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 
31 #include "cabac.h"
32 #include "cabac_functions.h"
33 
34 DECLARE_ASM_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 + 4*64 + 63] = {
35  9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5,
36  4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
37  3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
38  3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
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  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  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  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  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  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  // LPS range
56  -128, -128, -128, -128, -128, -128, 123, 123,
57  116, 116, 111, 111, 105, 105, 100, 100,
58  95, 95, 90, 90, 85, 85, 81, 81,
59  77, 77, 73, 73, 69, 69, 66, 66,
60  62, 62, 59, 59, 56, 56, 53, 53,
61  51, 51, 48, 48, 46, 46, 43, 43,
62  41, 41, 39, 39, 37, 37, 35, 35,
63  33, 33, 32, 32, 30, 30, 29, 29,
64  27, 27, 26, 26, 24, 24, 23, 23,
65  22, 22, 21, 21, 20, 20, 19, 19,
66  18, 18, 17, 17, 16, 16, 15, 15,
67  14, 14, 14, 14, 13, 13, 12, 12,
68  12, 12, 11, 11, 11, 11, 10, 10,
69  10, 10, 9, 9, 9, 9, 8, 8,
70  8, 8, 7, 7, 7, 7, 7, 7,
71  6, 6, 6, 6, 6, 6, 2, 2,
72  -80, -80, -89, -89, -98, -98, -106, -106,
73  -114, -114, -121, -121, -128, -128, 122, 122,
74  116, 116, 110, 110, 104, 104, 99, 99,
75  94, 94, 89, 89, 85, 85, 80, 80,
76  76, 76, 72, 72, 69, 69, 65, 65,
77  62, 62, 59, 59, 56, 56, 53, 53,
78  50, 50, 48, 48, 45, 45, 43, 43,
79  41, 41, 39, 39, 37, 37, 35, 35,
80  33, 33, 31, 31, 30, 30, 28, 28,
81  27, 27, 26, 26, 24, 24, 23, 23,
82  22, 22, 21, 21, 20, 20, 19, 19,
83  18, 18, 17, 17, 16, 16, 15, 15,
84  14, 14, 14, 14, 13, 13, 12, 12,
85  12, 12, 11, 11, 11, 11, 10, 10,
86  9, 9, 9, 9, 9, 9, 8, 8,
87  8, 8, 7, 7, 7, 7, 2, 2,
88  -48, -48, -59, -59, -69, -69, -78, -78,
89  -87, -87, -96, -96, -104, -104, -112, -112,
90  -119, -119, -126, -126, 123, 123, 117, 117,
91  111, 111, 105, 105, 100, 100, 95, 95,
92  90, 90, 86, 86, 81, 81, 77, 77,
93  73, 73, 69, 69, 66, 66, 63, 63,
94  59, 59, 56, 56, 54, 54, 51, 51,
95  48, 48, 46, 46, 43, 43, 41, 41,
96  39, 39, 37, 37, 35, 35, 33, 33,
97  32, 32, 30, 30, 29, 29, 27, 27,
98  26, 26, 25, 25, 23, 23, 22, 22,
99  21, 21, 20, 20, 19, 19, 18, 18,
100  17, 17, 16, 16, 15, 15, 15, 15,
101  14, 14, 13, 13, 12, 12, 12, 12,
102  11, 11, 11, 11, 10, 10, 10, 10,
103  9, 9, 9, 9, 8, 8, 2, 2,
104  -16, -16, -29, -29, -40, -40, -51, -51,
105  -61, -61, -71, -71, -81, -81, -90, -90,
106  -98, -98, -106, -106, -114, -114, -121, -121,
107  -128, -128, 122, 122, 116, 116, 110, 110,
108  104, 104, 99, 99, 94, 94, 89, 89,
109  85, 85, 80, 80, 76, 76, 72, 72,
110  69, 69, 65, 65, 62, 62, 59, 59,
111  56, 56, 53, 53, 50, 50, 48, 48,
112  45, 45, 43, 43, 41, 41, 39, 39,
113  37, 37, 35, 35, 33, 33, 31, 31,
114  30, 30, 28, 28, 27, 27, 25, 25,
115  24, 24, 23, 23, 22, 22, 21, 21,
116  20, 20, 19, 19, 18, 18, 17, 17,
117  16, 16, 15, 15, 14, 14, 14, 14,
118  13, 13, 12, 12, 12, 12, 11, 11,
119  11, 11, 10, 10, 9, 9, 2, 2,
120  // mlps state
