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-rw-r--r--media/libwebp/src/enc/backward_references_cost_enc.c795
1 files changed, 795 insertions, 0 deletions
diff --git a/media/libwebp/src/enc/backward_references_cost_enc.c b/media/libwebp/src/enc/backward_references_cost_enc.c
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index 0000000000..6968ef3c9f
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+++ b/media/libwebp/src/enc/backward_references_cost_enc.c
@@ -0,0 +1,795 @@
+// Copyright 2017 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.
+// -----------------------------------------------------------------------------
+//
+// Improves a given set of backward references by analyzing its bit cost.
+// The algorithm is similar to the Zopfli compression algorithm but tailored to
+// images.
+//
+// Author: Vincent Rabaud (vrabaud@google.com)
+//
+
+#include <assert.h>
+#include <float.h>
+
+#include "src/dsp/lossless_common.h"
+#include "src/enc/backward_references_enc.h"
+#include "src/enc/histogram_enc.h"
+#include "src/utils/color_cache_utils.h"
+#include "src/utils/utils.h"
+
+#define VALUES_IN_BYTE 256
+
+extern void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs);
+extern int VP8LDistanceToPlaneCode(int xsize, int dist);
+extern void VP8LBackwardRefsCursorAdd(VP8LBackwardRefs* const refs,
+ const PixOrCopy v);
+
+typedef struct {
+ float alpha_[VALUES_IN_BYTE];
+ float red_[VALUES_IN_BYTE];
+ float blue_[VALUES_IN_BYTE];
+ float distance_[NUM_DISTANCE_CODES];
+ float* literal_;
+} CostModel;
+
+static void ConvertPopulationCountTableToBitEstimates(
+ int num_symbols, const uint32_t population_counts[], float 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 float 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 cache_bits,
+ const VP8LBackwardRefs* const refs) {
+ int ok = 0;
+ VP8LRefsCursor c = VP8LRefsCursorInit(refs);
+ VP8LHistogram* const histo = VP8LAllocateHistogram(cache_bits);
+ if (histo == NULL) goto Error;
+
+ // The following code is similar to VP8LHistogramCreate but converts the
+ // distance to plane code.
+ VP8LHistogramInit(histo, cache_bits, /*init_arrays=*/ 1);
+ while (VP8LRefsCursorOk(&c)) {
+ VP8LHistogramAddSinglePixOrCopy(histo, c.cur_pos, VP8LDistanceToPlaneCode,
+ xsize);
+ VP8LRefsCursorNext(&c);
+ }
+
+ 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 float 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 float 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 float 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 float GetDistanceCost(const CostModel* const m,
+ uint32_t distance) {
+ int code, extra_bits;
+ VP8LPrefixEncodeBits(distance, &code, &extra_bits);
+ return m->distance_[code] + extra_bits;
+}
+
+static WEBP_INLINE void AddSingleLiteralWithCostModel(
+ const uint32_t* const argb, VP8LColorCache* const hashers,
+ const CostModel* const cost_model, int idx, int use_color_cache,
+ float prev_cost, float* const cost, uint16_t* const dist_array) {
+ float cost_val = prev_cost;
+ const uint32_t color = argb[idx];
+ const int ix = use_color_cache ? VP8LColorCacheContains(hashers, color) : -1;
+ if (ix >= 0) {
+ // use_color_cache is true and hashers contains color
+ const float mul0 = 0.68f;
+ cost_val += GetCacheCost(cost_model, ix) * mul0;
+ } else {
+ const float mul1 = 0.82f;
+ if (use_color_cache) VP8LColorCacheInsert(hashers, color);
+ cost_val += GetLiteralCost(cost_model, color) * mul1;
+ }
+ if (cost[idx] > cost_val) {
+ cost[idx] = cost_val;
+ dist_array[idx] = 1; // only one is inserted.
+ }
+}
+
+// -----------------------------------------------------------------------------
+// CostManager and interval handling
+
+// Empirical value to avoid high memory consumption but good for performance.
