pos + best_length - 1] != argb_start[best_length - 1]) {
-      continue;
-    }
-    curr_length = FindMatchLength(argb + pos, argb_start, maxlen);
-    if (curr_length < prev_length) {
-      continue;
-    }
-    val = 65536 * curr_length;
-    // Favoring 2d locality here gives savings for certain images.
-    if (index - pos < 9 * xsize) {
-      const int y = (index - pos) / xsize;
-      int x = (index - pos) % xsize;
-      if (x > xsize / 2) {
-        x = xsize - x;
-      }
-      if (x <= 7 && x >= -8) {
-        val -= y * y + x * x;
-      } else {
-        val -= 9 * 9 + 9 * 9;
-      }
-    } else {
-      val -= 9 * 9 + 9 * 9;
-    }
-    if (best_val < val) {
-      prev_length = curr_length;
-      best_val = val;
-      best_length = curr_length;
-      best_distance = index - pos;
-      if (curr_length >= MAX_LENGTH) {
-        break;
-      }
-      if ((best_distance == 1 || best_distance == xsize) &&
-          best_length >= 128) {
-        break;
-      }
-    }
-  }
-  *distance_ptr = best_distance;
-  *length_ptr = best_length;
-  return (best_length >= MIN_LENGTH);
-}
-
-static WEBP_INLINE void PushBackCopy(VP8LBackwardRefs* const refs, int length) {
-  int size = refs->size;
-  while (length >= MAX_LENGTH) {
-    refs->refs[size++] = PixOrCopyCreateCopy(1, MAX_LENGTH);
-    length -= MAX_LENGTH;
-  }
-  if (length > 0) {
-    refs->refs[size++] = PixOrCopyCreateCopy(1, length);
-  }
-  refs->size = size;
-}
-
-static void BackwardReferencesRle(int xsize, int ysize,
-                                  const uint32_t* const argb,
-                                  VP8LBackwardRefs* const refs) {
-  const int pix_count = xsize * ysize;
-  int match_len = 0;
-  int i;
-  refs->size = 0;
-  PushBackCopy(refs, match_len);    // i=0 case
-  refs->refs[refs->size++] = PixOrCopyCreateLiteral(argb[0]);
-  for (i = 1; i < pix_count; ++i) {
-    if (argb[i] == argb[i - 1]) {
-      ++match_len;
-    } else {
-      PushBackCopy(refs, match_len);
-      match_len = 0;
-      refs->refs[refs->size++] = PixOrCopyCreateLiteral(argb[i]);
-    }
-  }
-  PushBackCopy(refs, match_len);
-}
-
-static int BackwardReferencesHashChain(int xsize, int ysize,
-                                       const uint32_t* const argb,
-                                       int cache_bits, int quality,
-                                       VP8LBackwardRefs* const refs) {
-  int i;
-  int ok = 0;
-  int cc_init = 0;
-  const int use_color_cache = (cache_bits > 0);
-  const int pix_count = xsize * ysize;
-  HashChain* const hash_chain = (HashChain*)malloc(sizeof(*hash_chain));
-  VP8LColorCache hashers;
-
-  if (hash_chain == NULL) return 0;
-  if (use_color_cache) {
-    cc_init = VP8LColorCacheInit(&hashers, cache_bits);
-    if (!cc_init) goto Error;
-  }
-
-  if (!HashChainInit(hash_chain, pix_count)) goto Error;
-
-  refs->size = 0;
-  for (i = 0; i < pix_count; ) {
-    // Alternative#1: Code the pixels starting at 'i' using backward reference.
-    int offset = 0;
-    int len = 0;
-    if (i < pix_count - 1) {  // FindCopy(i,..) reads pixels at [i] and [i + 1].
-      int maxlen = pix_count - i;
-      if (maxlen > MAX_LENGTH) {
-        maxlen = MAX_LENGTH;
-      }
-      HashChainFindCopy(hash_chain, quality, i, xsize, argb, maxlen,
-                        &offset, &len);
-    }
-    if (len >= MIN_LENGTH) {
-      // Alternative#2: Insert the pixel at 'i' as literal, and code the
-      // pixels starting at 'i + 1' using backward reference.
