// 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 #include #include "src/enc/backward_references_enc.h" #include "src/enc/histogram_enc.h" #include "src/dsp/lossless.h" #include "src/dsp/lossless_common.h" #include "src/dsp/dsp.h" #include "src/utils/color_cache_utils.h" #include "src/utils/utils.h" #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 << WINDOW_SIZE_BITS) - 120) // Minimum number of pixels for which it is cheaper to encode a // distance + length instead of each pixel as a literal. #define MIN_LENGTH 4 // ----------------------------------------------------------------------------- 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 }; extern int VP8LDistanceToPlaneCode(int xsize, int dist); int VP8LDistanceToPlaneCode(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. For an index // inferior or equal to best_len_match, the return value just has to be strictly // inferior to best_len_match. The current behavior is to return 0 if this index // is best_len_match, and the index itself otherwise. // 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) { // 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; return VP8LVectorMismatch(array1, array2, max_limit); } // ----------------------------------------------------------------------------- // VP8LBackwardRefs struct PixOrCopyBlock { PixOrCopyBlock* next_; // next block (or NULL) PixOrCopy* start_; // data start int size_; // currently used size }; extern void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs); void VP8LClearBackwardRefs(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); VP8LClearBackwardRefs(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; } extern void VP8LBackwardRefsCursorAdd(VP8LBackwardRefs* const refs, const PixOrCopy v); void VP8LBackwardRefsCursorAdd(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; } // ----------------------------------------------------------------------------- // Hash chains int VP8LHashChainInit(VP8LHashChain* const p, int size) { assert(p->size_ == 0); assert(p->offset_length_ == NULL); assert(size > 0); p->offset_length_ = (uint32_t*)WebPSafeMalloc(size, sizeof(*p->offset_length_)); if (p->offset_length_ == NULL) return 0; p->size_ = size; return 1; } void VP8LHashChainClear(VP8LHashChain* const p) { assert(p != NULL); WebPSafeFree(p->offset_length_); p->size_ = 0; p->offset_length_ = NULL; } // ----------------------------------------------------------------------------- #define HASH_MULTIPLIER_HI (0xc6a4a793ULL) #define HASH_MULTIPLIER_LO (0x5bd1e996ULL) static WEBP_INLINE uint32_t GetPixPairHash64(const uint32_t* const argb) { uint32_t key; key = (argb[1] * HASH_MULTIPLIER_HI) & 0xffffffffu; key += (argb[0] * HASH_MULTIPLIER_LO) & 0xffffffffu; key = key >> (32 - HASH_BITS); return key; } // Returns the maximum number of hash chain lookups to do for a // given compression quality. Return value in range [8, 86]. static int GetMaxItersForQuality(int quality) { return 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; } int VP8LHashChainFill(VP8LHashChain* const p, int quality, const uint32_t* const argb, int xsize, int ysize, int low_effort) { const int size = xsize * ysize; const int iter_max = GetMaxItersForQuality(quality); const uint32_t window_size = GetWindowSizeForHashChain(quality, xsize); int pos; int argb_comp; uint32_t base_position; int32_t* hash_to_first_index; // Temporarily use the p->offset_length_ as a hash chain. int32_t* chain = (int32_t*)p->offset_length_; assert(size > 0); assert(p->size_ != 0); assert(p->offset_length_ != NULL); if (size <= 2) { p->offset_length_[0] = p->offset_length_[size - 1] = 0; return 1; } hash_to_first_index = (int32_t*)WebPSafeMalloc(HASH_SIZE, sizeof(*hash_to_first_index)); if (hash_to_first_index == NULL) return 