+#define COST_CACHE_INTERVAL_SIZE_MAX 500
+
+// To perform backward reference every pixel at index index_ is considered and
+// the cost for the MAX_LENGTH following pixels computed. Those following pixels
+// at index index_ + k (k from 0 to MAX_LENGTH) have a cost of:
+// cost_ = distance cost at index + GetLengthCost(cost_model, k)
+// and the minimum value is kept. GetLengthCost(cost_model, k) is cached in an
+// array of size MAX_LENGTH.
+// Instead of performing MAX_LENGTH comparisons per pixel, we keep track of the
+// minimal values using intervals of constant cost.
+// An interval is defined by the index_ of the pixel that generated it and
+// is only useful in a range of indices from start_ to end_ (exclusive), i.e.
+// it contains the minimum value for pixels between start_ and end_.
+// Intervals are stored in a linked list and ordered by start_. When a new
+// interval has a better value, old intervals are split or removed. There are
+// therefore no overlapping intervals.
+typedef struct CostInterval CostInterval;
+struct CostInterval {
+ float cost_;
+ int start_;
+ int end_;
+ int index_;
+ CostInterval* previous_;
+ CostInterval* next_;
+};
+
+// The GetLengthCost(cost_model, k) are cached in a CostCacheInterval.
+typedef struct {
+ float cost_;
+ int start_;
+ int end_; // Exclusive.
+} CostCacheInterval;
+
+// This structure is in charge of managing intervals and costs.
+// It caches the different CostCacheInterval, caches the different
+// GetLengthCost(cost_model, k) in cost_cache_ and the CostInterval's (whose
+// count_ is limited by COST_CACHE_INTERVAL_SIZE_MAX).
+#define COST_MANAGER_MAX_FREE_LIST 10
+typedef struct {
+ CostInterval* head_;
+ int count_; // The number of stored intervals.
+ CostCacheInterval* cache_intervals_;
+ size_t cache_intervals_size_;
+ float cost_cache_[MAX_LENGTH]; // Contains the GetLengthCost(cost_model, k).
+ float* costs_;
+ uint16_t* dist_array_;
+ // Most of the time, we only need few intervals -> use a free-list, to avoid
+ // fragmentation with small allocs in most common cases.
+ CostInterval intervals_[COST_MANAGER_MAX_FREE_LIST];
+ CostInterval* free_intervals_;
+ // These are regularly malloc'd remains. This list can't grow larger than than
+ // size COST_CACHE_INTERVAL_SIZE_MAX - COST_MANAGER_MAX_FREE_LIST, note.
+ CostInterval* recycled_intervals_;
+} CostManager;
+
+static void CostIntervalAddToFreeList(CostManager* const manager,
+ CostInterval* const interval) {
+ interval->next_ = manager->free_intervals_;
+ manager->free_intervals_ = interval;
+}
+
+static int CostIntervalIsInFreeList(const CostManager* const manager,
+ const CostInterval* const interval) {
+ return (interval >= &manager->intervals_[0] &&
+ interval <= &manager->intervals_[COST_MANAGER_MAX_FREE_LIST - 1]);
+}
+
+static void CostManagerInitFreeList(CostManager* const manager) {
+ int i;
+ manager->free_intervals_ = NULL;
+ for (i = 0; i < COST_MANAGER_MAX_FREE_LIST; ++i) {
+ CostIntervalAddToFreeList(manager, &manager->intervals_[i]);
+ }
+}
+
+static void DeleteIntervalList(CostManager* const manager,
+ const CostInterval* interval) {
+ while (interval != NULL) {
+ const CostInterval* const next = interval->next_;
+ if (!CostIntervalIsInFreeList(manager, interval)) {
+ WebPSafeFree((void*)interval);
+ } // else: do nothing
+ interval = next;
+ }
+}
+
+static void CostManagerClear(CostManager* const manager) {
+ if (manager == NULL) return;
+
+ WebPSafeFree(manager->costs_);
+ WebPSafeFree(manager->cache_intervals_);
+
+ // Clear the interval lists.
