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      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