0; // Set the int32_t array to -1. memset(hash_to_first_index, 0xff, HASH_SIZE * sizeof(*hash_to_first_index)); // Fill the chain linking pixels with the same hash. argb_comp = (argb[0] == argb[1]); for (pos = 0; pos < size - 2;) { uint32_t hash_code; const int argb_comp_next = (argb[pos + 1] == argb[pos + 2]); if (argb_comp && argb_comp_next) { // Consecutive pixels with the same color will share the same hash. // We therefore use a different hash: the color and its repetition // length. uint32_t tmp[2]; uint32_t len = 1; tmp[0] = argb[pos]; // Figure out how far the pixels are the same. // The last pixel has a different 64 bit hash, as its next pixel does // not have the same color, so we just need to get to the last pixel equal // to its follower. while (pos + (int)len + 2 < size && argb[pos + len + 2] == argb[pos]) { ++len; } if (len > MAX_LENGTH) { // Skip the pixels that match for distance=1 and length>MAX_LENGTH // because they are linked to their predecessor and we automatically // check that in the main for loop below. Skipping means setting no // predecessor in the chain, hence -1. memset(chain + pos, 0xff, (len - MAX_LENGTH) * sizeof(*chain)); pos += len - MAX_LENGTH; len = MAX_LENGTH; } // Process the rest of the hash chain. while (len) { tmp[1] = len--; hash_code = GetPixPairHash64(tmp); chain[pos] = hash_to_first_index[hash_code]; hash_to_first_index[hash_code] = pos++; } argb_comp = 0; } else { // Just move one pixel forward. hash_code = GetPixPairHash64(argb + pos); chain[pos] = hash_to_first_index[hash_code]; hash_to_first_index[hash_code] = pos++; argb_comp = argb_comp_next; } } // Process the penultimate pixel. chain[pos] = hash_to_first_index[GetPixPairHash64(argb + pos)]; WebPSafeFree(hash_to_first_index); // Find the best match interval at each pixel, defined by an offset to the // pixel and a length. The right-most pixel cannot match anything to the right // (hence a best length of 0) and the left-most pixel nothing to the left // (hence an offset of 0). assert(size > 2); p->offset_length_[0] = p->offset_length_[size - 1] = 0; for (base_position = size - 2; base_position > 0;) { const int max_len = MaxFindCopyLength(size - 1 - base_position); const uint32_t* const argb_start = argb + base_position; int iter = iter_max; int best_length = 0; uint32_t best_distance = 0; uint32_t best_argb; const int min_pos = (base_position > window_size) ? base_position - window_size : 0; const int length_max = (max_len < 256) ? max_len : 256; uint32_t max_base_position; pos = chain[base_position]; if (!low_effort) { int curr_length; // Heuristic: use the comparison with the above line as an initialization. if (base_position >= (uint32_t)xsize) { curr_length = FindMatchLength(argb_start - xsize, argb_start, best_length, max_len); if (curr_length > best_length) { best_length = curr_length; best_distance = xsize; } --iter; } // Heuristic: compare to the previous pixel. curr_length = FindMatchLength(argb_start - 1, argb_start, best_length, max_len); if (curr_length > best_length) { best_length = curr_length; best_distance = 1; } --iter; // Skip the for loop if we already have the maximum. if (best_length == MAX_LENGTH) pos = min_pos - 1; } best_argb = argb_start[best_length]; for (; pos >= min_pos && --iter; pos = chain[pos]) { int curr_length; assert(base_position > (uint32_t)pos); if (argb[pos + best_length] != best_argb) continue; curr_length = VP8LVectorMismatch(argb + pos, argb_start, max_len); if (best_length < curr_length) { best_length = curr_length; best_distance = base_position - pos; best_argb = argb_start[best_length]; // Stop if we have reached a good enough length. if (best_length >= length_max) break; } } // We have the best match but in case the two intervals continue matching // to the