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Unified Diff: third_party/libwebp/enc/backward_references.c

Issue 1178013008: Use the upstream version of libwebp, v0.4.3. (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: Fixes for SkWebpImageDecoder and SkWebpCodec. Created 5 years, 6 months ago
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Index: third_party/libwebp/enc/backward_references.c
diff --git a/third_party/libwebp/enc/backward_references.c b/third_party/libwebp/enc/backward_references.c
new file mode 100644
index 0000000000000000000000000000000000000000..a3c30aa0710e327eebe2234c25d3d6bb5ddba4a7
--- /dev/null
+++ b/third_party/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;
+}
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