-      int offset2 = 0;
-      int len2 = 0;
-      int k;
-      HashChainInsert(hash_chain, &argb[i], i);
-      if (i < pix_count - 2) {  // FindCopy(i+1,..) reads [i + 1] and [i + 2].
-        int maxlen = pix_count - (i + 1);
-        if (maxlen > MAX_LENGTH) {
-          maxlen = MAX_LENGTH;
-        }
-        HashChainFindCopy(hash_chain, quality,
-                          i + 1, xsize, argb, maxlen, &offset2, &len2);
-        if (len2 > len + 1) {
-          const uint32_t pixel = argb[i];
-          // Alternative#2 is a better match. So push pixel at 'i' as literal.
-          if (use_color_cache && VP8LColorCacheContains(&hashers, pixel)) {
-            const int ix = VP8LColorCacheGetIndex(&hashers, pixel);
-            refs->refs[refs->size] = PixOrCopyCreateCacheIdx(ix);
-          } else {
-            refs->refs[refs->size] = PixOrCopyCreateLiteral(pixel);
-          }
-          ++refs->size;
-          if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
-          i++;  // Backward reference to be done for next pixel.
-          len = len2;
-          offset = offset2;
-        }
-      }
-      if (len >= MAX_LENGTH) {
-        len = MAX_LENGTH - 1;
-      }
-      refs->refs[refs->size++] = PixOrCopyCreateCopy(offset, len);
-      if (use_color_cache) {
-        for (k = 0; k < len; ++k) {
-          VP8LColorCacheInsert(&hashers, argb[i + k]);
-        }
-      }
-      // Add to the hash_chain (but cannot add the last pixel).
-      {
-        const int last = (len < pix_count - 1 - i) ? len : pix_count - 1 - i;
-        for (k = 1; k < last; ++k) {
-          HashChainInsert(hash_chain, &argb[i + k], i + k);
-        }
-      }
-      i += len;
-    } else {
-      const uint32_t pixel = argb[i];
-      if (use_color_cache && VP8LColorCacheContains(&hashers, pixel)) {
-        // push pixel as a PixOrCopyCreateCacheIdx pixel
-        const int ix = VP8LColorCacheGetIndex(&hashers, pixel);
-        refs->refs[refs->size] = PixOrCopyCreateCacheIdx(ix);
-      } else {
-        refs->refs[refs->size] = PixOrCopyCreateLiteral(pixel);
-      }
-      ++refs->size;
-      if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
-      if (i + 1 < pix_count) {
-        HashChainInsert(hash_chain, &argb[i], i);
-      }
-      ++i;
-    }
-  }
-  ok = 1;
-Error:
-  if (cc_init) VP8LColorCacheClear(&hashers);
-  HashChainDelete(hash_chain);
-  return ok;
-}
-
-// -----------------------------------------------------------------------------
-
-typedef struct {
-  double alpha_[VALUES_IN_BYTE];
-  double red_[VALUES_IN_BYTE];
-  double literal_[PIX_OR_COPY_CODES_MAX];
-  double blue_[VALUES_IN_BYTE];
-  double distance_[NUM_DISTANCE_CODES];
-} CostModel;
-
-static int BackwardReferencesTraceBackwards(
-    int xsize, int ysize, int recursive_cost_model,
-    const uint32_t* const argb, int cache_bits, VP8LBackwardRefs* const refs);
-
-static void ConvertPopulationCountTableToBitEstimates(
-    int num_symbols, const int population_counts[], double output[]) {
-  int sum = 0;
-  int nonzeros = 0;
-  int i;
-  for (i = 0; i < num_symbols; ++i) {
-    sum += population_counts[i];
-    if (population_counts[i] > 0) {
-      ++nonzeros;
-    }
-  }
-  if (nonzeros <= 1) {
-    memset(output, 0, num_symbols * sizeof(*output));
-  } else {
-    const double logsum = VP8LFastLog2(sum);
-    for (i = 0; i < num_symbols; ++i) {
-      output[i] = logsum - VP8LFastLog2(population_counts[i]);
-    }
-  }
-}
-
-static int CostModelBuild(CostModel* const m, int xsize, int ysize,
-                          int recursion_level, const uint32_t* const argb,
