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godot/drivers/webp/enc/backward_references.c

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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 <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 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 HashChain* 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 uint64_t* const ptr1 =
(const uint64_t*)(argb + pos + best_length - 1);
const uint64_t* const ptr2 =
(const uint64_t*)(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 != *ptr2) 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) {
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;
int window_size = WINDOW_SIZE;
int iter_pos = 1;
int iter_limit = -1;
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;
GetParamsForHashChainFindCopy(quality, xsize, cache_bits,
&window_size, &iter_pos, &iter_limit);
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.
if (use_color_cache && VP8LColorCacheContains(&hashers, pixel)) {
const int ix = VP8LColorCacheGetIndex(&hashers, pixel);
refs->refs[refs->size] = PixOrCopyCreateCacheIdx(ix);
} else {
if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
refs->refs[refs->size] = PixOrCopyCreateLiteral(pixel);
}
++refs->size;
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 {
if (use_color_cache) VP8LColorCacheInsert(&hashers, pixel);
refs->refs[refs->size] = PixOrCopyCreateLiteral(pixel);
}
++refs->size;
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 quality, 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 quality, int cache_bits) {
int ok = 0;
VP8LHistogram histo;
VP8LBackwardRefs refs;
if (!VP8LBackwardRefsAlloc(&refs, xsize * ysize)) goto Error;
if (recursion_level > 0) {
if (!BackwardReferencesTraceBackwards(xsize, ysize, recursion_level - 1,
argb, quality, 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;
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, 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((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;
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 || 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,
quality, cache_bits)) {
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);
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 = 1;
Error:
if (cc_init) VP8LColorCacheClear(&hashers);
HashChainDelete(hash_chain);
free(cost_model);
free(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,
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;
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;
GetParamsForHashChainFindCopy(quality, xsize, cache_bits,
&window_size, &iter_pos, &iter_limit);
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);
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 {
if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
refs->refs[size] = PixOrCopyCreateLiteral(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 quality, 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, quality, cache_bits,
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,
refs)) {
goto Error;
}
ok = 1;
Error:
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. Don't execute it at lower quality.
const int try_lz77_trace_backwards = (quality >= 25);
*best = refs_lz77; // default guess: lz77 is better
VP8LClearBackwardRefs(&refs_rle);
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 refs_trace;
if (!VP8LBackwardRefsAlloc(&refs_trace, num_pix)) {
goto End;
}
if (BackwardReferencesTraceBackwards(width, height, recursion_level, argb,
quality, 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;
}
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