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+// 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)
+//
+
+#ifndef WEBP_ENC_BACKWARD_REFERENCES_H_
+#define WEBP_ENC_BACKWARD_REFERENCES_H_
+
+#include <assert.h>
+#include <stdlib.h>
+#include "../webp/types.h"
+#include "../webp/format_constants.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// The maximum allowed limit is 11.
+#define MAX_COLOR_CACHE_BITS 10
+
+// -----------------------------------------------------------------------------
+// PixOrCopy
+
+enum Mode {
+ kLiteral,
+ kCacheIdx,
+ kCopy,
+ kNone
+};
+
+typedef struct {
+ // mode as uint8_t to make the memory layout to be exactly 8 bytes.
+ uint8_t mode;
+ uint16_t len;
+ uint32_t argb_or_distance;
+} PixOrCopy;
+
+static WEBP_INLINE PixOrCopy PixOrCopyCreateCopy(uint32_t distance,
+ uint16_t len) {
+ PixOrCopy retval;
+ retval.mode = kCopy;
+ retval.argb_or_distance = distance;
+ retval.len = len;
+ return retval;
+}
+
+static WEBP_INLINE PixOrCopy PixOrCopyCreateCacheIdx(int idx) {
+ PixOrCopy retval;
+ assert(idx >= 0);
+ assert(idx < (1 << MAX_COLOR_CACHE_BITS));
+ retval.mode = kCacheIdx;
+ retval.argb_or_distance = idx;
+ retval.len = 1;
+ return retval;
+}
+
+static WEBP_INLINE PixOrCopy PixOrCopyCreateLiteral(uint32_t argb) {
+ PixOrCopy retval;
+ retval.mode = kLiteral;
+ retval.argb_or_distance = argb;
+ retval.len = 1;
+ return retval;
+}
+
+static WEBP_INLINE int PixOrCopyIsLiteral(const PixOrCopy* const p) {
+ return (p->mode == kLiteral);
+}
+
+static WEBP_INLINE int PixOrCopyIsCacheIdx(const PixOrCopy* const p) {
+ return (p->mode == kCacheIdx);
+}
+
+static WEBP_INLINE int PixOrCopyIsCopy(const PixOrCopy* const p) {
+ return (p->mode == kCopy);
+}
+
+static WEBP_INLINE uint32_t PixOrCopyLiteral(const PixOrCopy* const p,
+ int component) {
+ assert(p->mode == kLiteral);
+ return (p->argb_or_distance >> (component * 8)) & 0xff;
+}
+
+static WEBP_INLINE uint32_t PixOrCopyLength(const PixOrCopy* const p) {
+ return p->len;
+}
+
+static WEBP_INLINE uint32_t PixOrCopyArgb(const PixOrCopy* const p) {
+ assert(p->mode == kLiteral);
+ return p->argb_or_distance;
+}
+
+static WEBP_INLINE uint32_t PixOrCopyCacheIdx(const PixOrCopy* const p) {
+ assert(p->mode == kCacheIdx);
+ assert(p->argb_or_distance < (1U << MAX_COLOR_CACHE_BITS));
+ return p->argb_or_distance;
+}
+
+static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) {
+ assert(p->mode == kCopy);
+ return p->argb_or_distance;
+}
+
+// -----------------------------------------------------------------------------
+// VP8LHashChain
+
+#define HASH_BITS 18
+#define HASH_SIZE (1 << HASH_BITS)
+
+typedef struct VP8LHashChain VP8LHashChain;
+struct VP8LHashChain {
+ // The 20 most significant bits contain the offset at which the best match
+ // is found. These 20 bits are the limit defined by GetWindowSizeForHashChain
+ // (through WINDOW_SIZE = 1<<20).
+ // The lower 12 bits contain the length of the match. The 12 bit limit is
+ // defined in MaxFindCopyLength with MAX_LENGTH=4096.
+ uint32_t* offset_length_;
+ // This is the maximum size of the hash_chain that can be constructed.