+ DeleteIntervalList(manager, manager->head_);
+ manager->head_ = NULL;
+ DeleteIntervalList(manager, manager->recycled_intervals_);
+ manager->recycled_intervals_ = NULL;
+
+ // Reset pointers, count_ and cache_intervals_size_.
+ memset(manager, 0, sizeof(*manager));
+ CostManagerInitFreeList(manager);
+}
+
+static int CostManagerInit(CostManager* const manager,
+ uint16_t* const dist_array, int pix_count,
+ const CostModel* const cost_model) {
+ int i;
+ const int cost_cache_size = (pix_count > MAX_LENGTH) ? MAX_LENGTH : pix_count;
+
+ manager->costs_ = NULL;
+ manager->cache_intervals_ = NULL;
+ manager->head_ = NULL;
+ manager->recycled_intervals_ = NULL;
+ manager->count_ = 0;
+ manager->dist_array_ = dist_array;
+ CostManagerInitFreeList(manager);
+
+ // Fill in the cost_cache_.
+ // Has to be done in two passes due to a GCC bug on i686
+ // related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=323
+ for (i = 0; i < cost_cache_size; ++i) {
+ manager->cost_cache_[i] = GetLengthCost(cost_model, i);
+ }
+ manager->cache_intervals_size_ = 1;
+ for (i = 1; i < cost_cache_size; ++i) {
+ // Get the number of bound intervals.
+ if (manager->cost_cache_[i] != manager->cost_cache_[i - 1]) {
+ ++manager->cache_intervals_size_;
+ }
+ }
+
+ // With the current cost model, we usually have below 20 intervals.
+ // The worst case scenario with a cost model would be if every length has a
+ // different cost, hence MAX_LENGTH but that is impossible with the current
+ // implementation that spirals around a pixel.
+ assert(manager->cache_intervals_size_ <= MAX_LENGTH);
+ manager->cache_intervals_ = (CostCacheInterval*)WebPSafeMalloc(
+ manager->cache_intervals_size_, sizeof(*manager->cache_intervals_));
+ if (manager->cache_intervals_ == NULL) {
+ CostManagerClear(manager);
+ return 0;
+ }
+
+ // Fill in the cache_intervals_.
+ {
+ CostCacheInterval* cur = manager->cache_intervals_;
+
+ // Consecutive values in cost_cache_ are compared and if a big enough
+ // difference is found, a new interval is created and bounded.
+ cur->start_ = 0;
+ cur->end_ = 1;
+ cur->cost_ = manager->cost_cache_[0];
+ for (i = 1; i < cost_cache_size; ++i) {
+ const float cost_val = manager->cost_cache_[i];
+ if (cost_val != cur->cost_) {
+ ++cur;
+ // Initialize an interval.
+ cur->start_ = i;
+ cur->cost_ = cost_val;
+ }
+ cur->end_ = i + 1;
+ }
+ assert((size_t)(cur - manager->cache_intervals_) + 1 ==
+ manager->cache_intervals_size_);
+ }
+
+ manager->costs_ = (float*)WebPSafeMalloc(pix_count, sizeof(*manager->costs_));
+ if (manager->costs_ == NULL) {
+ CostManagerClear(manager);
+ return 0;
+ }
+ // Set the initial costs_ high for every pixel as we will keep the minimum.
+ for (i = 0; i < pix_count; ++i) manager->costs_[i] = FLT_MAX;
+
+ return 1;
+}
+
+// Given the cost and the position that define an interval, update the cost at
+// pixel 'i' if it is smaller than the previously computed value.
+static WEBP_INLINE void UpdateCost(CostManager* const manager, int i,
+ int position, float cost) {
+ const int k = i - position;
+ assert(k >= 0 && k < MAX_LENGTH);
+
+ if (manager->costs_[i] > cost) {
+ manager->costs_[i] = cost;
+ manager->dist_array_[i] = k + 1;
+ }
+}
+
+// Given the cost and the position that define an interval, update the cost for
+// all the pixels between 'start' and 'end' excluded.
