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Nagram/TMessagesProj/jni/libwebp/enc/backward_references.c
DrKLO 2073ead37e Update to 2.3.0
2015-01-03 01:15:07 +03:00

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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 (jyrki@google.com)
//
#include <assert.h>
#include <math.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_MULTIPLIER (0xc6a4a7935bd1e995ULL)
#define MIN_BLOCK_SIZE 256 // minimum block size for backward references
#define MAX_ENTROPY (1e30f)
// 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
// -----------------------------------------------------------------------------
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
struct PixOrCopyBlock {
PixOrCopyBlock* next_; // next block (or NULL)
PixOrCopy* start_; // data start
int size_; // currently used size
};
static void ClearBackwardRefs(VP8LBackwardRefs* const refs) {
assert(refs != NULL);
if (refs->tail_ != NULL) {
*refs->tail_ = refs->free_blocks_; // recycle all blocks at once
}
refs->free_blocks_ = refs->refs_;
refs->tail_ = &refs->refs_;
refs->last_block_ = NULL;
refs->refs_ = NULL;
}
void VP8LBackwardRefsClear(VP8LBackwardRefs* const refs) {
assert(refs != NULL);
ClearBackwardRefs(refs);
while (refs->free_blocks_ != NULL) {
PixOrCopyBlock* const next = refs->free_blocks_->next_;
WebPSafeFree(refs->free_blocks_);
refs->free_blocks_ = next;
}
}
void VP8LBackwardRefsInit(VP8LBackwardRefs* const refs, int block_size) {
assert(refs != NULL);
memset(refs, 0, sizeof(*refs));
refs->tail_ = &refs->refs_;
refs->block_size_ =
(block_size < MIN_BLOCK_SIZE) ? MIN_BLOCK_SIZE : block_size;
}
VP8LRefsCursor VP8LRefsCursorInit(const VP8LBackwardRefs* const refs) {
VP8LRefsCursor c;
c.cur_block_ = refs->refs_;
if (refs->refs_ != NULL) {
c.cur_pos = c.cur_block_->start_;
c.last_pos_ = c.cur_pos + c.cur_block_->size_;
} else {
c.cur_pos = NULL;
c.last_pos_ = NULL;
}
return c;
}
void VP8LRefsCursorNextBlock(VP8LRefsCursor* const c) {
PixOrCopyBlock* const b = c->cur_block_->next_;
c->cur_pos = (b == NULL) ? NULL : b->start_;
c->last_pos_ = (b == NULL) ? NULL : b->start_ + b->size_;
c->cur_block_ = b;
}
// Create a new block, either from the free list or allocated
static PixOrCopyBlock* BackwardRefsNewBlock(VP8LBackwardRefs* const refs) {
PixOrCopyBlock* b = refs->free_blocks_;
if (b == NULL) { // allocate new memory chunk
const size_t total_size =
sizeof(*b) + refs->block_size_ * sizeof(*b->start_);
b = (PixOrCopyBlock*)WebPSafeMalloc(1ULL, total_size);
if (b == NULL) {
refs->error_ |= 1;
return NULL;
}
b->start_ = (PixOrCopy*)((uint8_t*)b + sizeof(*b)); // not always aligned
} else { // recycle from free-list
refs->free_blocks_ = b->next_;
}
*refs->tail_ = b;
refs->tail_ = &b->next_;
refs->last_block_ = b;
b->next_ = NULL;
b->size_ = 0;
return b;
}
static WEBP_INLINE void BackwardRefsCursorAdd(VP8LBackwardRefs* const refs,
const PixOrCopy v) {
PixOrCopyBlock* b = refs->last_block_;
if (b == NULL || b->size_ == refs->block_size_) {
b = BackwardRefsNewBlock(refs);
if (b == NULL) return; // refs->error_ is set
}
b->start_[b->size_++] = v;
}
int VP8LBackwardRefsCopy(const VP8LBackwardRefs* const src,
VP8LBackwardRefs* const dst) {
const PixOrCopyBlock* b = src->refs_;
ClearBackwardRefs(dst);
assert(src->block_size_ == dst->block_size_);
while (b != NULL) {
PixOrCopyBlock* const new_b = BackwardRefsNewBlock(dst);
if (new_b == NULL) return 0; // dst->error_ is set
memcpy(new_b->start_, b->start_, b->size_ * sizeof(*b->start_));
new_b->size_ = b->size_;
b = b->next_;
}
return 1;
}
// -----------------------------------------------------------------------------
// Hash chains
// initialize as empty
static void HashChainInit(VP8LHashChain* const p) {
int i;
assert(p != NULL);
for (i = 0; i < p->size_; ++i) {
p->chain_[i] = -1;
}
for (i = 0; i < HASH_SIZE; ++i) {
p->hash_to_first_index_[i] = -1;
}
}
int VP8LHashChainInit(VP8LHashChain* const p, int size) {
assert(p->size_ == 0);
assert(p->chain_ == NULL);
assert(size > 0);
p->chain_ = (int*)WebPSafeMalloc(size, sizeof(*p->chain_));
if (p->chain_ == NULL) return 0;
p->size_ = size;
HashChainInit(p);
return 1;
}
void VP8LHashChainClear(VP8LHashChain* const p) {
assert(p != NULL);
WebPSafeFree(p->chain_);
p->size_ = 0;
p->chain_ = NULL;
}
// -----------------------------------------------------------------------------
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;
}
// Insertion of two pixels at a time.