-                          int cache_bits) {
-  int ok = 0;
-  VP8LHistogram histo;
-  VP8LBackwardRefs refs;
-  const int quality = 100;
-
-  if (!VP8LBackwardRefsAlloc(&refs, xsize * ysize)) goto Error;
-
-  if (recursion_level > 0) {
-    if (!BackwardReferencesTraceBackwards(xsize, ysize, recursion_level - 1,
-                                          argb, cache_bits, &refs)) {
-      goto Error;
-    }
-  } else {
-    if (!BackwardReferencesHashChain(xsize, ysize, argb, cache_bits, quality,
-                                     &refs)) {
-      goto Error;
-    }
-  }
-  VP8LHistogramCreate(&histo, &refs, cache_bits);
-  ConvertPopulationCountTableToBitEstimates(
-      VP8LHistogramNumCodes(&histo), histo.literal_, m->literal_);
-  ConvertPopulationCountTableToBitEstimates(
-      VALUES_IN_BYTE, histo.red_, m->red_);
-  ConvertPopulationCountTableToBitEstimates(
-      VALUES_IN_BYTE, histo.blue_, m->blue_);
-  ConvertPopulationCountTableToBitEstimates(
-      VALUES_IN_BYTE, histo.alpha_, m->alpha_);
-  ConvertPopulationCountTableToBitEstimates(
-      NUM_DISTANCE_CODES, histo.distance_, m->distance_);
-  ok = 1;
-
- Error:
-  VP8LClearBackwardRefs(&refs);
-  return ok;
-}
-
-static WEBP_INLINE double GetLiteralCost(const CostModel* const m, uint32_t v) {
-  return m->alpha_[v >> 24] +
-         m->red_[(v >> 16) & 0xff] +
-         m->literal_[(v >> 8) & 0xff] +
-         m->blue_[v & 0xff];
-}
-
-static WEBP_INLINE double GetCacheCost(const CostModel* const m, uint32_t idx) {
-  const int literal_idx = VALUES_IN_BYTE + NUM_LENGTH_CODES + idx;
-  return m->literal_[literal_idx];
-}
-
-static WEBP_INLINE double GetLengthCost(const CostModel* const m,
-                                        uint32_t length) {
-  int code, extra_bits_count, extra_bits_value;
-  PrefixEncode(length, &code, &extra_bits_count, &extra_bits_value);
-  return m->literal_[VALUES_IN_BYTE + code] + extra_bits_count;
-}
-
-static WEBP_INLINE double GetDistanceCost(const CostModel* const m,
-                                          uint32_t distance) {
-  int code, extra_bits_count, extra_bits_value;
-  PrefixEncode(distance, &code, &extra_bits_count, &extra_bits_value);
-  return m->distance_[code] + extra_bits_count;
-}
-
-static int BackwardReferencesHashChainDistanceOnly(
-    int xsize, int ysize, int recursive_cost_model, const uint32_t* const argb,
-    int cache_bits, uint32_t* const dist_array) {
-  int i;
-  int ok = 0;
-  int cc_init = 0;
-  const int quality = 100;
-  const int pix_count = xsize * ysize;
-  const int use_color_cache = (cache_bits > 0);
-  double* const cost =
-      (double*)WebPSafeMalloc((uint64_t)pix_count, sizeof(*cost));
-  CostModel* cost_model = (CostModel*)malloc(sizeof(*cost_model));
-  HashChain* hash_chain = (HashChain*)malloc(sizeof(*hash_chain));
-  VP8LColorCache hashers;
-  const double mul0 = (recursive_cost_model != 0) ? 1.0 : 0.68;
-  const double mul1 = (recursive_cost_model != 0) ? 1.0 : 0.82;
-
-  if (cost == NULL || cost_model == NULL || hash_chain == NULL) goto Error;
-
-  if (!HashChainInit(hash_chain, pix_count)) goto Error;
-
-  if (use_color_cache) {
-    cc_init = VP8LColorCacheInit(&hashers, cache_bits);
-    if (!cc_init) goto Error;
-  }
-
-  if (!CostModelBuild(cost_model, xsize, ysize, recursive_cost_model, argb,
-                      cache_bits)) {
-    goto Error;
-  }
-
-  for (i = 0; i < pix_count; ++i) cost[i] = 1e100;
-
-  // We loop one pixel at a time, but store all currently best points to
-  // non-processed locations from this point.
