// 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 "../dsp/dsp.h"
#include "../utils/color_cache.h"
#include "../utils/utils.h"
#define VALUES_IN_BYTE 256
#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;
}
// Returns the exact index where array1 and array2 are different if this
// index is strictly superior to best_len_match. Otherwise, it returns 0.
// If no two elements are the same, it returns max_limit.
static WEBP_INLINE int FindMatchLength(const uint32_t* const array1,
const uint32_t* const array2,
int best_len_match,
int max_limit) {
int match_len;
// Before 'expensive' linear match, check if the two arrays match at the
// current best length index.
if (array1[best_len_match] != array2[best_len_match]) return 0;
#if defined(WEBP_USE_SSE2)
// Check if anything is different up to best_len_match excluded.
// memcmp seems to be slower on ARM so it is disabled for now.
if (memcmp(array1, array2, best_len_match * sizeof(*array1))) return 0;
match_len = best_len_match + 1;
#else
match_len = 0;
#endif
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 HashChainReset(VP8LHashChain* const p) {
assert(p != NULL);
// Set the int32_t arrays to -1.
memset(p->chain_, 0xff, p->size_ * sizeof(*p->chain_));
memset(p->hash_to_first_index_, 0xff,
HASH_SIZE * sizeof(*p->hash_to_first_index_));
}
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;
HashChainReset(p);
return 1;
}
void VP8LHashChainClear(VP8LHashChain* const p) {
assert(p != NULL);
WebPSafeFree(p->chain_);
p->size_ = 0;
p->chain_ = NULL;
}
// -----------------------------------------------------------------------------
#define HASH_MULTIPLIER_HI (0xc6a4a793U)
#define HASH_MULTIPLIER_LO (0x5bd1e996U)
static WEBP_INLINE uint32_t GetPixPairHash64(const uint32_t* const argb) {
uint32_t key;
key = argb[1] * HASH_MULTIPLIER_HI;
key += argb[0] * HASH_MULTIPLIER_LO;
key = key >> (32 - 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 uint32_t hash_code = GetPixPairHash64(argb);
p->chain_[pos] = p->hash_to_first_index_[hash_code];
p->hash_to_first_index_[hash_code] = pos;
}
// Returns the maximum number of hash chain lookups to do for a
// given compression quality. Return value in range [6, 86].
static int GetMaxItersForQuality(int quality, int low_effort) {
return (low_effort ? 6 : 8) + (quality * quality) / 128;
}
static int GetWindowSizeForHashChain(int quality, int xsize) {
const int max_window_size = (quality > 75) ? WINDOW_SIZE
: (quality > 50) ? (xsize << 8)
: (quality > 25) ? (xsize << 6)
: (xsize << 4);
assert(xsize > 0);
return (max_window_size > WINDOW_SIZE) ? WINDOW_SIZE : max_window_size;
}
static WEBP_INLINE int MaxFindCopyLength(int len) {
return (len < MAX_LENGTH) ? len : MAX_LENGTH;
}
static void HashChainFindOffset(const VP8LHashChain* const p, int base_position,
const uint32_t* const argb, int len,
int window_size, int* const distance_ptr) {
const uint32_t* const argb_start = argb + base_position;
const int min_pos =
(base_position > window_size) ? base_position - window_size : 0;
int pos;
assert(len <= MAX_LENGTH);
for (pos = p->hash_to_first_index_[GetPixPairHash64(argb_start)];
pos >= min_pos;
pos = p->chain_[pos]) {
const int curr_length =
FindMatchLength(argb + pos, argb_start, len - 1, len);
if (curr_length == len) break;
}
*distance_ptr = base_position - pos;
}
static int HashChainFindCopy(const VP8LHashChain* const p,
int base_position,
const uint32_t* const argb, int max_len,
int window_size, int iter_max,
int* const distance_ptr,
int* const length_ptr) {
const uint32_t* const argb_start = argb + base_position;
int iter = iter_max;
int best_length = 0;
int best_distance = 0;
const int min_pos =
(base_position > window_size) ? base_position - window_size : 0;
int pos;
int length_max = 256;
if (max_len < length_max) {
length_max = max_len;
}
for (pos = p->hash_to_first_index_[GetPixPairHash64(argb_start)];
pos >= min_pos;
pos = p->chain_[pos]) {
int curr_length;
int distance;
if (--iter < 0) {
break;
}
curr_length = FindMatchLength(argb + pos, argb_start, best_length, max_len);
if (best_length < curr_length) {
distance = base_position - pos;
best_length = curr_length;
best_distance = distance;
if (curr_length >= length_max) {
break;
}
}
}
*distance_ptr = best_distance;
*length_ptr = best_length;
return (best_length >= MIN_LENGTH);
}
static WEBP_INLINE void AddSingleLiteral(uint32_t pixel, int use_color_cache,
VP8LColorCache* const hashers,
VP8LBackwardRefs* const refs) {
PixOrCopy v;
if (use_color_cache) {
const uint32_t key = VP8LColorCacheGetIndex(hashers, pixel);
if (VP8LColorCacheLookup(hashers, key) == pixel) {
v = PixOrCopyCreateCacheIdx(key);
} else {
v = PixOrCopyCreateLiteral(pixel);
VP8LColorCacheSet(hashers, key, pixel);
}
} else {
v = PixOrCopyCreateLiteral(pixel);
}
BackwardRefsCursorAdd(refs, v);
}
static int BackwardReferencesRle(int xsize, int ysize,
const uint32_t* const argb,
int cache_bits, VP8LBackwardRefs* const refs) {
const int pix_count = xsize * ysize;
int i, k;
const int use_color_cache = (cache_bits > 0);
VP8LColorCache hashers;
if (use_color_cache && !VP8LColorCacheInit(&hashers, cache_bits)) {
return 0;
}
ClearBackwardRefs(refs);
// Add first pixel as literal.