static void HashChainInsert(VP8LHashChain* 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 void GetParamsForHashChainFindCopy(int quality, int xsize,
int cache_bits, int* window_size,
int* iter_pos, int* iter_limit) {
const int iter_mult = (quality < 27) ? 1 : 1 + ((quality - 27) >> 4);
const int iter_neg = -iter_mult * (quality >> 1);
// Limit the backward-ref window size for lower qualities.
const int max_window_size = (quality > 50) ? WINDOW_SIZE
: (quality > 25) ? (xsize << 8)
: (xsize << 4);
assert(xsize > 0);
*window_size = (max_window_size > WINDOW_SIZE) ? WINDOW_SIZE
: max_window_size;
*iter_pos = 8 + (quality >> 3);
// For lower entropy images, the rigorous search loop in HashChainFindCopy
// can be relaxed.
*iter_limit = (cache_bits > 0) ? iter_neg : iter_neg / 2;
}
static int HashChainFindCopy(const VP8LHashChain* const p,
int base_position, int xsize_signed,
const uint32_t* const argb, int max_len,
int window_size, int iter_pos, int iter_limit,
int* const distance_ptr,
int* const length_ptr) {
const uint32_t* const argb_start = argb + base_position;
uint64_t best_val = 0;
uint32_t best_length = 1;
uint32_t best_distance = 0;
const uint32_t xsize = (uint32_t)xsize_signed;
const int min_pos =
(base_position > window_size) ? base_position - window_size : 0;
int pos;
assert(xsize > 0);
if (max_len > MAX_LENGTH) {
max_len = MAX_LENGTH;
}
for (pos = p->hash_to_first_index_[GetPixPairHash64(argb_start)];
pos >= min_pos;
pos = p->chain_[pos]) {
uint64_t val;
uint32_t curr_length;
uint32_t distance;
const uint32_t* const ptr1 = (argb + pos + best_length - 1);
const uint32_t* const ptr2 = (argb_start + best_length - 1);
if (iter_pos < 0) {
if (iter_pos < iter_limit || best_val >= 0xff0000) {
break;
}
}
--iter_pos;
// Before 'expensive' linear match, check if the two arrays match at the
// current best length index and also for the succeeding elements.
if (ptr1[0] != ptr2[0] || ptr1[1] != ptr2[1]) continue;
curr_length = FindMatchLength(argb + pos, argb_start, max_len);
if (curr_length < best_length) continue;
distance = (uint32_t)(base_position - pos);
val = curr_length << 16;
// Favoring 2d locality here gives savings for certain images.
if (distance < 9 * xsize) {
const uint32_t y = distance / xsize;
uint32_t x = distance % xsize;
if (x > (xsize >> 1)) {
x = xsize - x;
}
if (x <= 7) {
val += 9 * 9 + 9 * 9;
val -= y * y + x * x;
}
}
if (best_val < val) {
best_val = val;
best_length = curr_length;
best_distance = distance;
if (curr_length >= (uint32_t)max_len) {
break;
}
if ((best_distance == 1 || distance == xsize) &&
best_length >= 128) {
break;
}
}
}
*distance_ptr = (int)best_distance;
*length_ptr = best_length;
return (best_length >= MIN_LENGTH);
}
static WEBP_INLINE void PushBackCopy(VP8LBackwardRefs* const refs, int length) {
while (length >= MAX_LENGTH) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(1, MAX_LENGTH));
length -= MAX_LENGTH;
}
if (length > 0) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(1, length));
}
}
static int 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;
ClearBackwardRefs(refs);
PushBackCopy(refs, match_len); // i=0 case
BackwardRefsCursorAdd(refs, 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;
BackwardRefsCursorAdd(refs, PixOrCopyCreateLiteral(argb[i]));
}
}
PushBackCopy(refs, match_len);
return !refs->error_;
}
static int BackwardReferencesHashChain(int xsize, int ysize,
const uint32_t* const argb,
int cache_bits, int quality,
VP8LHashChain* const hash_chain,
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;
VP8LColorCache hashers;
int window_size = WINDOW_SIZE;
int iter_pos = 1;
int iter_limit = -1;
if (use_color_cache) {
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) goto Error;
}
ClearBackwardRefs(refs);
GetParamsForHashChainFindCopy(quality, xsize, cache_bits,
&window_size, &iter_pos, &iter_limit);
HashChainInit(hash_chain);
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 max_len = pix_count - i;
HashChainFindCopy(hash_chain, i, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&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 max_len = pix_count - (i + 1);
HashChainFindCopy(hash_chain, i + 1, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&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.