-  dist_array[0] = 0;
-  for (i = 0; i < pix_count; ++i) {
-    double prev_cost = 0.0;
-    int shortmax;
-    if (i > 0) {
-      prev_cost = cost[i - 1];
-    }
-    for (shortmax = 0; shortmax < 2; ++shortmax) {
-      int offset = 0;
-      int len = 0;
-      if (i < pix_count - 1) {  // FindCopy reads pixels at [i] and [i + 1].
-        int maxlen = shortmax ? 2 : MAX_LENGTH;
-        if (maxlen > pix_count - i) {
-          maxlen = pix_count - i;
-        }
-        HashChainFindCopy(hash_chain, quality, i, xsize, argb, maxlen,
-                          &offset, &len);
-      }
-      if (len >= MIN_LENGTH) {
-        const int code = DistanceToPlaneCode(xsize, offset);
-        const double distance_cost =
-            prev_cost + GetDistanceCost(cost_model, code);
-        int k;
-        for (k = 1; k < len; ++k) {
-          const double cost_val =
-              distance_cost + GetLengthCost(cost_model, k);
-          if (cost[i + k] > cost_val) {
-            cost[i + k] = cost_val;
-            dist_array[i + k] = k + 1;
-          }
-        }
-        // This if is for speedup only. It roughly doubles the speed, and
-        // makes compression worse by .1 %.
-        if (len >= 128 && code < 2) {
-          // Long copy for short distances, let's skip the middle
-          // lookups for better copies.
-          // 1) insert the hashes.
-          if (use_color_cache) {
-            for (k = 0; k < len; ++k) {
-              VP8LColorCacheInsert(&hashers, argb[i + k]);
-            }
-          }
-          // 2) Add to the hash_chain (but cannot add the last pixel)
-          {
-            const int last = (len < pix_count - 1 - i) ? len
-                                                       : pix_count - 1 - i;
-            for (k = 0; k < last; ++k) {
-              HashChainInsert(hash_chain, &argb[i + k], i + k);
-            }
-          }
-          // 3) jump.
-          i += len - 1;  // for loop does ++i, thus -1 here.
-          goto next_symbol;
-        }
-      }
-    }
-    if (i < pix_count - 1) {
-      HashChainInsert(hash_chain, &argb[i], i);
-    }
-    {
-      // inserting a literal pixel
-      double cost_val = prev_cost;
-      if (use_color_cache && VP8LColorCacheContains(&hashers, argb[i])) {
-        const int ix = VP8LColorCacheGetIndex(&hashers, argb[i]);
-        cost_val += GetCacheCost(cost_model, ix) * mul0;
-      } else {
-        cost_val += GetLiteralCost(cost_model, argb[i]) * mul1;
-      }
-      if (cost[i] > cost_val) {
-        cost[i] = cost_val;
-        dist_array[i] = 1;  // only one is inserted.
-      }
-      if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
-    }
- next_symbol: ;
-  }
-  // Last pixel still to do, it can only be a single step if not reached
-  // through cheaper means already.