AddSingleLiteral(argb[0], use_color_cache, &hashers, refs);
i = 1;
while (i < pix_count) {
const int max_len = MaxFindCopyLength(pix_count - i);
const int kMinLength = 4;
const int rle_len = FindMatchLength(argb + i, argb + i - 1, 0, max_len);
const int prev_row_len = (i < xsize) ? 0 :
FindMatchLength(argb + i, argb + i - xsize, 0, max_len);
if (rle_len >= prev_row_len && rle_len >= kMinLength) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(1, rle_len));
// We don't need to update the color cache here since it is always the
// same pixel being copied, and that does not change the color cache
// state.
i += rle_len;
} else if (prev_row_len >= kMinLength) {
BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(xsize, prev_row_len));
if (use_color_cache) {
for (k = 0; k < prev_row_len; ++k) {
VP8LColorCacheInsert(&hashers, argb[i + k]);
}
}
i += prev_row_len;
} else {
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
i++;
}
}
if (use_color_cache) VP8LColorCacheClear(&hashers);
return !refs->error_;
}
static int BackwardReferencesLz77(int xsize, int ysize,
const uint32_t* const argb, int cache_bits,
int quality, int low_effort,
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 iter_max = GetMaxItersForQuality(quality, low_effort);
const int window_size = GetWindowSizeForHashChain(quality, xsize);
int min_matches = 32;
if (use_color_cache) {
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) goto Error;
}
ClearBackwardRefs(refs);
HashChainReset(hash_chain);
for (i = 0; i < pix_count - 2; ) {
// Alternative#1: Code the pixels starting at 'i' using backward reference.
int offset = 0;
int len = 0;
const int max_len = MaxFindCopyLength(pix_count - i);
HashChainFindCopy(hash_chain, i, argb, max_len, window_size,
iter_max, &offset, &len);
if (len > MIN_LENGTH || (len == MIN_LENGTH && offset <= 512)) {
int offset2 = 0;
int len2 = 0;
int k;
min_matches = 8;
HashChainInsert(hash_chain, &argb[i], i);
if ((len < (max_len >> 2)) && !low_effort) {
// Evaluate Alternative#2: Insert the pixel at 'i' as literal, and code
// the pixels starting at 'i + 1' using backward reference.
HashChainFindCopy(hash_chain, i + 1, argb, max_len - 1,
window_size, iter_max, &offset2,
&len2);
if (len2 > len + 1) {
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
i++; // Backward reference to be done for next pixel.
len = len2;
offset = offset2;
}
}
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).
if (offset >= 3 && offset != xsize) {
const int last = (len < pix_count - 1 - i) ? len : pix_count - 1 - i;
for (k = 2; k < last - 8; k += 2) {
HashChainInsert(hash_chain, &argb[i + k], i + k);
}
for (; k < last; ++k) {
HashChainInsert(hash_chain, &argb[i + k], i + k);
}
}
i += len;
} else {
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
HashChainInsert(hash_chain, &argb[i], i);
++i;
--min_matches;
if (min_matches <= 0) {
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
HashChainInsert(hash_chain, &argb[i], i);
++i;
}
}
}
while (i < pix_count) {
// Handle the last pixel(s).