+static WEBP_INLINE void UpdateCostPerInterval(CostManager* const manager,
+ int start, int end, int position,
+ float cost) {
+ int i;
+ for (i = start; i < end; ++i) UpdateCost(manager, i, position, cost);
+}
+
+// Given two intervals, make 'prev' be the previous one of 'next' in 'manager'.
+static WEBP_INLINE void ConnectIntervals(CostManager* const manager,
+ CostInterval* const prev,
+ CostInterval* const next) {
+ if (prev != NULL) {
+ prev->next_ = next;
+ } else {
+ manager->head_ = next;
+ }
+
+ if (next != NULL) next->previous_ = prev;
+}
+
+// Pop an interval in the manager.
+static WEBP_INLINE void PopInterval(CostManager* const manager,
+ CostInterval* const interval) {
+ if (interval == NULL) return;
+
+ ConnectIntervals(manager, interval->previous_, interval->next_);
+ if (CostIntervalIsInFreeList(manager, interval)) {
+ CostIntervalAddToFreeList(manager, interval);
+ } else { // recycle regularly malloc'd intervals too
+ interval->next_ = manager->recycled_intervals_;
+ manager->recycled_intervals_ = interval;
+ }
+ --manager->count_;
+ assert(manager->count_ >= 0);
+}
+
+// Update the cost at index i by going over all the stored intervals that
+// overlap with i.
+// If 'do_clean_intervals' is set to something different than 0, intervals that
+// end before 'i' will be popped.
+static WEBP_INLINE void UpdateCostAtIndex(CostManager* const manager, int i,
+ int do_clean_intervals) {
+ CostInterval* current = manager->head_;
+
+ while (current != NULL && current->start_ <= i) {
+ CostInterval* const next = current->next_;
+ if (current->end_ <= i) {
+ if (do_clean_intervals) {
+ // We have an outdated interval, remove it.
+ PopInterval(manager, current);
+ }
+ } else {
+ UpdateCost(manager, i, current->index_, current->cost_);
+ }
+ current = next;
+ }
+}
+
+// Given a current orphan interval and its previous interval, before
+// it was orphaned (which can be NULL), set it at the right place in the list
+// of intervals using the start_ ordering and the previous interval as a hint.
+static WEBP_INLINE void PositionOrphanInterval(CostManager* const manager,
+ CostInterval* const current,
+ CostInterval* previous) {
+ assert(current != NULL);
+
+ if (previous == NULL) previous = manager->head_;
+ while (previous != NULL && current->start_ < previous->start_) {
+ previous = previous->previous_;
+ }
+ while (previous != NULL && previous->next_ != NULL &&
+ previous->next_->start_ < current->start_) {
+ previous = previous->next_;
+ }
+
+ if (previous != NULL) {
+ ConnectIntervals(manager, current, previous->next_);
+ } else {
+ ConnectIntervals(manager, current, manager->head_);
+ }
+ ConnectIntervals(manager, previous, current);
+}
+
+// Insert an interval in the list contained in the manager by starting at
+// interval_in as a hint. The intervals are sorted by start_ value.
+static WEBP_INLINE void InsertInterval(CostManager* const manager,
+ CostInterval* const interval_in,
+ float cost, int position, int start,
+ int end) {
+ CostInterval* interval_new;
+
+ if (start >= end) return;
+ if (manager->count_ >= COST_CACHE_INTERVAL_SIZE_MAX) {
+ // Serialize the interval if we cannot store it.
+ UpdateCostPerInterval(manager, start, end, position, cost);
+ return;
+ }
+ if (manager->free_intervals_ != NULL) {
+ interval_new = manager->free_intervals_;
+ manager->free_intervals_ = interval_new->next_;
+ } else if (manager->recycled_intervals_ != NULL) {
+ interval_new = manager->recycled_intervals_;
+ manager->recycled_intervals_ = interval_new->next_;
+ } else { // malloc for good
+ interval_new = (CostInterval*)WebPSafeMalloc(1, sizeof(*interval_new));
+ if (interval_new == NULL) {
+ // Write down the interval if we cannot create it.
