From 4167a3f5f758df0809e313d11073fb3d8ef7f6e1 Mon Sep 17 00:00:00 2001 From: Vikas Arora Date: Fri, 31 Oct 2014 18:07:11 -0700 Subject: [PATCH] Optimize backwardreferences Optimize backwardreferences (about 0.1% byte savings) with almost same compression speed (3% faster on defaut compression settings). 1.) Simplified iteration logic for HashChainFindCopy. - Remapped the iter_max constant. 2.) Simplified main for loop for BackwardReferencesHashChain - Removed 'if' conditions for corner cases in the main loop. - Refactored the method(AddSingleLiteral) for adding one pixel. Change-Id: I1bc44832fd81f11e714868a13e606c8f83157e64 --- src/enc/backward_references.c | 185 ++++++++++++++++------------------ 1 file changed, 85 insertions(+), 100 deletions(-) diff --git a/src/enc/backward_references.c b/src/enc/backward_references.c index 7d7e9a9f..e235986b 100644 --- a/src/enc/backward_references.c +++ b/src/enc/backward_references.c @@ -227,22 +227,23 @@ static void HashChainInsert(VP8LHashChain* const p, 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) +static void GetParamsForHashChainFindCopy( + int quality, int* iter_max, int* len_for_unit_dist) { + *iter_max = 8 + (quality * quality) / 40; + *len_for_unit_dist = 32 + (96 * quality) / 100; +} + +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); - *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; + return (max_window_size > WINDOW_SIZE) ? WINDOW_SIZE : max_window_size; +} + +static WEBP_INLINE int MaxFindCopyLength(int len) { + return (len < MAX_LENGTH) ? len : MAX_LENGTH; } static void HashChainFindOffset(const VP8LHashChain* const p, int base_position, @@ -266,30 +267,30 @@ static void HashChainFindOffset(const VP8LHashChain* const p, int base_position, static int HashChainFindCopy(const VP8LHashChain* const p, int base_position, int xsize, const uint32_t* const argb, int max_len, - int window_size, int iter_pos, int iter_limit, + int window_size, int iter_max, + int len_for_unit_dist, int* const distance_ptr, int* const length_ptr) { const uint32_t* const argb_start = argb + base_position; + int iter = 0; int best_length = 1; + const int length_max = 256; int best_distance = 0; 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]) { int curr_length; int distance; - if (iter_pos < 0) { - if (iter_pos < iter_limit || best_length >= 255) { + if (iter > 8) { + if (iter > iter_max || best_length >= length_max) { break; } } - --iter_pos; + ++iter; curr_length = FindMatchLength(argb + pos, argb_start, best_length, max_len); if (curr_length < best_length) continue; @@ -301,8 +302,8 @@ static int HashChainFindCopy(const VP8LHashChain* const p, if (curr_length >= max_len) { break; } - if ((best_distance == 1 || distance == xsize) && - best_length >= 128) { + if ((distance == 1 || distance == xsize) && + best_length >= len_for_unit_dist) { break; } } @@ -344,6 +345,21 @@ static int BackwardReferencesRle(int xsize, int ysize, return !refs->error_; } +static void AddSingleLiteral(uint32_t pixel, int use_color_cache, + VP8LColorCache* const hashers, + VP8LBackwardRefs* const refs) { + 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); +} + static int BackwardReferencesHashChain(int xsize, int ysize, const uint32_t* const argb, int cache_bits, int quality, @@ -355,61 +371,41 @@ static int BackwardReferencesHashChain(int xsize, int ysize, 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; + int iter_max, len_for_unit_dist; + const int window_size = GetWindowSizeForHashChain(quality, xsize); + GetParamsForHashChainFindCopy(quality, &iter_max, &len_for_unit_dist); 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; ) { + for (i = 0; i < pix_count - 2; ) { // 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); - } + const int max_len = MaxFindCopyLength(pix_count - i); + HashChainFindCopy(hash_chain, i, xsize, argb, max_len, window_size, + iter_max, len_for_unit_dist, &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 (len < (max_len >> 2)) { + // Evaluate Alternative#2: Insert the pixel at 'i' as literal, and code + // the pixels starting at 'i + 1' using backward reference. + HashChainFindCopy(hash_chain, i + 1, xsize, argb, max_len - 1, + window_size, iter_max, len_for_unit_dist, &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); + AddSingleLiteral(argb[i], use_color_cache, &hashers, refs); 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) { @@ -425,23 +421,18 @@ static int