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
++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 blue_[VALUES_IN_BYTE];
double distance_[NUM_DISTANCE_CODES];
double* literal_;
} CostModel;
static int BackwardReferencesTraceBackwards(
int xsize, int ysize, 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 cache_bits,
VP8LBackwardRefs* const refs) {
int ok = 0;
VP8LHistogram* const 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 void AddSingleLiteralWithCostModel(
const uint32_t* const argb, VP8LHashChain* const hash_chain,
VP8LColorCache* const hashers, const CostModel* const cost_model, int idx,
int is_last, int use_color_cache, double prev_cost, float* const cost,
uint16_t* const dist_array) {
double cost_val = prev_cost;
const uint32_t color = argb[0];
if (!is_last) {
HashChainInsert(hash_chain, argb, idx);
}
if (use_color_cache && VP8LColorCacheContains(hashers, color)) {
const double mul0 = 0.68;
const int ix = VP8LColorCacheGetIndex(hashers, color);
cost_val += GetCacheCost(cost_model, ix) * mul0;
} else {
const double mul1 = 0.82;
if (use_color_cache) VP8LColorCacheInsert(hashers, color);
cost_val += GetLiteralCost(cost_model, color) * mul1;
}
if (cost[idx] > cost_val) {
cost[idx] = (float)cost_val;
dist_array[idx] = 1; // only one is inserted.
}
}
static int BackwardReferencesHashChainDistanceOnly(
int xsize, int ysize, const uint32_t* const argb,
int quality, int cache_bits, VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs, uint16_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));
const size_t literal_array_size = sizeof(double) *
(NUM_LITERAL_CODES + NUM_LENGTH_CODES +
((cache_bits > 0) ? (1 << cache_bits) : 0));
const size_t cost_model_size = sizeof(CostModel) + literal_array_size;
CostModel* const cost_model =
(CostModel*)WebPSafeMalloc(1ULL, cost_model_size);
VP8LColorCache hashers;
const int skip_length = 32 + quality;
const int skip_min_distance_code = 2;
int iter_max = GetMaxItersForQuality(quality, 0);
const int window_size = GetWindowSizeForHashChain(quality, xsize);
if (cost == NULL || cost_model == NULL) goto Error;
cost_model->literal_ = (double*)(cost_model + 1);
if (use_color_cache) {
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) goto Error;
}
if (!CostModelBuild(cost_model, cache_bits, 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;
HashChainReset(hash_chain);
// Add first pixel as literal.
AddSingleLiteralWithCostModel(argb + 0, hash_chain, &hashers, cost_model, 0,
0, use_color_cache, 0.0, cost, dist_array);
for (i = 1; i < pix_count - 1; ++i) {
int offset = 0;
int len = 0;
double prev_cost = cost[i - 1];
const int max_len = MaxFindCopyLength(pix_count - i);
HashChainFindCopy(hash_chain, i, argb, max_len, window_size,
iter_max, &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 >= skip_length && code <= skip_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 (len != MIN_LENGTH) {
int code_min_length;
double cost_total;
HashChainFindOffset(hash_chain, i, argb, MIN_LENGTH, window_size,
&offset);
code_min_length = DistanceToPlaneCode(xsize, offset);
cost_total = prev_cost +
GetDistanceCost(cost_model, code_min_length) +
GetLengthCost(cost_model, 1);
if (cost[i + 1] > cost_total) {
cost[i + 1] = (float)cost_total;
dist_array[i + 1] = 2;
}
}
}
AddSingleLiteralWithCostModel(argb + i, hash_chain, &hashers, cost_model, i,
0, use_color_cache, prev_cost, cost,
dist_array);
next_symbol: ;
}
// Handle the last pixel.
if (i == (pix_count - 1)) {
AddSingleLiteralWithCostModel(argb + i, hash_chain, &hashers, cost_model, i,
1, use_color_cache, cost[pix_count - 2], cost,
dist_array);
}
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(uint16_t* const dist_array,
int dist_array_size,
uint16_t** const chosen_path,
int* const chosen_path_size) {
uint16_t* path = dist_array + dist_array_size;
uint16_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 uint16_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 ix;
int i = 0;
int ok = 0;
int cc_init = 0;
const int window_size = GetWindowSizeForHashChain(quality, xsize);
VP8LColorCache hashers;
if (use_color_cache) {
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) goto Error;
}
ClearBackwardRefs(refs);
HashChainReset(hash_chain);
for (ix = 0; ix < chosen_path_size; ++ix) {
int offset = 0;
const int len = chosen_path[ix];
if (len != 1) {
int k;
HashChainFindOffset(hash_chain, i, argb, len, window_size, &offset);
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,
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;
uint16_t* chosen_path = NULL;
int chosen_path_size = 0;
uint16_t* dist_array =
(uint16_t*)WebPSafeMalloc(dist_array_size, sizeof(*dist_array));
if (dist_array == NULL) goto Error;
if (!BackwardReferencesHashChainDistanceOnly(
xsize, ysize, 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);
}
}
// Returns entropy for the given cache bits.
