FFmpeg
cabac.c
Go to the documentation of this file.
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 "libavutil/error.h"
28 #include "libavutil/mem_internal.h"
29 
30 #include "cabac.h"
31 
32 DECLARE_ASM_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 + 4*64 + 63] = {
33  9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5,
34  4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
35  3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
36  3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
37  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
38  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
39  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
40  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
41  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,
42  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,
43  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,
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  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,
46  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,
47  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,
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  // LPS range
54  -128, -128, -128, -128, -128, -128, 123, 123,
55  116, 116, 111, 111, 105, 105, 100, 100,
56  95, 95, 90, 90, 85, 85, 81, 81,
57  77, 77, 73, 73, 69, 69, 66, 66,
58  62, 62, 59, 59, 56, 56, 53, 53,
59  51, 51, 48, 48, 46, 46, 43, 43,
60  41, 41, 39, 39, 37, 37, 35, 35,
61  33, 33, 32, 32, 30, 30, 29, 29,
62  27, 27, 26, 26, 24, 24, 23, 23,
63  22, 22, 21, 21, 20, 20, 19, 19,
64  18, 18, 17, 17, 16, 16, 15, 15,
65  14, 14, 14, 14, 13, 13, 12, 12,
66  12, 12, 11, 11, 11, 11, 10, 10,
67  10, 10, 9, 9, 9, 9, 8, 8,
68  8, 8, 7, 7, 7, 7, 7, 7,
69  6, 6, 6, 6, 6, 6, 2, 2,
70  -80, -80, -89, -89, -98, -98, -106, -106,
71  -114, -114, -121, -121, -128, -128, 122, 122,
72  116, 116, 110, 110, 104, 104, 99, 99,
73  94, 94, 89, 89, 85, 85, 80, 80,
74  76, 76, 72, 72, 69, 69, 65, 65,
75  62, 62, 59, 59, 56, 56, 53, 53,
76  50, 50, 48, 48, 45, 45, 43, 43,
77  41, 41, 39, 39, 37, 37, 35, 35,
78  33, 33, 31, 31, 30, 30, 28, 28,
79  27, 27, 26, 26, 24, 24, 23, 23,
80  22, 22, 21, 21, 20, 20, 19, 19,
81  18, 18, 17, 17, 16, 16, 15, 15,
82  14, 14, 14, 14, 13, 13, 12, 12,
83  12, 12, 11, 11, 11, 11, 10, 10,
84  9, 9, 9, 9, 9, 9, 8, 8,
85  8, 8, 7, 7, 7, 7, 2, 2,
86  -48, -48, -59, -59, -69, -69, -78, -78,
87  -87, -87, -96, -96, -104, -104, -112, -112,
88  -119, -119, -126, -126, 123, 123, 117, 117,
89  111, 111, 105, 105, 100, 100, 95, 95,
90  90, 90, 86, 86, 81, 81, 77, 77,
91  73, 73, 69, 69, 66, 66, 63, 63,
92  59, 59, 56, 56, 54, 54, 51, 51,
93  48, 48, 46, 46, 43, 43, 41, 41,
94  39, 39, 37, 37, 35, 35, 33, 33,
95  32, 32, 30, 30, 29, 29, 27, 27,
96  26, 26, 25, 25, 23, 23, 22, 22,
97  21, 21, 20, 20, 19, 19, 18, 18,
98  17, 17, 16, 16, 15, 15, 15, 15,
99  14, 14, 13, 13, 12, 12, 12, 12,
100  11, 11, 11, 11, 10, 10, 10, 10,
101  9, 9, 9, 9, 8, 8, 2, 2,
102  -16, -16, -29, -29, -40, -40, -51, -51,
103  -61, -61, -71, -71, -81, -81, -90, -90,
104  -98, -98, -106, -106, -114, -114, -121, -121,
105  -128, -128, 122, 122, 116, 116, 110, 110,
106  104, 104, 99, 99, 94, 94, 89, 89,
