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 // Author: Jyrki Alakuijala (jyrki@google.com)
11 //
12
13 #ifndef WEBP_ENC_BACKWARD_REFERENCES_H_
14 #define WEBP_ENC_BACKWARD_REFERENCES_H_
15
16 #include <assert.h>
17 #include <stdlib.h>
18 #include "webp/types.h"
19 #include "webp/format_constants.h"
20
21 #if defined(__cplusplus) || defined(c_plusplus)
22 extern "C" {
23 #endif
24
25 // The spec allows 11, we use 9 bits to reduce memory consumption in encoding.
26 // Having 9 instead of 11 only removes about 0.25 % of compression density.
27 #define MAX_COLOR_CACHE_BITS 9
28
29 // Max ever number of codes we'll use:
30 #define PIX_OR_COPY_CODES_MAX \
31 (NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS))
32
33 // -----------------------------------------------------------------------------
34 // PrefixEncode()
35
36 // use GNU builtins where available.
37 #if defined(__GNUC__) && \
38 ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
BitsLog2Floor(uint32_t n)39 static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
40 assert(n != 0);
41 return 31 ^ __builtin_clz(n);
42 }
43 #elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86))
44 #include <intrin.h>
45 #pragma intrinsic(_BitScanReverse)
46
47 static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
48 unsigned long first_set_bit;
49 assert(n != 0);
50 _BitScanReverse(&first_set_bit, n);
51 return first_set_bit;
52 }
53 #else
54 // Returns (int)floor(log2(n)). n must be > 0.
55 static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
56 int log = 0;
57 uint32_t value = n;
58 int i;
59
60 assert(n != 0);
61 for (i = 4; i >= 0; --i) {
62 const int shift = (1 << i);
63 const uint32_t x = value >> shift;
64 if (x != 0) {
65 value = x;
66 log += shift;
67 }
68 }
69 return log;
70 }
71 #endif
72
VP8LBitsLog2Ceiling(uint32_t n)73 static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) {
74 const int log_floor = BitsLog2Floor(n);
75 if (n == (n & ~(n - 1))) // zero or a power of two.
76 return log_floor;
77 else
78 return log_floor + 1;
79 }
80
81 // Splitting of distance and length codes into prefixes and
82 // extra bits. The prefixes are encoded with an entropy code
83 // while the extra bits are stored just as normal bits.
PrefixEncode(int distance,int * const code,int * const extra_bits_count,int * const extra_bits_value)84 static WEBP_INLINE void PrefixEncode(int distance, int* const code,
85 int* const extra_bits_count,
86 int* const extra_bits_value) {
87 if (distance > 2) { // Collect the two most significant bits.
88 const int highest_bit = BitsLog2Floor(--distance);
89 const int second_highest_bit = (distance >> (highest_bit - 1)) & 1;
90 *extra_bits_count = highest_bit - 1;
91 *extra_bits_value = distance & ((1 << *extra_bits_count) - 1);
92 *code = 2 * highest_bit + second_highest_bit;
93 } else {
94 *extra_bits_count = 0;
95 *extra_bits_value = 0;
96 *code = (distance == 2) ? 1 : 0;
97 }
98 }
99
100 // -----------------------------------------------------------------------------
101 // PixOrCopy
102
103 enum Mode {
104 kLiteral,
105 kCacheIdx,
106 kCopy,
107 kNone
108 };
109
110 typedef struct {
111 // mode as uint8_t to make the memory layout to be exactly 8 bytes.
