third_party/libwebp/enc/backward_references.h

// 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 spec allows 11, we use 9 bits to reduce memory consumption in encoding.
// Having 9 instead of 11 only removes about 0.25 % of compression density.
#define MAX_COLOR_CACHE_BITS 9

// Max ever number of codes we'll use:
#define PIX_OR_COPY_CODES_MAX \
    (NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS))

// -----------------------------------------------------------------------------
// 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;
}

// -----------------------------------------------------------------------------
// VP8LBackwardRefs

typedef struct {
  PixOrCopy* refs;
  int size;      // currently used
  int max_size;  // maximum capacity
} VP8LBackwardRefs;

// Initialize the object. Must be called first. 'refs' can be NULL.
void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs);

// Release memory and re-initialize the object. 'refs' can be NULL.
void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs);

// Allocate 'max_size' references. Returns false in case of memory error.
int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size);

// -----------------------------------------------------------------------------
// Main entry points

// Evaluates best possible backward references for specified quality.
// Further optimize for 2D locality if use_2d_locality flag is set.
int VP8LGetBackwardReferences(int width, int height,
                              const uint32_t* const argb,
                              int quality, int cache_bits, int use_2d_locality,
                              VP8LBackwardRefs* const best);

// Produce an estimate for a good color cache size for the image.
int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
                                      int xsize, int ysize,
                                      int* const best_cache_bits);

#ifdef __cplusplus
}
#endif

#endif  // WEBP_ENC_BACKWARD_REFERENCES_H_