1 // Copyright 2012 Google Inc. All Rights Reserved. 2 // 3 // Use of this source code is governed by a BSD-style license 4 // that can be found in the COPYING file in the root of the source 5 // tree. An additional intellectual property rights grant can be found 6 // in the file PATENTS. All contributing project authors may 7 // be found in the AUTHORS file in the root of the source tree. 8 // ----------------------------------------------------------------------------- 9 // 10 // Author: Jyrki Alakuijala (jyrki (at) google.com) 11 // 12 13 #ifndef WEBP_ENC_BACKWARD_REFERENCES_H_ 14 #define WEBP_ENC_BACKWARD_REFERENCES_H_ 15 16 #include <assert.h> 17 #include <stdlib.h> 18 #include "../webp/types.h" 19 #include "../webp/format_constants.h" 20 21 #if defined(__cplusplus) || defined(c_plusplus) 22 extern "C" { 23 #endif 24 25 // The spec allows 11, we use 9 bits to reduce memory consumption in encoding. 26 // Having 9 instead of 11 only removes about 0.25 % of compression density. 27 #define MAX_COLOR_CACHE_BITS 9 28 29 // Max ever number of codes we'll use: 30 #define PIX_OR_COPY_CODES_MAX \ 31 (NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS)) 32 33 // ----------------------------------------------------------------------------- 34 // PrefixEncode() 35 36 // use GNU builtins where available. 37 #if defined(__GNUC__) && \ 38 ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4) 39 static WEBP_INLINE int BitsLog2Floor(uint32_t n) { 40 assert(n != 0); 41 return 31 ^ __builtin_clz(n); 42 } 43 #elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86)) 44 #include <intrin.h> 45 #pragma intrinsic(_BitScanReverse) 46 47 static WEBP_INLINE int BitsLog2Floor(uint32_t n) { 48 unsigned long first_set_bit; 49 assert(n != 0); 50 _BitScanReverse(&first_set_bit, n); 51 return first_set_bit; 52 } 53 #else 54 // Returns (int)floor(log2(n)). n must be > 0. 55 static WEBP_INLINE int BitsLog2Floor(uint32_t n) { 56 int log = 0; 57 uint32_t value = n; 58 int i; 59 60 assert(n != 0); 61 for (i = 4; i >= 0; --i) { 62 const int shift = (1 << i); 63 const uint32_t x = value >> shift; 64 if (x != 0) { 65 value = x; 66 log += shift; 67 } 68 } 69 return log; 70 } 71 #endif 72 73 static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) { 74 const int log_floor = BitsLog2Floor(n); 75 if (n == (n & ~(n - 1))) // zero or a power of two. 76 return log_floor; 77 else 78 return log_floor + 1; 79 } 80 81 // Splitting of distance and length codes into prefixes and 82 // extra bits. The prefixes are encoded with an entropy code 83 // while the extra bits are stored just as normal bits. 84 static WEBP_INLINE void PrefixEncode(int distance, int* const code, 85 int* const extra_bits_count, 86 int* const extra_bits_value) { 87 if (distance > 2) { // Collect the two most significant bits. 88 const int highest_bit = BitsLog2Floor(--distance); 89 const int second_highest_bit = (distance >> (highest_bit - 1)) & 1; 90 *extra_bits_count = highest_bit - 1; 91 *extra_bits_value = distance & ((1 << *extra_bits_count) - 1); 92 *code = 2 * highest_bit + second_highest_bit; 93 } else { 94 *extra_bits_count = 0; 95 *extra_bits_value = 0; 96 *code = (distance == 2) ? 1 : 0; 97 } 98 } 99 100 // ----------------------------------------------------------------------------- 101 // PixOrCopy 102 103 enum Mode { 104 kLiteral, 105 kCacheIdx, 106 kCopy, 107 kNone 108 }; 109 110 typedef struct { 111 // mode as uint8_t to make the memory layout to be exactly 8 bytes. 