112 uint8_t mode;
113 uint16_t len;
114 uint32_t argb_or_distance;
115 } PixOrCopy;
116
PixOrCopyCreateCopy(uint32_t distance,uint16_t len)117 static WEBP_INLINE PixOrCopy PixOrCopyCreateCopy(uint32_t distance,
118 uint16_t len) {
119 PixOrCopy retval;
120 retval.mode = kCopy;
121 retval.argb_or_distance = distance;
122 retval.len = len;
123 return retval;
124 }
125
PixOrCopyCreateCacheIdx(int idx)126 static WEBP_INLINE PixOrCopy PixOrCopyCreateCacheIdx(int idx) {
127 PixOrCopy retval;
128 assert(idx >= 0);
129 assert(idx < (1 << MAX_COLOR_CACHE_BITS));
130 retval.mode = kCacheIdx;
131 retval.argb_or_distance = idx;
132 retval.len = 1;
133 return retval;
134 }
135
PixOrCopyCreateLiteral(uint32_t argb)136 static WEBP_INLINE PixOrCopy PixOrCopyCreateLiteral(uint32_t argb) {
137 PixOrCopy retval;
138 retval.mode = kLiteral;
139 retval.argb_or_distance = argb;
140 retval.len = 1;
141 return retval;
142 }
143
PixOrCopyIsLiteral(const PixOrCopy * const p)144 static WEBP_INLINE int PixOrCopyIsLiteral(const PixOrCopy* const p) {
145 return (p->mode == kLiteral);
146 }
147
PixOrCopyIsCacheIdx(const PixOrCopy * const p)148 static WEBP_INLINE int PixOrCopyIsCacheIdx(const PixOrCopy* const p) {
149 return (p->mode == kCacheIdx);
150 }
151
PixOrCopyIsCopy(const PixOrCopy * const p)152 static WEBP_INLINE int PixOrCopyIsCopy(const PixOrCopy* const p) {
153 return (p->mode == kCopy);
154 }
155
PixOrCopyLiteral(const PixOrCopy * const p,int component)156 static WEBP_INLINE uint32_t PixOrCopyLiteral(const PixOrCopy* const p,
157 int component) {
158 assert(p->mode == kLiteral);
159 return (p->argb_or_distance >> (component * 8)) & 0xff;
160 }
161
PixOrCopyLength(const PixOrCopy * const p)162 static WEBP_INLINE uint32_t PixOrCopyLength(const PixOrCopy* const p) {
163 return p->len;
164 }
165
PixOrCopyArgb(const PixOrCopy * const p)166 static WEBP_INLINE uint32_t PixOrCopyArgb(const PixOrCopy* const p) {
167 assert(p->mode == kLiteral);
168 return p->argb_or_distance;
169 }
170
PixOrCopyCacheIdx(const PixOrCopy * const p)171 static WEBP_INLINE uint32_t PixOrCopyCacheIdx(const PixOrCopy* const p) {
172 assert(p->mode == kCacheIdx);
173 assert(p->argb_or_distance < (1U << MAX_COLOR_CACHE_BITS));
174 return p->argb_or_distance;
175 }
176
PixOrCopyDistance(const PixOrCopy * const p)177 static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) {
178 assert(p->mode == kCopy);
179 return p->argb_or_distance;
180 }
181
182 // -----------------------------------------------------------------------------
183 // VP8LBackwardRefs
184
185 typedef struct {
186 PixOrCopy* refs;
187 int size; // currently used
188 int max_size; // maximum capacity
189 } VP8LBackwardRefs;
190
191 // Initialize the object. Must be called first. 'refs' can be NULL.
192 void VP8LInitBackwardRefs(VP8LBackwardRefs* const refs);
193
194 // Release memory and re-initialize the object. 'refs' can be NULL.
195 void VP8LClearBackwardRefs(VP8LBackwardRefs* const refs);
196
197 // Allocate 'max_size' references. Returns false in case of memory error.
198 int VP8LBackwardRefsAlloc(VP8LBackwardRefs* const refs, int max_size);
199
200 // -----------------------------------------------------------------------------
201 // Main entry points
202
203 // Evaluates best possible backward references for specified quality.
204 // Further optimize for 2D locality if use_2d_locality flag is set.
205 int VP8LGetBackwardReferences(int width, int height,
206 const uint32_t* const argb,
207 int quality, int cache_bits, int use_2d_locality,
208 VP8LBackwardRefs* const best);
209
210 // Produce an estimate for a good color cache size for the image.
211 int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
212 int xsize, int ysize,
213 int* const best_cache_bits);
214
215 #if defined(__cplusplus) || defined(c_plusplus)
216 }
217 #endif
218
219 #endif // WEBP_ENC_BACKWARD_REFERENCES_H_
220