PixOrCopy v;
if (use_color_cache && VP8LColorCacheContains(&hashers, pixel)) {
const int ix = VP8LColorCacheGetIndex(&hashers, pixel);
v = PixOrCopyCreateCacheIdx(ix);
} else {
if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
v = PixOrCopyCreateLiteral(pixel);
}
BackwardRefsCursorAdd(refs, v);
i++; // Backward reference to be done for next pixel.
len = len2;
offset = offset2;
}
}
if (len >= MAX_LENGTH) {
len = MAX_LENGTH - 1;
}
BackwardRefsCursorAdd(refs, 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];
PixOrCopy v;
if (use_color_cache && VP8LColorCacheContains(&hashers, pixel)) {
// push pixel as a PixOrCopyCreateCacheIdx pixel
const int ix = VP8LColorCacheGetIndex(&hashers, pixel);
v = PixOrCopyCreateCacheIdx(ix);
} else {
if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
v = PixOrCopyCreateLiteral(pixel);
}
BackwardRefsCursorAdd(refs, v);
if (i + 1 < pix_count) {
HashChainInsert(hash_chain, &argb[i], i);
}
++i;
}
}
ok = !refs->error_;
Error:
if (cc_init) VP8LColorCacheClear(&hashers);
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 quality, int cache_bits,
VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs);
static void ConvertPopulationCountTableToBitEstimates(
int num_symbols, const uint32_t population_counts[], double output[]) {
uint32_t 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 quality, int cache_bits,
VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs) {
int ok = 0;
VP8LHistogram* histo = NULL;
ClearBackwardRefs(refs);
if (recursion_level > 0) {
if (!BackwardReferencesTraceBackwards(xsize, ysize, recursion_level - 1,
argb, quality, cache_bits, hash_chain,
refs)) {
goto Error;
}
} else {
if (!BackwardReferencesHashChain(xsize, ysize, argb, cache_bits, quality,
hash_chain, refs)) {
goto Error;
}
}
histo = VP8LAllocateHistogram(cache_bits);
if (histo == NULL) goto Error;
VP8LHistogramCreate(histo, refs, cache_bits);
ConvertPopulationCountTableToBitEstimates(
VP8LHistogramNumCodes(histo->palette_code_bits_),
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:
VP8LFreeHistogram(histo);
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;
VP8LPrefixEncodeBits(length, &code, &extra_bits);
return m->literal_[VALUES_IN_BYTE + code] + extra_bits;
}
static WEBP_INLINE double GetDistanceCost(const CostModel* const m,
uint32_t distance) {
int code, extra_bits;
VP8LPrefixEncodeBits(distance, &code, &extra_bits);
return m->distance_[code] + extra_bits;
}
static int BackwardReferencesHashChainDistanceOnly(
int xsize, int ysize, int recursive_cost_model, const uint32_t* const argb,
int quality, int cache_bits, VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs, uint32_t* const dist_array) {
int i;
int ok = 0;
int cc_init = 0;
const int pix_count = xsize * ysize;
const int use_color_cache = (cache_bits > 0);
float* const cost =
(float*)WebPSafeMalloc(pix_count, sizeof(*cost));
CostModel* cost_model = (CostModel*)WebPSafeMalloc(1ULL, sizeof(*cost_model));
VP8LColorCache hashers;
const double mul0 = (recursive_cost_model != 0) ? 1.0 : 0.68;
const double mul1 = (recursive_cost_model != 0) ? 1.0 : 0.82;
const int min_distance_code = 2; // TODO(vikasa): tune as function of quality
int window_size = WINDOW_SIZE;
int iter_pos = 1;
int iter_limit = -1;
if (cost == NULL || cost_model == NULL) 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,
quality, cache_bits, hash_chain, refs)) {
goto Error;
}
for (i = 0; i < pix_count; ++i) cost[i] = 1e38f;
// We loop one pixel at a time, but store all currently best points to
// non-processed locations from this point.
