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// Copyright 2012 Google Inc. All Rights Reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
// Author: Jyrki Alakuijala (
#include <assert.h>
#include <stdlib.h>
#include "../webp/types.h"
#include "../webp/format_constants.h"
#ifdef __cplusplus
extern "C" {
// The maximum allowed limit is 11.
// -----------------------------------------------------------------------------
// PixOrCopy
enum Mode {
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;
// -----------------------------------------------------------------------------
// VP8LHashChain
#define HASH_BITS 18
#define HASH_SIZE (1 << HASH_BITS)
typedef struct VP8LHashChain VP8LHashChain;
struct VP8LHashChain {
// The 20 most significant bits contain the offset at which the best match
// is found. These 20 bits are the limit defined by GetWindowSizeForHashChain
// (through WINDOW_SIZE = 1<<20).
// The lower 12 bits contain the length of the match. The 12 bit limit is
// defined in MaxFindCopyLength with MAX_LENGTH=4096.
uint32_t* offset_length_;
// This is the maximum size of the hash_chain that can be constructed.
// Typically this is the pixel count (width x height) for a given image.
int size_;
// Must be called first, to set size.
int VP8LHashChainInit(VP8LHashChain* const p, int size);
// Pre-compute the best matches for argb.
int VP8LHashChainFill(VP8LHashChain* const p, int quality,
const uint32_t* const argb, int xsize, int ysize,
int low_effort);
void VP8LHashChainClear(VP8LHashChain* const p); // release memory
// -----------------------------------------------------------------------------
// VP8LBackwardRefs (block-based backward-references storage)
// maximum number of reference blocks the image will be segmented into
typedef struct PixOrCopyBlock PixOrCopyBlock; // forward declaration
typedef struct VP8LBackwardRefs VP8LBackwardRefs;
// Container for blocks chain
struct VP8LBackwardRefs {
int block_size_; // common block-size
int error_; // set to true if some memory error occurred
PixOrCopyBlock* refs_; // list of currently used blocks
PixOrCopyBlock** tail_; // for list recycling
PixOrCopyBlock* free_blocks_; // free-list
PixOrCopyBlock* last_block_; // used for adding new refs (internal)
// Initialize the object. 'block_size' is the common block size to store
// references (typically, width * height / MAX_REFS_BLOCK_PER_IMAGE).
void VP8LBackwardRefsInit(VP8LBackwardRefs* const refs, int block_size);
// Release memory for backward references.
void VP8LBackwardRefsClear(VP8LBackwardRefs* const refs);
// Copies the 'src' backward refs to the 'dst'. Returns 0 in case of error.
int VP8LBackwardRefsCopy(const VP8LBackwardRefs* const src,
VP8LBackwardRefs* const dst);
// Cursor for iterating on references content
typedef struct {
// public:
PixOrCopy* cur_pos; // current position
// private:
PixOrCopyBlock* cur_block_; // current block in the refs list
const PixOrCopy* last_pos_; // sentinel for switching to next block
} VP8LRefsCursor;
// Returns a cursor positioned at the beginning of the references list.
VP8LRefsCursor VP8LRefsCursorInit(const VP8LBackwardRefs* const refs);
// Returns true if cursor is pointing at a valid position.
static WEBP_INLINE int VP8LRefsCursorOk(const VP8LRefsCursor* const c) {
return (c->cur_pos != NULL);
// Move to next block of references. Internal, not to be called directly.
void VP8LRefsCursorNextBlock(VP8LRefsCursor* const c);
// Move to next position, or NULL. Should not be called if !VP8LRefsCursorOk().
static WEBP_INLINE void VP8LRefsCursorNext(VP8LRefsCursor* const c) {
assert(c != NULL);
if (++c->cur_pos == c->last_pos_) VP8LRefsCursorNextBlock(c);
// -----------------------------------------------------------------------------
// Main entry points
// Evaluates best possible backward references for specified quality.
// The input cache_bits to 'VP8LGetBackwardReferences' sets the maximum cache
// bits to use (passing 0 implies disabling the local color cache).
// The optimal cache bits is evaluated and set for the *cache_bits parameter.
// The return value is the pointer to the best of the two backward refs viz,
// refs[0] or refs[1].
VP8LBackwardRefs* VP8LGetBackwardReferences(
int width, int height, const uint32_t* const argb, int quality,
int low_effort, int* const cache_bits,
const VP8LHashChain* const hash_chain, VP8LBackwardRefs refs[2]);
#ifdef __cplusplus