-  ok = 1;
-Error:
-  if (cc_init) VP8LColorCacheClear(&hashers);
-  HashChainDelete(hash_chain);
-  free(cost_model);
-  free(cost);
-  return ok;
-}
-
-static int TraceBackwards(const uint32_t* const dist_array,
-                          int dist_array_size,
-                          uint32_t** const chosen_path,
-                          int* const chosen_path_size) {
-  int i;
-  // Count how many.
-  int count = 0;
-  for (i = dist_array_size - 1; i >= 0; ) {
-    int k = dist_array[i];
-    assert(k >= 1);
-    ++count;
-    i -= k;
-  }
-  // Allocate.
-  *chosen_path_size = count;
-  *chosen_path =
-      (uint32_t*)WebPSafeMalloc((uint64_t)count, sizeof(**chosen_path));
-  if (*chosen_path == NULL) return 0;
-
-  // Write in reverse order.
-  for (i = dist_array_size - 1; i >= 0; ) {
-    int k = dist_array[i];
-    assert(k >= 1);
-    (*chosen_path)[--count] = k;
-    i -= k;
-  }
-  return 1;
-}
-
-static int BackwardReferencesHashChainFollowChosenPath(
-    int xsize, int ysize, const uint32_t* const argb, int cache_bits,
-    const uint32_t* const chosen_path, int chosen_path_size,
-    VP8LBackwardRefs* const refs) {
-  const int quality = 100;
-  const int pix_count = xsize * ysize;
-  const int use_color_cache = (cache_bits > 0);
-  int size = 0;
-  int i = 0;
-  int k;
-  int ix;
-  int ok = 0;
-  int cc_init = 0;
-  HashChain* hash_chain = (HashChain*)malloc(sizeof(*hash_chain));
-  VP8LColorCache hashers;
-
-  if (hash_chain == NULL || !HashChainInit(hash_chain, pix_count)) {
-    goto Error;
-  }
-  if (use_color_cache) {
-    cc_init = VP8LColorCacheInit(&hashers, cache_bits);
-    if (!cc_init) goto Error;
-  }
-
-  refs->size = 0;
-  for (ix = 0; ix < chosen_path_size; ++ix, ++size) {
-    int offset = 0;
-    int len = 0;
-    int maxlen = chosen_path[ix];
-    if (maxlen != 1) {
-      HashChainFindCopy(hash_chain, quality,
-                        i, xsize, argb, maxlen, &offset, &len);
-      assert(len == maxlen);
-      refs->refs[size] = PixOrCopyCreateCopy(offset, len);
-      if (use_color_cache) {
-        for (k = 0; k < len; ++k) {
-          VP8LColorCacheInsert(&hashers, argb[i + k]);
-        }
-      }
-      {
-        const int last = (len < pix_count - 1 - i) ? len : pix_count - 1 - i;
-        for (k = 0; k < last; ++k) {
-          HashChainInsert(hash_chain, &argb[i + k], i + k);
-        }
-      }
-      i += len;
-    } else {
-      if (use_color_cache && VP8LColorCacheContains(&hashers, argb[i])) {
-        // push pixel as a color cache index
-        const int idx = VP8LColorCacheGetIndex(&hashers, argb[i]);
-        refs->refs[size] = PixOrCopyCreateCacheIdx(idx);
-      } else {
-        refs->refs[size] = PixOrCopyCreateLiteral(argb[i]);
-      }
-      if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
-      if (i + 1 < pix_count) {
-        HashChainInsert(hash_chain, &argb[i], i);
-      }
-      ++i;
-    }
-  }
-  assert(size <= refs->max_size);
-  refs->size = size;
-  ok = 1;
-Error:
-  if (cc_init) VP8LColorCacheClear(&hashers);
-  HashChainDelete(hash_chain);
-  return ok;
-}
-
-// Returns 1 on success.
