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  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)             \
189static 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