+ // Typically this is the pixel count (width x height) for a given image.
+ int size_;
+};
+
+// Must be called first, to set size.
+int VP8LHashChainInit(VP8LHashChain* const p, int size);
+// Pre-compute the best matches for argb.
+int VP8LHashChainFill(VP8LHashChain* const p, int quality,
+ const uint32_t* const argb, int xsize, int ysize,
+ int low_effort);
+void VP8LHashChainClear(VP8LHashChain* const p); // release memory
+
+// -----------------------------------------------------------------------------
+// VP8LBackwardRefs (block-based backward-references storage)
+
+// maximum number of reference blocks the image will be segmented into
+#define MAX_REFS_BLOCK_PER_IMAGE 16
+
+typedef struct PixOrCopyBlock PixOrCopyBlock; // forward declaration
+typedef struct VP8LBackwardRefs VP8LBackwardRefs;
+
+// Container for blocks chain
+struct VP8LBackwardRefs {
+ int block_size_; // common block-size
+ int error_; // set to true if some memory error occurred
+ PixOrCopyBlock* refs_; // list of currently used blocks
+ PixOrCopyBlock** tail_; // for list recycling
+ PixOrCopyBlock* free_blocks_; // free-list
+ PixOrCopyBlock* last_block_; // used for adding new refs (internal)
+};
+
+// Initialize the object. 'block_size' is the common block size to store
+// references (typically, width * height / MAX_REFS_BLOCK_PER_IMAGE).
+void VP8LBackwardRefsInit(VP8LBackwardRefs* const refs, int block_size);
+// Release memory for backward references.
+void VP8LBackwardRefsClear(VP8LBackwardRefs* const refs);
+// Copies the 'src' backward refs to the 'dst'. Returns 0 in case of error.
+int VP8LBackwardRefsCopy(const VP8LBackwardRefs* const src,
+ VP8LBackwardRefs* const dst);
+
+// Cursor for iterating on references content
+typedef struct {
+ // public:
+ PixOrCopy* cur_pos; // current position
+ // private:
+ PixOrCopyBlock* cur_block_; // current block in the refs list
+ const PixOrCopy* last_pos_; // sentinel for switching to next block
+} VP8LRefsCursor;
+
+// Returns a cursor positioned at the beginning of the references list.
+VP8LRefsCursor VP8LRefsCursorInit(const VP8LBackwardRefs* const refs);
+// Returns true if cursor is pointing at a valid position.
+static WEBP_INLINE int VP8LRefsCursorOk(const VP8LRefsCursor* const c) {
+ return (c->cur_pos != NULL);
+}
+// Move to next block of references. Internal, not to be called directly.
+void VP8LRefsCursorNextBlock(VP8LRefsCursor* const c);
+// Move to next position, or NULL. Should not be called if !VP8LRefsCursorOk().
+static WEBP_INLINE void VP8LRefsCursorNext(VP8LRefsCursor* const c) {
+ assert(c != NULL);
+ assert(VP8LRefsCursorOk(c));
+ if (++c->cur_pos == c->last_pos_) VP8LRefsCursorNextBlock(c);
+}
+
+// -----------------------------------------------------------------------------
+// Main entry points
+
+// Evaluates best possible backward references for specified quality.
+// The input cache_bits to 'VP8LGetBackwardReferences' sets the maximum cache
+// bits to use (passing 0 implies disabling the local color cache).
+// The optimal cache bits is evaluated and set for the *cache_bits parameter.
+// The return value is the pointer to the best of the two backward refs viz,
+// refs[0] or refs[1].
+VP8LBackwardRefs* VP8LGetBackwardReferences(
+ int width, int height, const uint32_t* const argb, int quality,
+ int low_effort, int* const cache_bits,
+ const VP8LHashChain* const hash_chain, VP8LBackwardRefs refs[2]);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // WEBP_ENC_BACKWARD_REFERENCES_H_