FFmpeg
cabac.c
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1 /*
2  * H.26L/H.264/AVC/JVT/14496-10/... encoder/decoder
3  * Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 /**
23  * @file
24  * Context Adaptive Binary Arithmetic Coder.
25  */
26 
27 #include <string.h>
28 
29 #include "libavutil/common.h"
30 #include "libavutil/mem_internal.h"
31 
32 #include "cabac.h"
33 #include "cabac_functions.h"
34 
35 DECLARE_ASM_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 + 4*64 + 63] = {
36  9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5,
37  4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
38  3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
39  3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
40  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
41  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
42  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
43  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
44  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
45  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
46  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
47  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
48  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
49  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
50  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
51  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
52  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
53  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
54  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
55  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
56  // LPS range
57  -128, -128, -128, -128, -128, -128, 123, 123,
58  116, 116, 111, 111, 105, 105, 100, 100,
59  95, 95, 90, 90, 85, 85, 81, 81,
60  77, 77, 73, 73, 69, 69, 66, 66,
61  62, 62, 59, 59, 56, 56, 53, 53,
62  51, 51, 48, 48, 46, 46, 43, 43,
63  41, 41, 39, 39, 37, 37, 35, 35,
64  33, 33, 32, 32, 30, 30, 29, 29,
65  27, 27, 26, 26, 24, 24, 23, 23,
66  22, 22, 21, 21, 20, 20, 19, 19,
67  18, 18, 17, 17, 16, 16, 15, 15,
68  14, 14, 14, 14, 13, 13, 12, 12,
69  12, 12, 11, 11, 11, 11, 10, 10,
70  10, 10, 9, 9, 9, 9, 8, 8,
71  8, 8, 7, 7, 7, 7, 7, 7,
72  6, 6, 6, 6, 6, 6, 2, 2,
73  -80, -80, -89, -89, -98, -98, -106, -106,
74  -114, -114, -121, -121, -128, -128, 122, 122,
75  116, 116, 110, 110, 104, 104, 99, 99,
76  94, 94, 89, 89, 85, 85, 80, 80,
77  76, 76, 72, 72, 69, 69, 65, 65,
78  62, 62, 59, 59, 56, 56, 53, 53,
79  50, 50, 48, 48, 45, 45, 43, 43,
80  41, 41, 39, 39, 37, 37, 35, 35,
81  33, 33, 31, 31, 30, 30, 28, 28,
82  27, 27, 26, 26, 24, 24, 23, 23,
83  22, 22, 21, 21, 20, 20, 19, 19,
84  18, 18, 17, 17, 16, 16, 15, 15,
85  14, 14, 14, 14, 13, 13, 12, 12,
86  12, 12, 11, 11, 11, 11, 10, 10,
87  9, 9, 9, 9, 9, 9, 8, 8,
88  8, 8, 7, 7, 7, 7, 2, 2,
89  -48, -48, -59, -59, -69, -69, -78, -78,
90  -87, -87, -96, -96, -104, -104, -112, -112,
91  -119, -119, -126, -126, 123, 123, 117, 117,
92  111, 111, 105, 105, 100, 100, 95, 95,
93  90, 90, 86, 86, 81, 81, 77, 77,
94  73, 73, 69, 69, 66, 66, 63, 63,
95  59, 59, 56, 56, 54, 54, 51, 51,
96  48, 48, 46, 46, 43, 43, 41, 41,
97  39, 39, 37, 37, 35, 35, 33, 33,
98  32, 32, 30, 30, 29, 29, 27, 27,
99  26, 26, 25, 25, 23, 23, 22, 22,
100  21, 21, 20, 20, 19, 19, 18, 18,
101  17, 17, 16, 16, 15, 15, 15, 15,
102  14, 14, 13, 13, 12, 12, 12, 12,
103  11, 11, 11, 11, 10, 10, 10, 10,
104  9, 9, 9, 9, 8, 8, 2, 2,
105  -16, -16, -29, -29, -40, -40, -51, -51,
106  -61, -61, -71, -71, -81, -81, -90, -90,
