// 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" #if defined(__cplusplus) || defined(c_plusplus) 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)) // ----------------------------------------------------------------------------- // PrefixEncode() // use GNU builtins where available. #if defined(__GNUC__) && \ ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4) static WEBP_INLINE int BitsLog2Floor(uint32_t n) { assert(n != 0); return 31 ^ __builtin_clz(n); } #elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86)) #include <intrin.h> #pragma intrinsic(_BitScanReverse) static WEBP_INLINE int BitsLog2Floor(uint32_t n) { unsigned long first_set_bit; assert(n != 0); _BitScanReverse(&first_set_bit, n); return first_set_bit; } #else // Returns (int)floor(log2(n)). n must be > 0. static WEBP_INLINE int BitsLog2Floor(uint32_t n) { int log = 0; uint32_t value = n; int i; assert(n != 0); for (i = 4; i >= 0; --i) { const int shift = (1 << i); const uint32_t x = value >> shift; if (x != 0) { value = x; log += shift; } } return log; } #endif static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) { const int log_floor = BitsLog2Floor(n); if (n == (n & ~(n - 1))) // zero or a power of two. return log_floor; else return log_floor + 1; } // Splitting of distance and length codes into prefixes and // extra bits. The prefixes are encoded with an entropy code // while the extra bits are stored just as normal bits. static WEBP_INLINE void PrefixEncode(int distance, int* const code, int* const extra_bits_count, int* const extra_bits_value) { if (distance > 2) { // Collect the two most significant bits. const int highest_bit = BitsLog2Floor(--distance); const int second_highest_bit = (distance >> (highest_bit - 1)) & 1; *extra_bits_count = highest_bit - 1; *extra_bits_value = distance & ((1 << *extra_bits_count) - 1); *code = 2 * highest_bit + second_highest_bit; } else { *extra_bits_count = 0; *extra_bits_value = 0; *code = (distance == 2) ? 1 : 0; } } // ----------------------------------------------------------------------------- // 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); #if defined(__cplusplus) || defined(c_plusplus) } #endif #endif // WEBP_ENC_BACKWARD_REFERENCES_H_