static double ComputeCacheEntropy(const uint32_t* argb,
const VP8LBackwardRefs* const refs,
int cache_bits) {
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;
}
if (!use_color_cache) {
while (VP8LRefsCursorOk(&c)) {
VP8LHistogramAddSinglePixOrCopy(histo, c.cur_pos);
VP8LRefsCursorNext(&c);
}
} else {
while (VP8LRefsCursorOk(&c)) {
const PixOrCopy* const v = c.cur_pos;
if (PixOrCopyIsLiteral(v)) {
const uint32_t pix = *argb++;
const uint32_t key = VP8LColorCacheGetIndex(&hashers, pix);
if (VP8LColorCacheLookup(&hashers, key) == pix) {
++histo->literal_[NUM_LITERAL_CODES + NUM_LENGTH_CODES + key];
} else {
VP8LColorCacheSet(&hashers, key, pix);
++histo->blue_[pix & 0xff];
++histo->literal_[(pix >> 8) & 0xff];
++histo->red_[(pix >> 16) & 0xff];
++histo->alpha_[pix >> 24];
}
} else {
int len = PixOrCopyLength(v);
int code, extra_bits;
VP8LPrefixEncodeBits(len, &code, &extra_bits);
++histo->literal_[NUM_LITERAL_CODES + code];
VP8LPrefixEncodeBits(PixOrCopyDistance(v), &code, &extra_bits);
++histo->distance_[code];
do {
VP8LColorCacheInsert(&hashers, *argb++);
} while(--len != 0);
}
VP8LRefsCursorNext(&c);
}
}
entropy = VP8LHistogramEstimateBits(histo) +
kSmallPenaltyForLargeCache * cache_bits;
Error:
if (cc_init) VP8LColorCacheClear(&hashers);
VP8LFreeHistogram(histo);
return entropy;
}
// Evaluate optimal cache bits for the local color cache.
// The input *best_cache_bits sets the maximum cache bits to use (passing 0
// implies disabling the local color cache). The local color cache is also
// disabled for the lower (<= 25) quality.
// Returns 0 in case of memory error.
static int CalculateBestCacheSize(const uint32_t* const argb,
int xsize, int ysize, int quality,
VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs,
int* const lz77_computed,
int* const best_cache_bits) {
int eval_low = 1;
int eval_high = 1;
double entropy_low = MAX_ENTROPY;
double entropy_high = MAX_ENTROPY;
const double cost_mul = 5e-4;
int cache_bits_low = 0;
int cache_bits_high = (quality <= 25) ? 0 : *best_cache_bits;
assert(cache_bits_high <= MAX_COLOR_CACHE_BITS);
*lz77_computed = 0;
if (cache_bits_high == 0) {
*best_cache_bits = 0;
// Local color cache is disabled.
return 1;
}
if (!BackwardReferencesLz77(xsize, ysize, argb, cache_bits_low, quality, 0,
hash_chain, refs)) {
return 0;
}
// Do a binary search to find the optimal entropy for cache_bits.
while (eval_low || eval_high) {
if (eval_low) {
entropy_low = ComputeCacheEntropy(argb, refs, cache_bits_low);
entropy_low += entropy_low * cache_bits_low * cost_mul;
eval_low = 0;
}
if (eval_high) {
entropy_high = ComputeCacheEntropy(argb, refs, cache_bits_high);
entropy_high += entropy_high * cache_bits_high * cost_mul;
eval_high = 0;
}
if (entropy_high < entropy_low) {
const int prev_cache_bits_low = cache_bits_low;
*best_cache_bits = cache_bits_high;
cache_bits_low = (cache_bits_low + cache_bits_high) / 2;
if (cache_bits_low != prev_cache_bits_low) eval_low = 1;
} else {
*best_cache_bits = cache_bits_low;
cache_bits_high = (cache_bits_low + cache_bits_high) / 2;
if (cache_bits_high != cache_bits_low) eval_high = 1;
}
}
*lz77_computed = 1;
return 1;
}
// Update (in-place) backward references for specified cache_bits.
