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// 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)
//
#ifndef WEBP_ENC_BACKWARD_REFERENCES_H_
#define WEBP_ENC_BACKWARD_REFERENCES_H_
#include <assert.h>
#include <stdlib.h>
#include "../webp/types.h"
#include "../webp/format_constants.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
// The spec allows 11, we use 9 bits to reduce memory consumption in encoding.
// Having 9 instead of 11 only removes about 0.25 % of compression density.
#define MAX_COLOR_CACHE_BITS 9
// Max ever number of codes we'll use:
#define PIX_OR_COPY_CODES_MAX \
(NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS))
// -----------------------------------------------------------------------------
// PrefixEncode()
// use GNU builtins where available.
#if defined(__GNUC__) && \
((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
return n == 0 ? -1 : 31 ^ __builtin_clz(n);
}
#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86))
#include <intrin.h>
#pragma intrinsic(_BitScanReverse)
static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
unsigned long first_set_bit;
return _BitScanReverse(&first_set_bit, n) ? first_set_bit : -1;
}
#else
static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
int log = 0;
uint32_t value = n;
int i;
if (value == 0) return -1;
for (i = 4; i >= 0; --i) {
const int shift = (1 << i);
const uint32_t x = value >> shift;
if (x != 0) {
value = x;
log += shift;
}
}
return log;
}
#endif
static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) {
const int floor = BitsLog2Floor(n);
if (n == (n & ~(n - 1))) // zero or a power of two.
return floor;
else
return floor + 1;
}
// Splitting of distance and length codes into prefixes and
// extra bits. The prefixes are encoded with an entropy code
// while the extra bits are stored just as normal bits.
static WEBP_INLINE void PrefixEncode(int distance, int* const code,
int* const extra_bits_count,
int* const extra_bits_value) {
// Collect the two most significant bits where the highest bit is 1.
const int highest_bit = BitsLog2Floor(--distance);
// & 0x3f is to make behavior well defined when highest_bit
// does not exist or is the least significant bit.
const int second_highest_bit =
(distance >> ((highest_bit - 1) & 0x3f)) & 1;
*extra_bits_count = (highest_bit > 0) ? (highest_bit - 1) : 0;
*extra_bits_value = distance & ((1 << *extra_bits_count) - 1);
*code = (highest_bit > 0) ? (2 * highest_bit + second_highest_bit)
: (highest_bit == 0) ? 1 : 0;
}
// -----------------------------------------------------------------------------
// PixOrCopy
enum Mode {
kLiteral,
kCacheIdx,
kCopy,
kNone
};
typedef struct {
// mode as uint8_t to make the memory layout to be exactly 8 bytes.
uint8_t mode;
uint16_t len;
uint32_t argb_or_distance;
} PixOrCopy;
static WEBP_INLINE PixOrCopy PixOrCopyCreateCopy(uint32_t distance,
uint16_t len) {
PixOrCopy retval;
retval.mode = kCopy;
retval.argb_or_distance = distance;
retval.len = len;
return retval;
}
static WEBP_INLINE PixOrCopy PixOrCopyCreateCacheIdx(int idx) {
PixOrCopy retval;
assert(idx >= 0);
assert(idx < (1 << MAX_COLOR_CACHE_BITS));
retval.mode = kCacheIdx;
retval.argb_or_distance = idx;
retval.len = 1;
return retval;
}
static WEBP_INLINE PixOrCopy PixOrCopyCreateLiteral(uint32_t argb) {
PixOrCopy retval;
retval.mode = kLiteral;
retval.argb_or_distance = argb;
retval.len = 1;
return retval;
}
static WEBP_INLINE int PixOrCopyIsLiteral(const PixOrCopy* const p) {
return (p->mode == kLiteral);
}
static WEBP_INLINE int PixOrCopyIsCacheIdx(const PixOrCopy* const p) {
return (p->mode == kCacheIdx);
}
static WEBP_INLINE int PixOrCopyIsCopy(const PixOrCopy* const p) {
return (p->mode == kCopy);
}
static WEBP_INLINE uint32_t PixOrCopyLiteral(const PixOrCopy* const p,
int component) {
assert(p->mode == kLiteral);
return (p->argb_or_distance >> (component * 8)) & 0xff;
}
static WEBP_INLINE uint32_t PixOrCopyLength(const PixOrCopy* const p) {
return p->len;
}
static WEBP_INLINE uint32_t PixOrCopyArgb(const PixOrCopy* const p) {
assert(p->mode == kLiteral);
return p->argb_or_distance;
}
static WEBP_INLINE uint32_t PixOrCopyCacheIdx(const PixOrCopy* const p) {
assert(p->mode == kCacheIdx);
assert(p->argb_or_distance < (1U << MAX_COLOR_CACHE_BITS));
return p->argb_or_distance;
}
static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) {
assert(p->mode == kCopy);
return p->argb_or_distance;
}
// -----------------------------------------------------------------------------
// VP8LBackwardRefs
typedef struct {
PixOrCopy* refs;
int size; // currently used
int max_size; // maximum capacity
} VP8LBackwardRefs;
// Initialize the object. Must be called first. 'refs' can be NULL.
void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs);
// Release memory and re-initialize the object. 'refs' can be NULL.
void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs);
// Allocate 'max_size' references. Returns false in case of memory error.
int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size);
// -----------------------------------------------------------------------------
// Main entry points
// Evaluates best possible backward references for specified quality.
// Further optimize for 2D locality if use_2d_locality flag is set.
int VP8LGetBackwardReferences(int width, int height,
const uint32_t* const argb,
int quality, int cache_bits, int use_2d_locality,
VP8LBackwardRefs* const best);
// Produce an estimate for a good color cache size for the image.
int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
int xsize, int ysize,
int* const best_cache_bits);
#if defined(__cplusplus) || defined(c_plusplus)
}
#endif
#endif // WEBP_ENC_BACKWARD_REFERENCES_H_
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