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 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