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@gmail.com)
13 //          Jyrki Alakuijala (jyrki@google.com)
14 //          Vincent Rabaud (vrabaud@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.
VP8GetARGBIndex(uint32_t idx)31 static WEBP_INLINE uint32_t VP8GetARGBIndex(uint32_t idx) {
32   return (idx >> 8) & 0xff;
33 }
34 
VP8GetAlphaIndex(uint8_t idx)35 static WEBP_INLINE uint8_t VP8GetAlphaIndex(uint8_t idx) {
36   return idx;
37 }
38 
VP8GetARGBValue(uint32_t val)39 static WEBP_INLINE uint32_t VP8GetARGBValue(uint32_t val) {
40   return val;
41 }
42 
VP8GetAlphaValue(uint32_t val)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'.
VP8LSubSampleSize(uint32_t size,uint32_t 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.
VP8LNearLosslessBits(int near_lossless_quality)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 
VP8LFastLog2(uint32_t v)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.
VP8LFastSLog2(uint32_t v)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.
VP8LPrefixEncodeBitsNoLUT(int distance,int * const code,int * const extra_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 
VP8LPrefixEncodeNoLUT(int distance,int * const code,int * const extra_bits,int * const extra_bits_value)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];
VP8LPrefixEncodeBits(int distance,int * const code,int * const extra_bits)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 
VP8LPrefixEncode(int distance,int * const code,int * const extra_bits,int * const extra_bits_value)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
VP8LAddPixels(uint32_t a,uint32_t b)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
VP8LSubPixels(uint32_t a,uint32_t b)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   assert(upper != NULL);                                             \
181   for (x = 0; x < num_pixels; ++x) {                                 \
182     const uint32_t pred = (PREDICTOR)(out[x - 1], upper + x);        \
183     out[x] = VP8LAddPixels(in[x], pred);                             \
184   }                                                                  \
185 }
186 
187 #ifdef __cplusplus
188 }    // extern "C"
189 #endif
190 
191 #endif  // WEBP_DSP_LOSSLESS_COMMON_H_
192