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220 lines
6.6 KiB
C
220 lines
6.6 KiB
C
// Copyright 2012 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Author: Jyrki Alakuijala (jyrki@google.com)
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//
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#ifndef WEBP_ENC_BACKWARD_REFERENCES_H_
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#define WEBP_ENC_BACKWARD_REFERENCES_H_
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#include <assert.h>
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#include <stdlib.h>
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#include "../webp/types.h"
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#include "../webp/format_constants.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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// The spec allows 11, we use 9 bits to reduce memory consumption in encoding.
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// Having 9 instead of 11 only removes about 0.25 % of compression density.
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#define MAX_COLOR_CACHE_BITS 9
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// Max ever number of codes we'll use:
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#define PIX_OR_COPY_CODES_MAX \
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(NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS))
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// -----------------------------------------------------------------------------
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// PrefixEncode()
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// use GNU builtins where available.
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#if defined(__GNUC__) && \
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((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
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static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
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assert(n != 0);
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return 31 ^ __builtin_clz(n);
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}
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#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86))
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#include <intrin.h>
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#pragma intrinsic(_BitScanReverse)
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static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
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unsigned long first_set_bit;
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assert(n != 0);
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_BitScanReverse(&first_set_bit, n);
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return first_set_bit;
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}
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#else
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// Returns (int)floor(log2(n)). n must be > 0.
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static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
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int log = 0;
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uint32_t value = n;
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int i;
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assert(n != 0);
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for (i = 4; i >= 0; --i) {
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const int shift = (1 << i);
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const uint32_t x = value >> shift;
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if (x != 0) {
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value = x;
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log += shift;
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}
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}
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return log;
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}
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#endif
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static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) {
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const int log_floor = BitsLog2Floor(n);
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if (n == (n & ~(n - 1))) // zero or a power of two.
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return log_floor;
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else
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return log_floor + 1;
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}
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// Splitting of distance and length codes into prefixes and
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// extra bits. The prefixes are encoded with an entropy code
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// while the extra bits are stored just as normal bits.
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static WEBP_INLINE void PrefixEncode(int distance, int* const code,
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int* const extra_bits_count,
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int* const extra_bits_value) {
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if (distance > 2) { // Collect the two most significant bits.
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const int highest_bit = BitsLog2Floor(--distance);
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const int second_highest_bit = (distance >> (highest_bit - 1)) & 1;
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*extra_bits_count = highest_bit - 1;
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*extra_bits_value = distance & ((1 << *extra_bits_count) - 1);
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*code = 2 * highest_bit + second_highest_bit;
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} else {
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*extra_bits_count = 0;
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*extra_bits_value = 0;
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*code = (distance == 2) ? 1 : 0;
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}
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}
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// -----------------------------------------------------------------------------
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// PixOrCopy
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enum Mode {
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kLiteral,
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kCacheIdx,
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kCopy,
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kNone
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};
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typedef struct {
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// mode as uint8_t to make the memory layout to be exactly 8 bytes.
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uint8_t mode;
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uint16_t len;
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uint32_t argb_or_distance;
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} PixOrCopy;
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static WEBP_INLINE PixOrCopy PixOrCopyCreateCopy(uint32_t distance,
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uint16_t len) {
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PixOrCopy retval;
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retval.mode = kCopy;
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retval.argb_or_distance = distance;
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retval.len = len;
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return retval;
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}
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static WEBP_INLINE PixOrCopy PixOrCopyCreateCacheIdx(int idx) {
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PixOrCopy retval;
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assert(idx >= 0);
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assert(idx < (1 << MAX_COLOR_CACHE_BITS));
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retval.mode = kCacheIdx;
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retval.argb_or_distance = idx;
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retval.len = 1;
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return retval;
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}
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static WEBP_INLINE PixOrCopy PixOrCopyCreateLiteral(uint32_t argb) {
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PixOrCopy retval;
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retval.mode = kLiteral;
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retval.argb_or_distance = argb;
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retval.len = 1;
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return retval;
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}
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static WEBP_INLINE int PixOrCopyIsLiteral(const PixOrCopy* const p) {
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return (p->mode == kLiteral);
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}
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static WEBP_INLINE int PixOrCopyIsCacheIdx(const PixOrCopy* const p) {
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return (p->mode == kCacheIdx);
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}
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static WEBP_INLINE int PixOrCopyIsCopy(const PixOrCopy* const p) {
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return (p->mode == kCopy);
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}
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static WEBP_INLINE uint32_t PixOrCopyLiteral(const PixOrCopy* const p,
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int component) {
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assert(p->mode == kLiteral);
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return (p->argb_or_distance >> (component * 8)) & 0xff;
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}
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static WEBP_INLINE uint32_t PixOrCopyLength(const PixOrCopy* const p) {
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return p->len;
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}
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static WEBP_INLINE uint32_t PixOrCopyArgb(const PixOrCopy* const p) {
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assert(p->mode == kLiteral);
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return p->argb_or_distance;
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}
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static WEBP_INLINE uint32_t PixOrCopyCacheIdx(const PixOrCopy* const p) {
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assert(p->mode == kCacheIdx);
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assert(p->argb_or_distance < (1U << MAX_COLOR_CACHE_BITS));
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return p->argb_or_distance;
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}
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static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) {
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assert(p->mode == kCopy);
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return p->argb_or_distance;
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}
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// -----------------------------------------------------------------------------
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// VP8LBackwardRefs
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typedef struct {
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PixOrCopy* refs;
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int size; // currently used
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int max_size; // maximum capacity
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} VP8LBackwardRefs;
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// Initialize the object. Must be called first. 'refs' can be NULL.
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void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs);
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// Release memory and re-initialize the object. 'refs' can be NULL.
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void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs);
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// Allocate 'max_size' references. Returns false in case of memory error.
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int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size);
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// -----------------------------------------------------------------------------
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// Main entry points
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// Evaluates best possible backward references for specified quality.
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// Further optimize for 2D locality if use_2d_locality flag is set.
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int VP8LGetBackwardReferences(int width, int height,
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const uint32_t* const argb,
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int quality, int cache_bits, int use_2d_locality,
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VP8LBackwardRefs* const best);
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// Produce an estimate for a good color cache size for the image.
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int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
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int xsize, int ysize,
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int* const best_cache_bits);
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#if defined(__cplusplus) || defined(c_plusplus)
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}
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#endif
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#endif // WEBP_ENC_BACKWARD_REFERENCES_H_
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