112 uint8_t mode; 113 uint16_t len; 114 uint32_t argb_or_distance; 115 } PixOrCopy; 116 117 static WEBP_INLINE PixOrCopy PixOrCopyCreateCopy(uint32_t distance, 118 uint16_t len) { 119 PixOrCopy retval; 120 retval.mode = kCopy; 121 retval.argb_or_distance = distance; 122 retval.len = len; 123 return retval; 124 } 125 126 static WEBP_INLINE PixOrCopy PixOrCopyCreateCacheIdx(int idx) { 127 PixOrCopy retval; 128 assert(idx >= 0); 129 assert(idx < (1 << MAX_COLOR_CACHE_BITS)); 130 retval.mode = kCacheIdx; 131 retval.argb_or_distance = idx; 132 retval.len = 1; 133 return retval; 134 } 135 136 static WEBP_INLINE PixOrCopy PixOrCopyCreateLiteral(uint32_t argb) { 137 PixOrCopy retval; 138 retval.mode = kLiteral; 139 retval.argb_or_distance = argb; 140 retval.len = 1; 141 return retval; 142 } 143 144 static WEBP_INLINE int PixOrCopyIsLiteral(const PixOrCopy* const p) { 145 return (p->mode == kLiteral); 146 } 147 148 static WEBP_INLINE int PixOrCopyIsCacheIdx(const PixOrCopy* const p) { 149 return (p->mode == kCacheIdx); 150 } 151 152 static WEBP_INLINE int PixOrCopyIsCopy(const PixOrCopy* const p) { 153 return (p->mode == kCopy); 154 } 155 156 static WEBP_INLINE uint32_t PixOrCopyLiteral(const PixOrCopy* const p, 157 int component) { 158 assert(p->mode == kLiteral); 159 return (p->argb_or_distance >> (component * 8)) & 0xff; 160 } 161 162 static WEBP_INLINE uint32_t PixOrCopyLength(const PixOrCopy* const p) { 163 return p->len; 164 } 165 166 static WEBP_INLINE uint32_t PixOrCopyArgb(const PixOrCopy* const p) { 167 assert(p->mode == kLiteral); 168 return p->argb_or_distance; 169 } 170 171 static WEBP_INLINE uint32_t PixOrCopyCacheIdx(const PixOrCopy* const p) { 172 assert(p->mode == kCacheIdx); 173 assert(p->argb_or_distance < (1U << MAX_COLOR_CACHE_BITS)); 174 return p->argb_or_distance; 175 } 176 177 static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) { 178 assert(p->mode == kCopy); 179 return p->argb_or_distance; 180 } 181 182 // ----------------------------------------------------------------------------- 183 // VP8LBackwardRefs 184 185 typedef struct { 186 PixOrCopy* refs; 187 int size; // currently used 188 int max_size; // maximum capacity 189 } VP8LBackwardRefs; 190 191 // Initialize the object. Must be called first. 'refs' can be NULL. 192 void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs); 193 194 // Release memory and re-initialize the object. 'refs' can be NULL. 195 void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs); 196 197 // Allocate 'max_size' references. Returns false in case of memory error. 198 int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size); 199 200 // ----------------------------------------------------------------------------- 201 // Main entry points 202 203 // Evaluates best possible backward references for specified quality. 204 // Further optimize for 2D locality if use_2d_locality flag is set. 205 int VP8LGetBackwardReferences(int width, int height, 206 const uint32_t* const argb, 207 int quality, int cache_bits, int use_2d_locality, 208 VP8LBackwardRefs* const best); 209 210 // Produce an estimate for a good color cache size for the image. 211 int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb, 212 int xsize, int ysize, 213 int* const best_cache_bits); 214 215 #if defined(__cplusplus) || defined(c_plusplus) 216 } 217 #endif 218 219 #endif // WEBP_ENC_BACKWARD_REFERENCES_H_ 220