BackwardReferencesHashChain(int xsize, int ysize, } 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); - } + AddSingleLiteral(argb[i], use_color_cache, &hashers, refs); + HashChainInsert(hash_chain, &argb[i], i); ++i; } } + while (i < pix_count) { + // Handle the last (two) pixel(s). + AddSingleLiteral(argb[i], use_color_cache, &hashers, refs); + if (i < (pix_count - 1)) HashChainInsert(hash_chain, &argb[i], i); + ++i; + } + ok = !refs->error_; Error: if (cc_init) VP8LColorCacheClear(&hashers); @@ -536,13 +527,11 @@ static WEBP_INLINE double GetDistanceCost(const CostModel* const m, return m->distance_[code] + extra_bits; } -static void AddSingleLiteral(const uint32_t* const argb, - VP8LHashChain* const hash_chain, - VP8LColorCache* const hashers, - const CostModel* const cost_model, - int idx, int is_last, int use_color_cache, - double prev_cost, float* const cost, - uint32_t* const dist_array) { +static void AddSingleLiteralWithCostModel( + const uint32_t* const argb, VP8LHashChain* const hash_chain, + VP8LColorCache* const hashers, const CostModel* const cost_model, int idx, + int is_last, int use_color_cache, double prev_cost, float* const cost, + uint32_t* const dist_array) { double cost_val = prev_cost; const uint32_t color = argb[0]; if (!is_last) { @@ -582,9 +571,9 @@ static int BackwardReferencesHashChainDistanceOnly( (CostModel*)WebPSafeMalloc(1ULL, cost_model_size); VP8LColorCache hashers; const int min_distance_code = 2; - int window_size = WINDOW_SIZE; - int iter_pos = 1; - int iter_limit = -1; + int iter_max, len_for_unit_dist; + const int window_size = GetWindowSizeForHashChain(quality, xsize); + GetParamsForHashChainFindCopy(quality, &iter_max, &len_for_unit_dist); if (cost == NULL || cost_model == NULL) goto Error; @@ -603,19 +592,17 @@ static int BackwardReferencesHashChainDistanceOnly( // 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); // Add first pixel as literal. - AddSingleLiteral(argb + 0, hash_chain, &hashers, cost_model, 0, 0, - use_color_cache, 0.0, cost, dist_array); + AddSingleLiteralWithCostModel(argb + 0, hash_chain, &hashers, cost_model, 0, + 0, use_color_cache, 0.0, cost, dist_array); for (i = 1; i < pix_count - 1; ++i) { int offset = 0; int len = 0; double prev_cost = cost[i - 1]; - const int max_len = pix_count - i; + const int max_len = MaxFindCopyLength(pix_count - i); HashChainFindCopy(hash_chain, i, xsize, argb, max_len, window_size, - iter_pos, iter_limit, &offset, &len); + iter_max, len_for_unit_dist, &offset, &len); if (len >= MIN_LENGTH) { const int code = DistanceToPlaneCode(xsize, offset); const double distance_cost = @@ -630,7 +617,7 @@ static int BackwardReferencesHashChainDistanceOnly( } // This if is for speedup only. It roughly doubles the speed, and // makes compression worse by .1 %. - if (len >= 128 && code <= min_distance_code) { + if (len >= len_for_unit_dist && code <= min_distance_code) { // Long copy for short distances, let's skip the middle // lookups for better copies. // 1) insert the hashes. @@ -666,14 +653,16 @@ static int BackwardReferencesHashChainDistanceOnly( } } } - AddSingleLiteral(argb + i, hash_chain, &hashers, cost_model, i, 0, - use_color_cache, prev_cost, cost, dist_array); + AddSingleLiteralWithCostModel(argb + i, hash_chain, &hashers, cost_model, i, + 0, use_color_cache, prev_cost, cost, + dist_array); next_symbol: ; } // Handle the last pixel. if (i == (pix_count - 1)) { - AddSingleLiteral(argb + i, hash_chain, &hashers, cost_model, i, 1, - use_color_cache, cost[pix_count - 2], cost, dist_array); + AddSingleLiteralWithCostModel(argb + i, hash_chain, &hashers, cost_model, i, + 1, use_color_cache, cost[pix_count - 2], cost, + dist_array); } ok = !refs->error_; Error: @@ -710,15 +699,12 @@ static int BackwardReferencesHashChainFollowChosenPath( 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 i = 0; int ok = 0; + int size = 0; int cc_init = 0; - int window_size = WINDOW_SIZE; - int iter_pos = 1; - int iter_limit = -1; + const int window_size = GetWindowSizeForHashChain(quality, xsize); VP8LColorCache hashers; if (use_color_cache) { @@ -727,13 +713,12 @@ static int BackwardReferencesHashChainFollowChosenPath( } 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; const int len = chosen_path[ix]; if (len != 1) { + int k; HashChainFindOffset(hash_chain, i, argb, len, window_size, &offset); BackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(offset, len)); if (use_color_cache) {