static int BackwardRefsWithLocalCache(const uint32_t* const argb,
int cache_bits,
VP8LBackwardRefs* const refs) {
int pixel_index = 0;
VP8LColorCache hashers;
VP8LRefsCursor c = VP8LRefsCursorInit(refs);
if (!VP8LColorCacheInit(&hashers, cache_bits)) return 0;
while (VP8LRefsCursorOk(&c)) {
PixOrCopy* const v = c.cur_pos;
if (PixOrCopyIsLiteral(v)) {
const uint32_t argb_literal = v->argb_or_distance;
if (VP8LColorCacheContains(&hashers, argb_literal)) {
const int ix = VP8LColorCacheGetIndex(&hashers, argb_literal);
*v = PixOrCopyCreateCacheIdx(ix);
} else {
VP8LColorCacheInsert(&hashers, argb_literal);
}
++pixel_index;
} else {
// refs was created without local cache, so it can not have cache indexes.
int k;
assert(PixOrCopyIsCopy(v));
for (k = 0; k < v->len; ++k) {
VP8LColorCacheInsert(&hashers, argb[pixel_index++]);
}
}
VP8LRefsCursorNext(&c);
}
VP8LColorCacheClear(&hashers);
return 1;
}
static VP8LBackwardRefs* GetBackwardReferencesLowEffort(
int width, int height, const uint32_t* const argb, int quality,
int* const cache_bits, VP8LHashChain* const hash_chain,
VP8LBackwardRefs refs_array[2]) {
VP8LBackwardRefs* refs_lz77 = &refs_array[0];
*cache_bits = 0;
if (!BackwardReferencesLz77(width, height, argb, 0, quality,
1 /* Low effort. */, hash_chain, refs_lz77)) {
return NULL;
}
BackwardReferences2DLocality(width, refs_lz77);
return refs_lz77;
}
static VP8LBackwardRefs* GetBackwardReferences(
int width, int height, const uint32_t* const argb, int quality,
int* const cache_bits, VP8LHashChain* const hash_chain,
VP8LBackwardRefs refs_array[2]) {
int lz77_is_useful;
int lz77_computed;
double bit_cost_lz77, bit_cost_rle;
VP8LBackwardRefs* best = NULL;
VP8LBackwardRefs* refs_lz77 = &refs_array[0];
VP8LBackwardRefs* refs_rle = &refs_array[1];
VP8LHistogram* histo = NULL;
if (!CalculateBestCacheSize(argb, width, height, quality, hash_chain,
refs_lz77, &lz77_computed, cache_bits)) {
goto Error;
}
if (lz77_computed) {
// Transform refs_lz77 for the optimized cache_bits.
if (*cache_bits > 0) {
if (!BackwardRefsWithLocalCache(argb, *cache_bits, refs_lz77)) {
goto Error;
}
}
} else {
if (!BackwardReferencesLz77(width, height, argb, *cache_bits, quality,
0 /* Low effort. */, hash_chain, refs_lz77)) {
goto Error;
}
}
if (!BackwardReferencesRle(width, height, argb, *cache_bits, refs_rle)) {
goto Error;
}
histo = VP8LAllocateHistogram(*cache_bits);
if (histo == NULL) goto Error;
{
// 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);
}
// 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) {
VP8LBackwardRefs* const refs_trace = refs_rle;
if (!VP8LBackwardRefsCopy(refs_lz77, refs_trace)) {
best = NULL;
goto Error;
}
if (BackwardReferencesTraceBackwards(width, height, argb, quality,
*cache_bits, hash_chain,
refs_trace)) {
double bit_cost_trace;
// Evaluate LZ77 coding.
VP8LHistogramCreate(histo, refs_trace, *cache_bits);
bit_cost_trace = VP8LHistogramEstimateBits(histo);
if (bit_cost_trace < bit_cost_lz77) {
best = refs_trace;
}
}
}
} else {
best = refs_rle;
}
BackwardReferences2DLocality(width, best);
Error:
VP8LFreeHistogram(histo);
return best;
}
VP8LBackwardRefs* VP8LGetBackwardReferences(
int width, int height, const uint32_t* const argb, int quality,
int low_effort, int* const cache_bits, VP8LHashChain* const hash_chain,
VP8LBackwardRefs refs_array[2]) {
if (low_effort) {
return GetBackwardReferencesLowEffort(width, height, argb, quality,
cache_bits, hash_chain, refs_array);
} else {
return GetBackwardReferences(width, height, argb, quality, cache_bits,
hash_chain, refs_array);
}
}