-static int BackwardReferencesTraceBackwards(int xsize, int ysize,
-                                            int recursive_cost_model,
-                                            const uint32_t* const argb,
-                                            int cache_bits,
-                                            VP8LBackwardRefs* const refs) {
-  int ok = 0;
-  const int dist_array_size = xsize * ysize;
-  uint32_t* chosen_path = NULL;
-  int chosen_path_size = 0;
-  uint32_t* dist_array =
-      (uint32_t*)WebPSafeMalloc((uint64_t)dist_array_size, sizeof(*dist_array));
-
-  if (dist_array == NULL) goto Error;
-
-  if (!BackwardReferencesHashChainDistanceOnly(
-      xsize, ysize, recursive_cost_model, argb, cache_bits, dist_array)) {
-    goto Error;
-  }
-  if (!TraceBackwards(dist_array, dist_array_size,
-                      &chosen_path, &chosen_path_size)) {
-    goto Error;
-  }
-  free(dist_array);   // no need to retain this memory any longer
-  dist_array = NULL;
-  if (!BackwardReferencesHashChainFollowChosenPath(
-      xsize, ysize, argb, cache_bits, chosen_path, chosen_path_size, refs)) {
-    goto Error;
-  }
-  ok = 1;
- Error:
-  free(chosen_path);
-  free(dist_array);
-  return ok;
-}
-
-static void BackwardReferences2DLocality(int xsize,
-                                         VP8LBackwardRefs* const refs) {
-  int i;
-  for (i = 0; i < refs->size; ++i) {
-    if (PixOrCopyIsCopy(&refs->refs[i])) {
-      const int dist = refs->refs[i].argb_or_distance;
-      const int transformed_dist = DistanceToPlaneCode(xsize, dist);
-      refs->refs[i].argb_or_distance = transformed_dist;
-    }
-  }
-}
-
-int VP8LGetBackwardReferences(int width, int height,
-                              const uint32_t* const argb,
-                              int quality, int cache_bits, int use_2d_locality,
-                              VP8LBackwardRefs* const best) {
-  int ok = 0;
-  int lz77_is_useful;
-  VP8LBackwardRefs refs_rle, refs_lz77;
-  const int num_pix = width * height;
-
-  VP8LBackwardRefsAlloc(&refs_rle, num_pix);
-  VP8LBackwardRefsAlloc(&refs_lz77, num_pix);
-  VP8LInitBackwardRefs(best);
-  if (refs_rle.refs == NULL || refs_lz77.refs == NULL) {
- Error1:
-    VP8LClearBackwardRefs(&refs_rle);
-    VP8LClearBackwardRefs(&refs_lz77);
-    goto End;
-  }
-
-  if (!BackwardReferencesHashChain(width, height, argb, cache_bits, quality,
-                                   &refs_lz77)) {
-    goto End;
-  }
-  // Backward Reference using RLE only.
-  BackwardReferencesRle(width, height, argb, &refs_rle);
-
-  {
-    double bit_cost_lz77, bit_cost_rle;
-    VP8LHistogram* const histo = (VP8LHistogram*)malloc(sizeof(*histo));
-    if (histo == NULL) goto Error1;
-    // Evaluate lz77 coding
-    VP8LHistogramCreate(histo, &refs_lz77, cache_bits);
-    bit_cost_lz77 = VP8LHistogramEstimateBits(histo);
-    // Evaluate RLE coding
-    VP8LHistogramCreate(histo, &refs_rle, cache_bits);
-    bit_cost_rle = VP8LHistogramEstimateBits(histo);
-    // Decide if LZ77 is useful.
-    lz77_is_useful = (bit_cost_lz77 < bit_cost_rle);
-    free(histo);
-  }
-
-  // Choose appropriate backward reference.
-  if (lz77_is_useful) {
-    // TraceBackwards is costly. Run it for higher qualities.