dist_array[0] = 0;
GetParamsForHashChainFindCopy(quality, xsize, cache_bits,
&window_size, &iter_pos, &iter_limit);
HashChainInit(hash_chain);
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 max_len = shortmax ? 2 : pix_count - i;
HashChainFindCopy(hash_chain, i, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&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] = (float)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 <= min_distance_code) {
// 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 + i < pix_count - 1) ? len + i
: pix_count - 1;
for (k = i; k < last; ++k) {
HashChainInsert(hash_chain, &argb[k], 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 {
if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
cost_val += GetLiteralCost(cost_model, argb[i]) * mul1;
}
if (cost[i] > cost_val) {
cost[i] = (float)cost_val;
dist_array[i] = 1; // only one is inserted.
}
}
next_symbol: ;
}
// Last pixel still to do, it can only be a single step if not reached
// through cheaper means already.
ok = !refs->error_;
Error:
if (cc_init) VP8LColorCacheClear(&hashers);
WebPSafeFree(cost_model);
WebPSafeFree(cost);
return ok;
}
// We pack the path at the end of *dist_array and return
// a pointer to this part of the array. Example:
// dist_array = [1x2xx3x2] => packed [1x2x1232], chosen_path = [1232]
static void TraceBackwards(uint32_t* const dist_array,
int dist_array_size,
uint32_t** const chosen_path,
int* const chosen_path_size) {
uint32_t* path = dist_array + dist_array_size;
uint32_t* cur = dist_array + dist_array_size - 1;
while (cur >= dist_array) {
const int k = *cur;
--path;
*path = k;
cur -= k;
}
*chosen_path = path;
*chosen_path_size = (int)(dist_array + dist_array_size - path);
}
static int BackwardReferencesHashChainFollowChosenPath(
int xsize, int ysize, const uint32_t* const argb,
int quality, int cache_bits,
const uint32_t* const chosen_path, int chosen_path_size,
VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs) {
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;
int window_size = WINDOW_SIZE;
int iter_pos = 1;
int iter_limit = -1;
VP8LColorCache hashers;
if (use_color_cache) {
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) goto Error;
}
ClearBackwardRefs(refs);
GetParamsForHashChainFindCopy(quality, xsize, cache_bits,
&window_size, &iter_pos, &iter_limit);
HashChainInit(hash_chain);
for (ix = 0; ix < chosen_path_size; ++ix, ++size) {
int offset = 0;
int len = 0;
int max_len = chosen_path[ix];
if (max_len != 1) {
HashChainFindCopy(hash_chain, i, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&offset, &len);
assert(len == max_len);
BackwardRefsCursorAdd(refs, 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 {
PixOrCopy v;
if (use_color_cache && VP8LColorCacheContains(&hashers, argb[i])) {
// push pixel as a color cache index
const int idx = VP8LColorCacheGetIndex(&hashers, argb[i]);
v = PixOrCopyCreateCacheIdx(idx);
} else {
if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
v = PixOrCopyCreateLiteral(argb[i]);
}
BackwardRefsCursorAdd(refs, v);
if (i + 1 < pix_count) {
HashChainInsert(hash_chain, &argb[i], i);
}
++i;
}
}
ok = !refs->error_;
Error:
if (cc_init) VP8LColorCacheClear(&hashers);
return ok;
}
// Returns 1 on success.