+ UpdateCostPerInterval(manager, start, end, position, cost);
+ return;
+ }
+ }
+
+ interval_new->cost_ = cost;
+ interval_new->index_ = position;
+ interval_new->start_ = start;
+ interval_new->end_ = end;
+ PositionOrphanInterval(manager, interval_new, interval_in);
+
+ ++manager->count_;
+}
+
+// Given a new cost interval defined by its start at position, its length value
+// and distance_cost, add its contributions to the previous intervals and costs.
+// If handling the interval or one of its subintervals becomes to heavy, its
+// contribution is added to the costs right away.
+static WEBP_INLINE void PushInterval(CostManager* const manager,
+ float distance_cost, int position,
+ int len) {
+ size_t i;
+ CostInterval* interval = manager->head_;
+ CostInterval* interval_next;
+ const CostCacheInterval* const cost_cache_intervals =
+ manager->cache_intervals_;
+ // If the interval is small enough, no need to deal with the heavy
+ // interval logic, just serialize it right away. This constant is empirical.
+ const int kSkipDistance = 10;
+
+ if (len < kSkipDistance) {
+ int j;
+ for (j = position; j < position + len; ++j) {
+ const int k = j - position;
+ float cost_tmp;
+ assert(k >= 0 && k < MAX_LENGTH);
+ cost_tmp = distance_cost + manager->cost_cache_[k];
+
+ if (manager->costs_[j] > cost_tmp) {
+ manager->costs_[j] = cost_tmp;
+ manager->dist_array_[j] = k + 1;
+ }
+ }
+ return;
+ }
+
+ for (i = 0; i < manager->cache_intervals_size_ &&
+ cost_cache_intervals[i].start_ < len;
+ ++i) {
+ // Define the intersection of the ith interval with the new one.
+ int start = position + cost_cache_intervals[i].start_;
+ const int end = position + (cost_cache_intervals[i].end_ > len
+ ? len
+ : cost_cache_intervals[i].end_);
+ const float cost = distance_cost + cost_cache_intervals[i].cost_;
+
+ for (; interval != NULL && interval->start_ < end;
+ interval = interval_next) {
+ interval_next = interval->next_;
+
+ // Make sure we have some overlap
+ if (start >= interval->end_) continue;
+
+ if (cost >= interval->cost_) {
+ // When intervals are represented, the lower, the better.
+ // [**********************************************************[
+ // start end
+ // [----------------------------------[
+ // interval->start_ interval->end_
+ // If we are worse than what we already have, add whatever we have so
+ // far up to interval.
+ const int start_new = interval->end_;
+ InsertInterval(manager, interval, cost, position, start,
+ interval->start_);
+ start = start_new;
+ if (start >= end) break;
+ continue;
+ }
+
+ if (start <= interval->start_) {
+ if (interval->end_ <= end) {
+ // [----------------------------------[
+ // interval->start_ interval->end_
+ // [**************************************************************[
+ // start end
+ // We can safely remove the old interval as it is fully included.
+ PopInterval(manager, interval);
+ } else {
+ // [------------------------------------[
+ // interval->start_ interval->end_
+ // [*****************************[
+ // start end
+ interval->start_ = end;
+ break;
+ }
+ } else {
+ if (end < interval->end_) {
+ // [--------------------------------------------------------------[
+ // interval->start_ interval->end_
+ // [*****************************[
+ // start end
+ // We have to split the old interval as it fully contains the new one.
+ const int end_original = interval->end_;
+ interval->end_ = start;
+ InsertInterval(manager, interval, interval->cost_, interval->index_,
+ end, end_original);
+ interval = interval->next_;
+ break;
+ } else {
+ // [------------------------------------[
+ // interval->start_ interval->end_
+ // [*****************************[
+ // start end
+ interval->end_ = start;
+ }
+ }
+ }
+ // Insert the remaining interval from start to end.