-    const int try_lz77_trace_backwards = (quality >= 75);
-    *best = refs_lz77;   // default guess: lz77 is better
-    VP8LClearBackwardRefs(&refs_rle);
-    if (try_lz77_trace_backwards) {
-      const int recursion_level = (num_pix < 320 * 200) ? 1 : 0;
-      VP8LBackwardRefs refs_trace;
-      if (!VP8LBackwardRefsAlloc(&refs_trace, num_pix)) {
-        goto End;
-      }
-      if (BackwardReferencesTraceBackwards(
-          width, height, recursion_level, argb, cache_bits, &refs_trace)) {
-        VP8LClearBackwardRefs(&refs_lz77);
-        *best = refs_trace;
-      }
-    }
-  } else {
-    VP8LClearBackwardRefs(&refs_lz77);
-    *best = refs_rle;
-  }
-
-  if (use_2d_locality) BackwardReferences2DLocality(width, best);
-
-  ok = 1;
-
- End:
-  if (!ok) {
-    VP8LClearBackwardRefs(best);
-  }
-  return ok;
-}
-
-// Returns 1 on success.
-static int ComputeCacheHistogram(const uint32_t* const argb,
-                                 int xsize, int ysize,
-                                 const VP8LBackwardRefs* const refs,
-                                 int cache_bits,
-                                 VP8LHistogram* const histo) {
-  int pixel_index = 0;
-  int i;
-  uint32_t k;
-  VP8LColorCache hashers;
-  const int use_color_cache = (cache_bits > 0);
-  int cc_init = 0;
-
-  if (use_color_cache) {
-    cc_init = VP8LColorCacheInit(&hashers, cache_bits);
-    if (!cc_init) return 0;
-  }
-
-  for (i = 0; i < refs->size; ++i) {
-    const PixOrCopy* const v = &refs->refs[i];
-    if (PixOrCopyIsLiteral(v)) {
-      if (use_color_cache &&
-          VP8LColorCacheContains(&hashers, argb[pixel_index])) {
-        // push pixel as a cache index
-        const int ix = VP8LColorCacheGetIndex(&hashers, argb[pixel_index]);
-        const PixOrCopy token = PixOrCopyCreateCacheIdx(ix);
-        VP8LHistogramAddSinglePixOrCopy(histo, &token);
-      } else {
-        VP8LHistogramAddSinglePixOrCopy(histo, v);
-      }
-    } else {
-      VP8LHistogramAddSinglePixOrCopy(histo, v);
-    }
-    if (use_color_cache) {
-      for (k = 0; k < PixOrCopyLength(v); ++k) {
-        VP8LColorCacheInsert(&hashers, argb[pixel_index + k]);
-      }
-    }
-    pixel_index += PixOrCopyLength(v);
-  }
-  assert(pixel_index == xsize * ysize);
-  (void)xsize;  // xsize is not used in non-debug compilations otherwise.
-  (void)ysize;  // ysize is not used in non-debug compilations otherwise.
-  if (cc_init) VP8LColorCacheClear(&hashers);
-  return 1;
-}
-
-// Returns how many bits are to be used for a color cache.
-int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
-                                      int xsize, int ysize,
-                                      int* const best_cache_bits) {
-  int ok = 0;
-  int cache_bits;
-  double lowest_entropy = 1e99;
-  VP8LBackwardRefs refs;
-  static const double kSmallPenaltyForLargeCache = 4.0;
-  static const int quality = 30;
-  if (!VP8LBackwardRefsAlloc(&refs, xsize * ysize) ||
-      !BackwardReferencesHashChain(xsize, ysize, argb, 0, quality, &refs)) {
-    goto Error;
-  }
-  for (cache_bits = 0; cache_bits <= MAX_COLOR_CACHE_BITS; ++cache_bits) {
-    double cur_entropy;
-    VP8LHistogram histo;
-    VP8LHistogramInit(&histo, cache_bits);
-    ComputeCacheHistogram(argb, xsize, ysize, &refs, cache_bits, &histo);
-    cur_entropy = VP8LHistogramEstimateBits(&histo) +
-        kSmallPenaltyForLargeCache * cache_bits;
-    if (cache_bits == 0 || cur_entropy < lowest_entropy) {
-      *best_cache_bits = cache_bits;
-      lowest_entropy = cur_entropy;
-    }
-  }
-  ok = 1;
- Error:
-  VP8LClearBackwardRefs(&refs);
-  return ok;
-}