diff options
Diffstat (limited to 'src/main/jni/libwebp/enc/backward_references.c')
| -rw-r--r-- | src/main/jni/libwebp/enc/backward_references.c | 975 |
1 files changed, 975 insertions, 0 deletions
diff --git a/src/main/jni/libwebp/enc/backward_references.c b/src/main/jni/libwebp/enc/backward_references.c new file mode 100644 index 000000000..a3c30aa07 --- /dev/null +++ b/src/main/jni/libwebp/enc/backward_references.c @@ -0,0 +1,975 @@ +// 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; +} |