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 // Image transforms and color space conversion methods for lossless decoder. 11 // 12 // Authors: Vikas Arora (vikaas.arora (at) gmail.com) 13 // Jyrki Alakuijala (jyrki (at) google.com) 14 // Vincent Rabaud (vrabaud (at) google.com) 15 16 #ifndef WEBP_DSP_LOSSLESS_COMMON_H_ 17 #define WEBP_DSP_LOSSLESS_COMMON_H_ 18 19 #include "src/webp/types.h" 20 21 #include "src/utils/utils.h" 22 23 #ifdef __cplusplus 24 extern "C" { 25 #endif 26 27 //------------------------------------------------------------------------------ 28 // Decoding 29 30 // color mapping related functions. 31 static WEBP_INLINE uint32_t VP8GetARGBIndex(uint32_t idx) { 32 return (idx >> 8) & 0xff; 33 } 34 35 static WEBP_INLINE uint8_t VP8GetAlphaIndex(uint8_t idx) { 36 return idx; 37 } 38 39 static WEBP_INLINE uint32_t VP8GetARGBValue(uint32_t val) { 40 return val; 41 } 42 43 static WEBP_INLINE uint8_t VP8GetAlphaValue(uint32_t val) { 44 return (val >> 8) & 0xff; 45 } 46 47 //------------------------------------------------------------------------------ 48 // Misc methods. 49 50 // Computes sampled size of 'size' when sampling using 'sampling bits'. 51 static WEBP_INLINE uint32_t VP8LSubSampleSize(uint32_t size, 52 uint32_t sampling_bits) { 53 return (size + (1 << sampling_bits) - 1) >> sampling_bits; 54 } 55 56 // Converts near lossless quality into max number of bits shaved off. 57 static WEBP_INLINE int VP8LNearLosslessBits(int near_lossless_quality) { 58 // 100 -> 0 59 // 80..99 -> 1 60 // 60..79 -> 2 61 // 40..59 -> 3 62 // 20..39 -> 4 63 // 0..19 -> 5 64 return 5 - near_lossless_quality / 20; 65 } 66 67 // ----------------------------------------------------------------------------- 68 // Faster logarithm for integers. Small values use a look-up table. 69 70 // The threshold till approximate version of log_2 can be used. 71 // Practically, we can get rid of the call to log() as the two values match to 72 // very high degree (the ratio of these two is 0.99999x). 73 // Keeping a high threshold for now. 74 #define APPROX_LOG_WITH_CORRECTION_MAX 65536 75 #define APPROX_LOG_MAX 4096 76 #define LOG_2_RECIPROCAL 1.44269504088896338700465094007086 77 #define LOG_LOOKUP_IDX_MAX 256 78 extern const float kLog2Table[LOG_LOOKUP_IDX_MAX]; 79 extern const float kSLog2Table[LOG_LOOKUP_IDX_MAX]; 80 typedef float (*VP8LFastLog2SlowFunc)(uint32_t v); 81 82 extern VP8LFastLog2SlowFunc VP8LFastLog2Slow; 83 extern VP8LFastLog2SlowFunc VP8LFastSLog2Slow; 84 85 static WEBP_INLINE float VP8LFastLog2(uint32_t v) { 86 return (v < LOG_LOOKUP_IDX_MAX) ? kLog2Table[v] : VP8LFastLog2Slow(v); 87 } 88 // Fast calculation of v * log2(v) for integer input. 89 static WEBP_INLINE float VP8LFastSLog2(uint32_t v) { 90 return (v < LOG_LOOKUP_IDX_MAX) ? kSLog2Table[v] : VP8LFastSLog2Slow(v); 91 } 92 93 // ----------------------------------------------------------------------------- 94 // PrefixEncode() 95 96 // Splitting of distance and length codes into prefixes and 97 // extra bits. The prefixes are encoded with an entropy code 98 // while the extra bits are stored just as normal bits. 99 static WEBP_INLINE void VP8LPrefixEncodeBitsNoLUT(int distance, int* const code, 100 int* const extra_bits) { 101 const int highest_bit = BitsLog2Floor(--distance); 102 const int second_highest_bit = (distance >> (highest_bit - 1)) & 1; 103 *extra_bits = highest_bit - 1; 104 *code = 2 * highest_bit + second_highest_bit; 105 } 106 107 static WEBP_INLINE void VP8LPrefixEncodeNoLUT(int distance, int* const code, 108 int* const extra_bits, 109 int* const extra_bits_value) { 110 const int highest_bit = BitsLog2Floor(--distance); 111 const int second_highest_bit = (distance >> (highest_bit - 1)) & 1; 112 *extra_bits = highest_bit - 1; 113 *extra_bits_value = distance & ((1 << *extra_bits) - 1); 114 *code = 2 * highest_bit + second_highest_bit; 115 } 116 117 #define PREFIX_LOOKUP_IDX_MAX 512 118 typedef struct { 119 int8_t code_; 120 int8_t extra_bits_; 121 } VP8LPrefixCode; 122 123 // These tables are derived using VP8LPrefixEncodeNoLUT. 