static int BackwardReferencesTraceBackwards(int xsize, int ysize,
int recursive_cost_model,
const uint32_t* const argb,
int quality, int cache_bits,
VP8LHashChain* const hash_chain,
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(dist_array_size, sizeof(*dist_array));
if (dist_array == NULL) goto Error;
if (!BackwardReferencesHashChainDistanceOnly(
xsize, ysize, recursive_cost_model, argb, quality, cache_bits, hash_chain,
refs, dist_array)) {
goto Error;
}
TraceBackwards(dist_array, dist_array_size, &chosen_path, &chosen_path_size);
if (!BackwardReferencesHashChainFollowChosenPath(
xsize, ysize, argb, quality, cache_bits, chosen_path, chosen_path_size,
hash_chain, refs)) {
goto Error;
}
ok = 1;
Error:
WebPSafeFree(dist_array);
return ok;
}
static void BackwardReferences2DLocality(int xsize,
const VP8LBackwardRefs* const refs) {
VP8LRefsCursor c = VP8LRefsCursorInit(refs);
while (VP8LRefsCursorOk(&c)) {
if (PixOrCopyIsCopy(c.cur_pos)) {
const int dist = c.cur_pos->argb_or_distance;
const int transformed_dist = DistanceToPlaneCode(xsize, dist);
c.cur_pos->argb_or_distance = transformed_dist;
}
VP8LRefsCursorNext(&c);
}
}
VP8LBackwardRefs* VP8LGetBackwardReferences(
int width, int height, const uint32_t* const argb, int quality,
int cache_bits, int use_2d_locality, VP8LHashChain* const hash_chain,
VP8LBackwardRefs refs_array[2]) {
int lz77_is_useful;
const int num_pix = width * height;
VP8LBackwardRefs* best = NULL;
VP8LBackwardRefs* const refs_lz77 = &refs_array[0];
VP8LBackwardRefs* const refs_rle = &refs_array[1];
if (!BackwardReferencesHashChain(width, height, argb, cache_bits, quality,
hash_chain, refs_lz77)) {
return NULL;
}
if (!BackwardReferencesRle(width, height, argb, refs_rle)) {
return NULL;
}
{
double bit_cost_lz77, bit_cost_rle;
VP8LHistogram* const histo = VP8LAllocateHistogram(cache_bits);
if (histo == NULL) return NULL;
// 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);
VP8LFreeHistogram(histo);
}
// Choose appropriate backward reference.
if (lz77_is_useful) {
// TraceBackwards is costly. Don't execute it at lower quality.
const int try_lz77_trace_backwards = (quality >= 25);
best = refs_lz77; // default guess: lz77 is better
if (try_lz77_trace_backwards) {
// Set recursion level for large images using a color cache.
const int recursion_level =
(num_pix < 320 * 200) && (cache_bits > 0) ? 1 : 0;
VP8LBackwardRefs* const refs_trace = &refs_array[1];
ClearBackwardRefs(refs_trace);
if (BackwardReferencesTraceBackwards(width, height, recursion_level, argb,
quality, cache_bits, hash_chain,
refs_trace)) {
best = refs_trace;
}
}
} else {
best = refs_rle;
}
if (use_2d_locality) BackwardReferences2DLocality(width, best);
return best;
}
// Returns entropy for the given cache bits.
static double ComputeCacheEntropy(const uint32_t* const argb,
int xsize, int ysize,
const VP8LBackwardRefs* const refs,
int cache_bits) {
int pixel_index = 0;
uint32_t k;
const int use_color_cache = (cache_bits > 0);
int cc_init = 0;
double entropy = MAX_ENTROPY;
const double kSmallPenaltyForLargeCache = 4.0;
VP8LColorCache hashers;
VP8LRefsCursor c = VP8LRefsCursorInit(refs);
VP8LHistogram* histo = VP8LAllocateHistogram(cache_bits);
if (histo == NULL) goto Error;
if (use_color_cache) {
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) goto Error;
}
while (VP8LRefsCursorOk(&c)) {
const PixOrCopy* const v = c.cur_pos;
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);
VP8LRefsCursorNext(&c);
}
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.
entropy = VP8LHistogramEstimateBits(histo) +
kSmallPenaltyForLargeCache * cache_bits;
Error:
if (cc_init) VP8LColorCacheClear(&hashers);
VP8LFreeHistogram(histo);
return entropy;
}
// *best_cache_bits will contain how many bits are to be used for a color cache.
// Returns 0 in case of memory error.
int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
int xsize, int ysize, int quality,
VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs,
int* const best_cache_bits) {
int eval_low = 1;
int eval_high = 1;
double entropy_low = MAX_ENTROPY;
double entropy_high = MAX_ENTROPY;
int cache_bits_low = 0;
int cache_bits_high = MAX_COLOR_CACHE_BITS;
if (!BackwardReferencesHashChain(xsize, ysize, argb, 0, quality, hash_chain,
refs)) {
return 0;
}
// Do a binary search to find the optimal entropy for cache_bits.
while (cache_bits_high - cache_bits_low > 1) {
if (eval_low) {
entropy_low =
ComputeCacheEntropy(argb, xsize, ysize, refs, cache_bits_low);
eval_low = 0;
}
if (eval_high) {
entropy_high =
ComputeCacheEntropy(argb, xsize, ysize, refs, cache_bits_high);
eval_high = 0;
}
if (entropy_high < entropy_low) {
*best_cache_bits = cache_bits_high;
cache_bits_low = (cache_bits_low + cache_bits_high) / 2;
eval_low = 1;
} else {
*best_cache_bits = cache_bits_low;
cache_bits_high = (cache_bits_low + cache_bits_high) / 2;
eval_high = 1;
}
}
return 1;
}
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