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
24extern "C" {
25#endif
26
27//------------------------------------------------------------------------------
28// Decoding
29
30// color mapping related functions.
31static WEBP_INLINE uint32_t VP8GetARGBIndex(uint32_t idx) {
32 return (idx >> 8) & 0xff;
33}
34
35static WEBP_INLINE uint8_t VP8GetAlphaIndex(uint8_t idx) {
36 return idx;
37}
38
39static WEBP_INLINE uint32_t VP8GetARGBValue(uint32_t val) {
40 return val;
41}
42
43static 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'.
51static 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.
57static 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
78extern const float kLog2Table[LOG_LOOKUP_IDX_MAX];
79extern const float kSLog2Table[LOG_LOOKUP_IDX_MAX];
80typedef float (*VP8LFastLog2SlowFunc)(uint32_t v);
81
82extern VP8LFastLog2SlowFunc VP8LFastLog2Slow;
83extern VP8LFastLog2SlowFunc VP8LFastSLog2Slow;
84
85static 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.
89static 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.
99static 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
107static 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
118typedef struct {
119 int8_t code_;
120 int8_t extra_bits_;
121} VP8LPrefixCode;
122
123// These tables are derived using VP8LPrefixEncodeNoLUT.
124extern const VP8LPrefixCode kPrefixEncodeCode[PREFIX_LOOKUP_IDX_MAX];
125extern const uint8_t kPrefixEncodeExtraBitsValue[PREFIX_LOOKUP_IDX_MAX];
126static 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
137static 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.
151static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE
152uint32_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.
159static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE
160uint32_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) \
177static 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