124 extern const VP8LPrefixCode kPrefixEncodeCode[PREFIX_LOOKUP_IDX_MAX]; 125 extern const uint8_t kPrefixEncodeExtraBitsValue[PREFIX_LOOKUP_IDX_MAX]; 126 static WEBP_INLINE void VP8LPrefixEncodeBits(int distance, int* const code, 127 int* const extra_bits) { 128 if (distance < PREFIX_LOOKUP_IDX_MAX) { 129 const VP8LPrefixCode prefix_code = kPrefixEncodeCode[distance]; 130 *code = prefix_code.code_; 131 *extra_bits = prefix_code.extra_bits_; 132 } else { 133 VP8LPrefixEncodeBitsNoLUT(distance, code, extra_bits); 134 } 135 } 136 137 static WEBP_INLINE void VP8LPrefixEncode(int distance, int* const code, 138 int* const extra_bits, 139 int* const extra_bits_value) { 140 if (distance < PREFIX_LOOKUP_IDX_MAX) { 141 const VP8LPrefixCode prefix_code = kPrefixEncodeCode[distance]; 142 *code = prefix_code.code_; 143 *extra_bits = prefix_code.extra_bits_; 144 *extra_bits_value = kPrefixEncodeExtraBitsValue[distance]; 145 } else { 146 VP8LPrefixEncodeNoLUT(distance, code, extra_bits, extra_bits_value); 147 } 148 } 149 150 // Sum of each component, mod 256. 151 static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE 152 uint32_t VP8LAddPixels(uint32_t a, uint32_t b) { 153 const uint32_t alpha_and_green = (a & 0xff00ff00u) + (b & 0xff00ff00u); 154 const uint32_t red_and_blue = (a & 0x00ff00ffu) + (b & 0x00ff00ffu); 155 return (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu); 156 } 157 158 // Difference of each component, mod 256. 159 static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE 160 uint32_t VP8LSubPixels(uint32_t a, uint32_t b) { 161 const uint32_t alpha_and_green = 162 0x00ff00ffu + (a & 0xff00ff00u) - (b & 0xff00ff00u); 163 const uint32_t red_and_blue = 164 0xff00ff00u + (a & 0x00ff00ffu) - (b & 0x00ff00ffu); 165 return (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu); 166 } 167 168 //------------------------------------------------------------------------------ 169 // Transform-related functions use din both encoding and decoding. 170 171 // Macros used to create a batch predictor that iteratively uses a 172 // one-pixel predictor. 173 174 // The predictor is added to the output pixel (which 175 // is therefore considered as a residual) to get the final prediction. 176 #define GENERATE_PREDICTOR_ADD(PREDICTOR, PREDICTOR_ADD) \ 177 static void PREDICTOR_ADD(const uint32_t* in, const uint32_t* upper, \ 178 int num_pixels, uint32_t* out) { \ 179 int x; \ 180 for (x = 0; x < num_pixels; ++x) { \ 181 const uint32_t pred = (PREDICTOR)(out[x - 1], upper + x); \ 182 out[x] = VP8LAddPixels(in[x], pred); \ 183 } \ 184 } 185 186 // It subtracts the prediction from the input pixel and stores the residual 187 // in the output pixel. 188 #define GENERATE_PREDICTOR_SUB(PREDICTOR, PREDICTOR_SUB) \ 189 static void PREDICTOR_SUB(const uint32_t* in, const uint32_t* upper, \ 190 int num_pixels, uint32_t* out) { \ 191 int x; \ 192 for (x = 0; x < num_pixels; ++x) { \ 193 const uint32_t pred = (PREDICTOR)(in[x - 1], upper + x); \ 194 out[x] = VP8LSubPixels(in[x], pred); \ 195 } \ 196 } 197 198 #ifdef __cplusplus 199 } // extern "C" 200 #endif 201 202 #endif // WEBP_DSP_LOSSLESS_COMMON_H_ 203