107  -98, -98, -106, -106, -114, -114, -121, -121,
108  -128, -128, 122, 122, 116, 116, 110, 110,
109  104, 104, 99, 99, 94, 94, 89, 89,
110  85, 85, 80, 80, 76, 76, 72, 72,
111  69, 69, 65, 65, 62, 62, 59, 59,
112  56, 56, 53, 53, 50, 50, 48, 48,
113  45, 45, 43, 43, 41, 41, 39, 39,
114  37, 37, 35, 35, 33, 33, 31, 31,
115  30, 30, 28, 28, 27, 27, 25, 25,
116  24, 24, 23, 23, 22, 22, 21, 21,
117  20, 20, 19, 19, 18, 18, 17, 17,
118  16, 16, 15, 15, 14, 14, 14, 14,
119  13, 13, 12, 12, 12, 12, 11, 11,
120  11, 11, 10, 10, 9, 9, 2, 2,
121  // mlps state
122  127, 126, 77, 76, 77, 76, 75, 74,
123  75, 74, 75, 74, 73, 72, 73, 72,
124  73, 72, 71, 70, 71, 70, 71, 70,
125  69, 68, 69, 68, 67, 66, 67, 66,
126  67, 66, 65, 64, 65, 64, 63, 62,
127  61, 60, 61, 60, 61, 60, 59, 58,
128  59, 58, 57, 56, 55, 54, 55, 54,
129  53, 52, 53, 52, 51, 50, 49, 48,
130  49, 48, 47, 46, 45, 44, 45, 44,
131  43, 42, 43, 42, 39, 38, 39, 38,
132  37, 36, 37, 36, 33, 32, 33, 32,
133  31, 30, 31, 30, 27, 26, 27, 26,
134  25, 24, 23, 22, 23, 22, 19, 18,
135  19, 18, 17, 16, 15, 14, 13, 12,
136  11, 10, 9, 8, 9, 8, 5, 4,
137  5, 4, 3, 2, 1, 0, 0, 1,
138  2, 3, 4, 5, 6, 7, 8, 9,
139  10, 11, 12, 13, 14, 15, 16, 17,
140  18, 19, 20, 21, 22, 23, 24, 25,
141  26, 27, 28, 29, 30, 31, 32, 33,
142  34, 35, 36, 37, 38, 39, 40, 41,
143  42, 43, 44, 45, 46, 47, 48, 49,
144  50, 51, 52, 53, 54, 55, 56, 57,
145  58, 59, 60, 61, 62, 63, 64, 65,
146  66, 67, 68, 69, 70, 71, 72, 73,
147  74, 75, 76, 77, 78, 79, 80, 81,
148  82, 83, 84, 85, 86, 87, 88, 89,
149  90, 91, 92, 93, 94, 95, 96, 97,
150  98, 99, 100, 101, 102, 103, 104, 105,
151  106, 107, 108, 109, 110, 111, 112, 113,
152  114, 115, 116, 117, 118, 119, 120, 121,
153  122, 123, 124, 125, 124, 125, 126, 127,
154  // last_coeff_flag_offset_8x8
155  0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
156  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
157  3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
158  5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8
159 };
160 
161 /**
162  *
163  * @param buf_size size of buf in bits
164  */
165 int ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size){
166  c->bytestream_start=
167  c->bytestream= buf;
168  c->bytestream_end= buf + buf_size;
169 
170 #if CABAC_BITS == 16
171  c->low = (*c->bytestream++)<<18;
172  c->low+= (*c->bytestream++)<<10;
173  // Keep our fetches on a 2-byte boundary as this should avoid ever having to
174  // do unaligned loads if the compiler (or asm) optimises the double byte
175  // load into a single instruction
176  if(((uintptr_t)c->bytestream & 1) == 0) {
177  c->low += (1 << 9);
178  }
179  else {
180  c->low += ((*c->bytestream++) << 2) + 2;
181  }
182 #else
183  c->low = (*c->bytestream++)<<10;
184  c->low+= ((*c->bytestream++)<<2) + 2;
185 #endif
186  c->range= 0x1FE;
187  if ((c->range<<(CABAC_BITS+1)) < c->low)
188  return AVERROR_INVALIDDATA;
189  return 0;
190 }
cabac.h
mem_internal.h
ff_h264_cabac_tables
const uint8_t ff_h264_cabac_tables[512+4 *2 *64+4 *64+63]
DECLARE_ASM_ALIGNED
DECLARE_ASM_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512+4 *2 *64+4 *64+63]
c
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
ff_init_cabac_decoder
int ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size)
Definition: cabac.c:165
common.h
cabac_functions.h
AVERROR_INVALIDDATA
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:59
CABAC_BITS
#define CABAC_BITS
Definition: cabac.h:38
CABACContext
Definition: cabac.h:41
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