+ InsertInterval(manager, interval, cost, position, start, end);
+ }
+}
+
+static int BackwardReferencesHashChainDistanceOnly(
+ int xsize, int ysize, const uint32_t* const argb, int cache_bits,
+ const VP8LHashChain* const hash_chain, const VP8LBackwardRefs* const refs,
+ uint16_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);
+ const size_t literal_array_size =
+ sizeof(float) * (VP8LHistogramNumCodes(cache_bits));
+ const size_t cost_model_size = sizeof(CostModel) + literal_array_size;
+ CostModel* const cost_model =
+ (CostModel*)WebPSafeCalloc(1ULL, cost_model_size);
+ VP8LColorCache hashers;
+ CostManager* cost_manager =
+ (CostManager*)WebPSafeCalloc(1ULL, sizeof(*cost_manager));
+ int offset_prev = -1, len_prev = -1;
+ float offset_cost = -1.f;
+ int first_offset_is_constant = -1; // initialized with 'impossible' value
+ int reach = 0;
+
+ if (cost_model == NULL || cost_manager == NULL) goto Error;
+
+ cost_model->literal_ = (float*)(cost_model + 1);
+ if (use_color_cache) {
+ cc_init = VP8LColorCacheInit(&hashers, cache_bits);
+ if (!cc_init) goto Error;
+ }
+
+ if (!CostModelBuild(cost_model, xsize, cache_bits, refs)) {
+ goto Error;
+ }
+
+ if (!CostManagerInit(cost_manager, dist_array, pix_count, cost_model)) {
+ goto Error;
+ }
+
+ // We loop one pixel at a time, but store all currently best points to
+ // non-processed locations from this point.
+ dist_array[0] = 0;
+ // Add first pixel as literal.
+ AddSingleLiteralWithCostModel(argb, &hashers, cost_model, 0, use_color_cache,
+ 0.f, cost_manager->costs_, dist_array);
+
+ for (i = 1; i < pix_count; ++i) {
+ const float prev_cost = cost_manager->costs_[i - 1];
+ int offset, len;
+ VP8LHashChainFindCopy(hash_chain, i, &offset, &len);
+
+ // Try adding the pixel as a literal.
+ AddSingleLiteralWithCostModel(argb, &hashers, cost_model, i,
+ use_color_cache, prev_cost,
+ cost_manager->costs_, dist_array);
+
+ // If we are dealing with a non-literal.
+ if (len >= 2) {
+ if (offset != offset_prev) {
+ const int code = VP8LDistanceToPlaneCode(xsize, offset);
+ offset_cost = GetDistanceCost(cost_model, code);
+ first_offset_is_constant = 1;
+ PushInterval(cost_manager, prev_cost + offset_cost, i, len);
+ } else {
+ assert(offset_cost >= 0);
+ assert(len_prev >= 0);
+ assert(first_offset_is_constant == 0 || first_offset_is_constant == 1);
+ // Instead of considering all contributions from a pixel i by calling:
+ // PushInterval(cost_manager, prev_cost + offset_cost, i, len);
+ // we optimize these contributions in case offset_cost stays the same
+ // for consecutive pixels. This describes a set of pixels similar to a
+ // previous set (e.g. constant color regions).
+ if (first_offset_is_constant) {
+ reach = i - 1 + len_prev - 1;
+ first_offset_is_constant = 0;
+ }
+
+ if (i + len - 1 > reach) {
+ // We can only be go further with the same offset if the previous
+ // length was maxed, hence len_prev == len == MAX_LENGTH.
+ // TODO(vrabaud), bump i to the end right away (insert cache and
+ // update cost).
+ // TODO(vrabaud), check if one of the points in between does not have
+ // a lower cost.
+ // Already consider the pixel at "reach" to add intervals that are
+ // better than whatever we add.
+ int offset_j, len_j = 0;
+ int j;
+ assert(len == MAX_LENGTH || len == pix_count - i);
+ // Figure out the last consecutive pixel within [i, reach + 1] with
+ // the same offset.