107  85, 85, 80, 80, 76, 76, 72, 72,
108  69, 69, 65, 65, 62, 62, 59, 59,
109  56, 56, 53, 53, 50, 50, 48, 48,
110  45, 45, 43, 43, 41, 41, 39, 39,
111  37, 37, 35, 35, 33, 33, 31, 31,
112  30, 30, 28, 28, 27, 27, 25, 25,
113  24, 24, 23, 23, 22, 22, 21, 21,
114  20, 20, 19, 19, 18, 18, 17, 17,
115  16, 16, 15, 15, 14, 14, 14, 14,
116  13, 13, 12, 12, 12, 12, 11, 11,
117  11, 11, 10, 10, 9, 9, 2, 2,
118  // mlps state
119  127, 126, 77, 76, 77, 76, 75, 74,
120  75, 74, 75, 74, 73, 72, 73, 72,
121  73, 72, 71, 70, 71, 70, 71, 70,
122  69, 68, 69, 68, 67, 66, 67, 66,
123  67, 66, 65, 64, 65, 64, 63, 62,
124  61, 60, 61, 60, 61, 60, 59, 58,
125  59, 58, 57, 56, 55, 54, 55, 54,
126  53, 52, 53, 52, 51, 50, 49, 48,
127  49, 48, 47, 46, 45, 44, 45, 44,
128  43, 42, 43, 42, 39, 38, 39, 38,
129  37, 36, 37, 36, 33, 32, 33, 32,
130  31, 30, 31, 30, 27, 26, 27, 26,
131  25, 24, 23, 22, 23, 22, 19, 18,
132  19, 18, 17, 16, 15, 14, 13, 12,
133  11, 10, 9, 8, 9, 8, 5, 4,
134  5, 4, 3, 2, 1, 0, 0, 1,
135  2, 3, 4, 5, 6, 7, 8, 9,
136  10, 11, 12, 13, 14, 15, 16, 17,
137  18, 19, 20, 21, 22, 23, 24, 25,
138  26, 27, 28, 29, 30, 31, 32, 33,
139  34, 35, 36, 37, 38, 39, 40, 41,
140  42, 43, 44, 45, 46, 47, 48, 49,
141  50, 51, 52, 53, 54, 55, 56, 57,
142  58, 59, 60, 61, 62, 63, 64, 65,
143  66, 67, 68, 69, 70, 71, 72, 73,
144  74, 75, 76, 77, 78, 79, 80, 81,
145  82, 83, 84, 85, 86, 87, 88, 89,
146  90, 91, 92, 93, 94, 95, 96, 97,
147  98, 99, 100, 101, 102, 103, 104, 105,
148  106, 107, 108, 109, 110, 111, 112, 113,
149  114, 115, 116, 117, 118, 119, 120, 121,
150  122, 123, 124, 125, 124, 125, 126, 127,
151  // last_coeff_flag_offset_8x8
152  0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
153  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
154  3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
155  5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8
156 };
157 
158 /**
159  *
160  * @param buf_size size of buf in bits
161  */
162 int ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size){
163  c->bytestream_start=
164  c->bytestream= buf;
165  c->bytestream_end= buf + buf_size;
166 
167 #if CABAC_BITS == 16
168  c->low = (*c->bytestream++)<<18;
169  c->low+= (*c->bytestream++)<<10;
170  // Keep our fetches on a 2-byte boundary as this should avoid ever having to
171  // do unaligned loads if the compiler (or asm) optimises the double byte
172  // load into a single instruction
173  if(((uintptr_t)c->bytestream & 1) == 0) {
174  c->low += (1 << 9);
175  }
176  else {
177  c->low += ((*c->bytestream++) << 2) + 2;
178  }
179 #else
180  c->low = (*c->bytestream++)<<10;
181  c->low+= ((*c->bytestream++)<<2) + 2;
182 #endif
183  c->range= 0x1FE;
184  if ((c->range<<(CABAC_BITS+1)) < c->low)
185  return AVERROR_INVALIDDATA;
186  return 0;
187 }
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
error.h
ff_init_cabac_decoder
int ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size)
Definition: cabac.c:162
AVERROR_INVALIDDATA
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:61
CABAC_BITS
#define CABAC_BITS
Definition: cabac.h:38
CABACContext
Definition: cabac.h:41
Generated on Tue Feb 7 2023 19:21:19 for FFmpeg by   doxygen 1.8.17