left, we have the best matches for the left-extended pixels. max_base_position = base_position; while (1) { assert(best_length <= MAX_LENGTH); assert(best_distance <= WINDOW_SIZE); p->offset_length_[base_position] = (best_distance << MAX_LENGTH_BITS) | (uint32_t)best_length; --base_position; // Stop if we don't have a match or if we are out of bounds. if (best_distance == 0 || base_position == 0) break; // Stop if we cannot extend the matching intervals to the left. if (base_position < best_distance || argb[base_position - best_distance] != argb[base_position]) { break; } // Stop if we are matching at its limit because there could be a closer // matching interval with the same maximum length. Then again, if the // matching interval is as close as possible (best_distance == 1), we will // never find anything better so let's continue. if (best_length == MAX_LENGTH && best_distance != 1 && base_position + MAX_LENGTH < max_base_position) { break; } if (best_length < MAX_LENGTH) { ++best_length; max_base_position = base_position; } } } return 1; } 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); } VP8LBackwardRefsCursorAdd(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; } VP8LClearBackwardRefs(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 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 >= MIN_LENGTH) { VP8LBackwardRefsCursorAdd(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 >= MIN_LENGTH) { VP8LBackwardRefsCursorAdd(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, const VP8LHashChain* const hash_chain, VP8LBackwardRefs* const refs) { int i; int i_last_check = -1; int ok = 0; int cc_init = 0; const int use_color_cache = (cache_bits > 0); const int pix_count = xsize * ysize; VP8LColorCache hashers; if (use_color_cache) { cc_init = VP8LColorCacheInit(&hashers, cache_bits); if (!cc_init) goto Error; } VP8LClearBackwardRefs(refs); for (i = 0; i < pix_count;) { // Alternative#1: Code the pixels starting at 'i' using backward reference. int offset = 0; int len = 0; int j; VP8LHashChainFindCopy(hash_chain, i, &offset, &len); if (len >= MIN_LENGTH) { const int len_ini = len; int max_reach = 0; const int j_max = (i + len_ini >= pix_count) ? pix_count - 1 : i + len_ini; // Only start from what we have not checked already. i_last_check = (i > i_last_check) ? i : i_last_check; // We know the best match for the current pixel but we try to find the // best matches for the current pixel AND the next one combined. // The naive method would use the intervals: // [i,i+len) + [i+len, length of best match at i+len) // while we check if we can use: // [i,j) (where j<=i+len) + [j, length of best match at j) for (j = i_last_check + 1; j <= j_max; ++j) { const int len_j = VP8LHashChainFindLength(hash_chain, j); const int reach = j + (len_j >= MIN_LENGTH ? len_j : 1); // 1 for single literal. if (reach > max_reach) { len = j - i; max_reach = reach; if (max_reach >= pix_count) break; } } } else { len = 1; } // Go with literal or backward reference. assert(len > 0); if (len == 1) { AddSingleLiteral(argb[i], use_color_cache, &hashers, refs); } else { VP8LBackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(offset, len)); if (use_color_cache) { for (j = i; j < i + len; ++j) VP8LColorCacheInsert(&hashers, argb[j]); } } i += len; } ok = !refs->error_; Error: if (cc_init) VP8LColorCacheClear(&hashers); return ok; } // Compute an LZ77 by forcing matches to happen within a given distance cost. // We therefore limit the algorithm to the lowest 32 values in the PlaneCode // definition. #define WINDOW_OFFSETS_SIZE_MAX 32 static int BackwardReferencesLz77Box(int xsize, int ysize, const uint32_t* const argb, int cache_bits, const VP8LHashChain* const hash_chain_best, VP8LHashChain* hash_chain, VP8LBackwardRefs* const