+ for (j = i; j <= reach; ++j) {
+ VP8LHashChainFindCopy(hash_chain, j + 1, &offset_j, &len_j);
+ if (offset_j != offset) {
+ VP8LHashChainFindCopy(hash_chain, j, &offset_j, &len_j);
+ break;
+ }
+ }
+ // Update the cost at j - 1 and j.
+ UpdateCostAtIndex(cost_manager, j - 1, 0);
+ UpdateCostAtIndex(cost_manager, j, 0);
+
+ PushInterval(cost_manager, cost_manager->costs_[j - 1] + offset_cost,
+ j, len_j);
+ reach = j + len_j - 1;
+ }
+ }
+ }
+
+ UpdateCostAtIndex(cost_manager, i, 1);
+ offset_prev = offset;
+ len_prev = len;
+ }
+
+ ok = !refs->error_;
+ Error:
+ if (cc_init) VP8LColorCacheClear(&hashers);
+ CostManagerClear(cost_manager);
+ WebPSafeFree(cost_model);
+ WebPSafeFree(cost_manager);
+ 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(uint16_t* const dist_array,
+ int dist_array_size,
+ uint16_t** const chosen_path,
+ int* const chosen_path_size) {
+ uint16_t* path = dist_array + dist_array_size;
+ uint16_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(
+ const uint32_t* const argb, int cache_bits,
+ const uint16_t* const chosen_path, int chosen_path_size,
+ const VP8LHashChain* const hash_chain, VP8LBackwardRefs* const refs) {
+ const int use_color_cache = (cache_bits > 0);
+ int ix;
+ int i = 0;
+ int ok = 0;
+ int cc_init = 0;
+ VP8LColorCache hashers;
+
+ if (use_color_cache) {
+ cc_init = VP8LColorCacheInit(&hashers, cache_bits);
+ if (!cc_init) goto Error;
+ }
+
+ VP8LClearBackwardRefs(refs);
+ for (ix = 0; ix < chosen_path_size; ++ix) {
+ const int len = chosen_path[ix];
+ if (len != 1) {
+ int k;
+ const int offset = VP8LHashChainFindOffset(hash_chain, i);
+ VP8LBackwardRefsCursorAdd(refs, PixOrCopyCreateCopy(offset, len));
+ if (use_color_cache) {
+ for (k = 0; k < len; ++k) {
+ VP8LColorCacheInsert(&hashers, argb[i + k]);
+ }
+ }
+ i += len;
+ } else {
+ PixOrCopy v;
+ const int idx =
+ use_color_cache ? VP8LColorCacheContains(&hashers, argb[i]) : -1;
+ if (idx >= 0) {
+ // use_color_cache is true and hashers contains argb[i]
+ // push pixel as a color cache index
+ v = PixOrCopyCreateCacheIdx(idx);
+ } else {
+ if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
+ v = PixOrCopyCreateLiteral(argb[i]);
+ }
+ VP8LBackwardRefsCursorAdd(refs, v);
+ ++i;
+ }
+ }
+ ok = !refs->error_;
+ Error:
+ if (cc_init) VP8LColorCacheClear(&hashers);
+ return ok;
+}
+
+// Returns 1 on success.
+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);
+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) {
+ int ok = 0;
+ const int dist_array_size = xsize * ysize;
+ uint16_t* chosen_path = NULL;
+ int chosen_path_size = 0;
+ uint16_t* dist_array =
+ (uint16_t*)WebPSafeMalloc(dist_array_size, sizeof(*dist_array));
+
+ if (dist_array == NULL) goto Error;
+
+ if (!BackwardReferencesHashChainDistanceOnly(
+ xsize, ysize, argb, cache_bits, hash_chain, refs_src, dist_array)) {
+ goto Error;
+ }
+ TraceBackwards(dist_array, dist_array_size, &chosen_path, &chosen_path_size);
+ if (!BackwardReferencesHashChainFollowChosenPath(
+ argb, cache_bits, chosen_path, chosen_path_size, hash_chain,
+ refs_dst)) {
+ goto Error;
+ }
+ ok = 1;
+ Error:
+ WebPSafeFree(dist_array);
+ return ok;
+}