121  127, 126, 77, 76, 77, 76, 75, 74,
122  75, 74, 75, 74, 73, 72, 73, 72,
123  73, 72, 71, 70, 71, 70, 71, 70,
124  69, 68, 69, 68, 67, 66, 67, 66,
125  67, 66, 65, 64, 65, 64, 63, 62,
126  61, 60, 61, 60, 61, 60, 59, 58,
127  59, 58, 57, 56, 55, 54, 55, 54,
128  53, 52, 53, 52, 51, 50, 49, 48,
129  49, 48, 47, 46, 45, 44, 45, 44,
130  43, 42, 43, 42, 39, 38, 39, 38,
131  37, 36, 37, 36, 33, 32, 33, 32,
132  31, 30, 31, 30, 27, 26, 27, 26,
133  25, 24, 23, 22, 23, 22, 19, 18,
134  19, 18, 17, 16, 15, 14, 13, 12,
135  11, 10, 9, 8, 9, 8, 5, 4,
136  5, 4, 3, 2, 1, 0, 0, 1,
137  2, 3, 4, 5, 6, 7, 8, 9,
138  10, 11, 12, 13, 14, 15, 16, 17,
139  18, 19, 20, 21, 22, 23, 24, 25,
140  26, 27, 28, 29, 30, 31, 32, 33,
141  34, 35, 36, 37, 38, 39, 40, 41,
142  42, 43, 44, 45, 46, 47, 48, 49,
143  50, 51, 52, 53, 54, 55, 56, 57,
144  58, 59, 60, 61, 62, 63, 64, 65,
145  66, 67, 68, 69, 70, 71, 72, 73,
146  74, 75, 76, 77, 78, 79, 80, 81,
147  82, 83, 84, 85, 86, 87, 88, 89,
148  90, 91, 92, 93, 94, 95, 96, 97,
149  98, 99, 100, 101, 102, 103, 104, 105,
150  106, 107, 108, 109, 110, 111, 112, 113,
151  114, 115, 116, 117, 118, 119, 120, 121,
152  122, 123, 124, 125, 124, 125, 126, 127,
153  // last_coeff_flag_offset_8x8
154  0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
155  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
156  3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
157  5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8
158 };
159 
160 /**
161  * @param buf_size size of buf in bits
162  */
163 void ff_init_cabac_encoder(CABACContext *c, uint8_t *buf, int buf_size){
164  init_put_bits(&c->pb, buf, buf_size);
165 
166  c->low= 0;
167  c->range= 0x1FE;
168  c->outstanding_count= 0;
169  c->pb.bit_left++; //avoids firstBitFlag
170 }
171 
172 /**
173  *
174  * @param buf_size size of buf in bits
175  */
176 int ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size){
177  c->bytestream_start=
178  c->bytestream= buf;
179  c->bytestream_end= buf + buf_size;
180 
181 #if CABAC_BITS == 16
182  c->low = (*c->bytestream++)<<18;
183  c->low+= (*c->bytestream++)<<10;
184  // Keep our fetches on a 2-byte boundary as this should avoid ever having to
185  // do unaligned loads if the compiler (or asm) optimises the double byte
186  // load into a single instruction
187  if(((uintptr_t)c->bytestream & 1) == 0) {
188  c->low += (1 << 9);
189  }
190  else {
191  c->low += ((*c->bytestream++) << 2) + 2;
192  }
193 #else
194  c->low = (*c->bytestream++)<<10;
195  c->low+= ((*c->bytestream++)<<2) + 2;
196 #endif
197  c->range= 0x1FE;
198  if ((c->range<<(CABAC_BITS+1)) < c->low)
199  return AVERROR_INVALIDDATA;
200  return 0;
201 }
cabac.h
init_put_bits
static void init_put_bits(PutBitContext *s, uint8_t *buffer, int buffer_size)
Initialize the PutBitContext s.
Definition: put_bits.h:48
ff_init_cabac_encoder
void ff_init_cabac_encoder(CABACContext *c, uint8_t *buf, int buf_size)
Definition: cabac.c:163
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:176
common.h
uint8_t
uint8_t
Definition: audio_convert.c:194
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:40
CABACContext
Definition: cabac.h:43
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