refs) { int i; const int pix_count = xsize * ysize; uint16_t* counts; int window_offsets[WINDOW_OFFSETS_SIZE_MAX] = {0}; int window_offsets_new[WINDOW_OFFSETS_SIZE_MAX] = {0}; int window_offsets_size = 0; int window_offsets_new_size = 0; uint16_t* const counts_ini = (uint16_t*)WebPSafeMalloc(xsize * ysize, sizeof(*counts_ini)); int best_offset_prev = -1, best_length_prev = -1; if (counts_ini == NULL) return 0; // counts[i] counts how many times a pixel is repeated starting at position i. i = pix_count - 2; counts = counts_ini + i; counts[1] = 1; for (; i >= 0; --i, --counts) { if (argb[i] == argb[i + 1]) { // Max out the counts to MAX_LENGTH. counts[0] = counts[1] + (counts[1] != MAX_LENGTH); } else { counts[0] = 1; } } // Figure out the window offsets around a pixel. They are stored in a // spiraling order around the pixel as defined by VP8LDistanceToPlaneCode. { int x, y; for (y = 0; y <= 6; ++y) { for (x = -6; x <= 6; ++x) { const int offset = y * xsize + x; int plane_code; // Ignore offsets that bring us after the pixel. if (offset <= 0) continue; plane_code = VP8LDistanceToPlaneCode(xsize, offset) - 1; if (plane_code >= WINDOW_OFFSETS_SIZE_MAX) continue; window_offsets[plane_code] = offset; } } // For narrow images, not all plane codes are reached, so remove those. for (i = 0; i < WINDOW_OFFSETS_SIZE_MAX; ++i) { if (window_offsets[i] == 0) continue; window_offsets[window_offsets_size++] = window_offsets[i]; } // Given a pixel P, find the offsets that reach pixels unreachable from P-1 // with any of the offsets in window_offsets[]. for (i = 0; i < window_offsets_size; ++i) { int j; int is_reachable = 0; for (j = 0; j < window_offsets_size && !is_reachable; ++j) { is_reachable |= (window_offsets[i] == window_offsets[j] + 1); } if (!is_reachable) { window_offsets_new[window_offsets_new_size] = window_offsets[i]; ++window_offsets_new_size; } } } hash_chain->offset_length_[0] = 0; for (i = 1; i < pix_count; ++i) { int ind; int best_length = VP8LHashChainFindLength(hash_chain_best, i); int best_offset; int do_compute = 1; if (best_length >= MAX_LENGTH) { // Do not recompute the best match if we already have a maximal one in the // window. best_offset = VP8LHashChainFindOffset(hash_chain_best, i); for (ind = 0; ind < window_offsets_size; ++ind) { if (best_offset == window_offsets[ind]) { do_compute = 0; break; } } } if (do_compute) { // Figure out if we should use the offset/length from the previous pixel // as an initial guess and therefore only inspect the offsets in // window_offsets_new[]. const int use_prev = (best_length_prev > 1) && (best_length_prev < MAX_LENGTH); const int num_ind = use_prev ? window_offsets_new_size : window_offsets_size; best_length = use_prev ? best_length_prev - 1 : 0; best_offset = use_prev ? best_offset_prev : 0; // Find the longest match in a window around the pixel. for (ind = 0; ind < num_ind; ++ind) { int curr_length = 0; int j = i; int j_offset = use_prev ? i - window_offsets_new[ind] : i - window_offsets[ind]; if (j_offset < 0 || argb[j_offset] != argb[i]) continue; // The longest match is the sum of how many times each pixel is // repeated. do { const int counts_j_offset = counts_ini[j_offset]; const int counts_j = counts_ini[j]; if (counts_j_offset != counts_j) { curr_length += (counts_j_offset < counts_j) ? counts_j_offset : counts_j; break; } // The same color is repeated counts_pos times at j_offset and j. curr_length += counts_j_offset; j_offset += counts_j_offset; j += counts_j_offset; } while (curr_length <= MAX_LENGTH && j < pix_count && argb[j_offset] == argb[j]); if (best_length < curr_length) { best_offset = use_prev ? window_offsets_new[ind] : window_offsets[ind]; if (curr_length >= MAX_LENGTH) { best_length = MAX_LENGTH; break; } else { best_length = curr_length; } } } } assert(i + best_length <= pix_count); assert(best_length <= MAX_LENGTH); if (best_length <= MIN_LENGTH) { hash_chain->offset_length_[i] = 0; best_offset_prev = 0; best_length_prev = 0; } else { hash_chain->offset_length_[i] = (best_offset << MAX_LENGTH_BITS) | (uint32_t)best_length; best_offset_prev = best_offset; best_length_prev = best_length; } } hash_chain->offset_length_[0] = 0; WebPSafeFree(counts_ini); return BackwardReferencesLz77(xsize, ysize, argb, cache_bits, hash_chain, refs); } // ----------------------------------------------------------------------------- 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 = VP8LDistanceToPlaneCode(xsize, dist); c.cur_pos->argb_or_distance = transformed_dist; } VP8LRefsCursorNext(&c); } } // 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* argb, int quality, const VP8LBackwardRefs* const refs, int* const best_cache_bits) { int i; const int cache_bits_max = (quality <= 25) ? 0 : *best_cache_bits; double entropy_min = MAX_ENTROPY; int cc_init[MAX_COLOR_CACHE_BITS + 1] = { 0 }; VP8LColorCache hashers[MAX_COLOR_CACHE_BITS + 1]; VP8LRefsCursor c = VP8LRefsCursorInit(refs); VP8LHistogram* histos[MAX_COLOR_CACHE_BITS + 1] = { NULL }; int ok = 0; assert(cache_bits_max >= 0 && cache_bits_max <= MAX_COLOR_CACHE_BITS); if (cache_bits_max == 0) { *best_cache_bits = 0; // Local color cache is disabled. return 1; } // Allocate data. for (i = 0; i <= cache_bits_max; ++i) { histos[i] = VP8LAllocateHistogram(i); if (histos[i] == NULL) goto Error; if (i == 0) continue; cc_init[i] = VP8LColorCacheInit(&hashers[i], i); if (!cc_init[i]) goto Error; } // Find the cache_bits giving the lowest entropy. The search is done in a // brute-force way as the function (entropy w.r.t cache_bits) can be // anything in practice. while (VP8LRefsCursorOk(&c)) { const PixOrCopy* const v = c.cur_pos; if (PixOrCopyIsLiteral(v)) { const uint32_t pix = *argb++; const uint32_t a = (pix >> 24) & 0xff; const uint32_t r = (pix >> 16) & 0xff; const uint32_t g = (pix >> 8) & 0xff; const uint32_t b = (pix >> 0) & 0xff; // The keys of the caches can be derived from the longest one. int key = VP8LHashPix(pix, 32 - cache_bits_max); // Do not use the color cache for cache_bits = 0. ++histos[0]->blue_[b]; ++histos[0]->literal_[g]; ++histos[0]->red_[r]; ++histos[0]->alpha_[a]; // Deal with cache_bits > 0. for (i = cache_bits_max; i >= 1; --i, key >>= 1) { if (VP8LColorCacheLookup(&hashers[i], key) == pix) { ++histos[i]->literal_[NUM_LITERAL_CODES + NUM_LENGTH_CODES + key]; } else { VP8LColorCacheSet(&hashers[i], key, pix); ++histos[i]->blue_[b]; ++histos[i]->literal_[g]; ++histos[i]->red_[r]; ++histos[i]->alpha_[a]; } } } else { // We should compute the contribution of the (distance,length) // histograms but those are the same independently from the cache size. // As those constant contributions are in the end added to the other // histogram contributions, we can safely ignore them. int len = PixOrCopyLength(v); uint32_t argb_prev = *argb ^ 0xffffffffu; // Update the color caches. do { if (*argb != argb_prev) { // Efficiency: insert only if the color changes. int key = VP8LHashPix(*argb, 32 - cache_bits_max); for (i = cache_bits_max; i >= 1; --i, key >>= 1) { hashers[i].colors_[key] = *argb; } argb_prev = *argb; } argb++; } while (--len != 0); } VP8LRefsCursorNext(&c); } for (i = 0; i <= cache_bits_max; ++i) { const double entropy = VP8LHistogramEstimateBits(histos[i]); if (i == 0 || entropy < entropy_min) { entropy_min = entropy; *best_cache_bits = i; } } ok = 1; Error: for (i = 0; i <= cache_bits_max; ++i) { if (cc_init[i]) VP8LColorCacheClear(&hashers[i]); VP8LFreeHistogram(histos[i]); } return ok; } // 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; const int ix = VP8LColorCacheContains(&hashers, argb_literal); if (ix >= 0) { // hashers contains 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* const cache_bits, const VP8LHashChain* const hash_chain, VP8LBackwardRefs* const refs_lz77) { *cache_bits = 0; if (!BackwardReferencesLz77(width, height, argb, 0, hash_chain, refs_lz77)) { return NULL; } BackwardReferences2DLocality(width, refs_lz77); return refs_lz77; } extern int VP8LBackwardReferencesTraceBackwards( int xsize, int ysize, const uint32_t* const argb, int cache_bits, const VP8LHashChain* const hash_chain, const VP8LBackwardRefs* const refs_src, VP8LBackwardRefs* const refs_dst); static VP8LBackwardRefs* GetBackwardReferences( int width, int height, const uint32_t* const argb, int quality, int lz77_types_to_try, int* const cache_bits, const VP8LHashChain* const hash_chain, VP8LBackwardRefs* best, VP8LBackwardRefs* worst) { const int cache_bits_initial = *cache_bits; double bit_cost_best = -1; VP8LHistogram* histo = NULL; int lz77_type, lz77_type_best = 0; VP8LHashChain hash_chain_box; memset(&hash_chain_box, 0, sizeof(hash_chain_box)); histo = VP8LAllocateHistogram(MAX_COLOR_CACHE_BITS); if (histo == NULL) goto Error; for (lz77_type = 1; lz77_types_to_try; lz77_types_to_try &= ~lz77_type, lz77_type <<= 1) { int res = 0; double bit_cost; int cache_bits_tmp = cache_bits_initial; if ((lz77_types_to_try & lz77_type) == 0) continue; switch (lz77_type) { case kLZ77RLE: res = BackwardReferencesRle(width, height, argb, 0, worst); break; case kLZ77Standard: // Compute LZ77 with no cache (0 bits), as the ideal LZ77 with a color // cache is not that different in practice. res = BackwardReferencesLz77(width, height, argb, 0, hash_chain, worst); break; case kLZ77Box: if (!VP8LHashChainInit(&hash_chain_box, width * height)) goto Error; res = BackwardReferencesLz77Box(width, height, argb, 0, hash_chain, &hash_chain_box, worst); break; default: assert(0); } if (!res) goto Error; // Next, try with a color cache and update the references. if (!CalculateBestCacheSize(argb, quality, worst, &cache_bits_tmp)) { goto Error; } if (cache_bits_tmp > 0) { if (!BackwardRefsWithLocalCache(argb, cache_bits_tmp, worst)) { goto Error; } } // Keep the best backward references. VP8LHistogramCreate(histo, worst, cache_bits_tmp); bit_cost = VP8LHistogramEstimateBits(histo); if (lz77_type_best == 0 || bit_cost < bit_cost_best) { VP8LBackwardRefs* const tmp = worst; worst = best; best = tmp; bit_cost_best = bit_cost; *cache_bits = cache_bits_tmp; lz77_type_best = lz77_type; } } assert(lz77_type_best > 0); // Improve on simple LZ77 but only for high quality (TraceBackwards is // costly). if ((lz77_type_best == kLZ77Standard || lz77_type_best == kLZ77Box) && quality >= 25) { const VP8LHashChain* const hash_chain_tmp = (lz77_type_best == kLZ77Standard) ? hash_chain : &hash_chain_box; if (VP8LBackwardReferencesTraceBackwards(width, height, argb, *cache_bits, hash_chain_tmp, best, worst)) { double bit_cost_trace; VP8LHistogramCreate(histo, worst, *cache_bits); bit_cost_trace = VP8LHistogramEstimateBits(histo); if (bit_cost_trace < bit_cost_best) best = worst; } } BackwardReferences2DLocality(width, best); Error: VP8LHashChainClear(&hash_chain_box); VP8LFreeHistogram(histo); return best; } VP8LBackwardRefs* VP8LGetBackwardReferences( int width, int height, const uint32_t* const argb, int quality, int low_effort, int lz77_types_to_try, int* const cache_bits, const VP8LHashChain* const hash_chain, VP8LBackwardRefs* const refs_tmp1, VP8LBackwardRefs* const refs_tmp2) { if (low_effort) { return GetBackwardReferencesLowEffort(width, height, argb, cache_bits, hash_chain, refs_tmp1); } else { return GetBackwardReferences(width, height, argb, quality, lz77_types_to_try, cache_bits, hash_chain, refs_tmp1, refs_tmp2); } }