FFmpeg
dirac_arith.c
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1 /*
2  * Copyright (C) 2007 Marco Gerards <marco@gnu.org>
3  * Copyright (C) 2009 David Conrad
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  * Arithmetic decoder for Dirac
25  * @author Marco Gerards <marco@gnu.org>
26  */
27 
28 #include "dirac_arith.h"
29 
30 
31 const uint16_t ff_dirac_prob[256] = {
32  0, 2, 5, 8, 11, 15, 20, 24,
33  29, 35, 41, 47, 53, 60, 67, 74,
34  82, 89, 97, 106, 114, 123, 132, 141,
35  150, 160, 170, 180, 190, 201, 211, 222,
36  233, 244, 256, 267, 279, 291, 303, 315,
37  327, 340, 353, 366, 379, 392, 405, 419,
38  433, 447, 461, 475, 489, 504, 518, 533,
39  548, 563, 578, 593, 609, 624, 640, 656,
40  672, 688, 705, 721, 738, 754, 771, 788,
41  805, 822, 840, 857, 875, 892, 910, 928,
42  946, 964, 983, 1001, 1020, 1038, 1057, 1076,
43  1095, 1114, 1133, 1153, 1172, 1192, 1211, 1231,
44  1251, 1271, 1291, 1311, 1332, 1352, 1373, 1393,
45  1414, 1435, 1456, 1477, 1498, 1520, 1541, 1562,
46  1584, 1606, 1628, 1649, 1671, 1694, 1716, 1738,
47  1760, 1783, 1806, 1828, 1851, 1874, 1897, 1920,
48  1935, 1942, 1949, 1955, 1961, 1968, 1974, 1980,
49  1985, 1991, 1996, 2001, 2006, 2011, 2016, 2021,
50  2025, 2029, 2033, 2037, 2040, 2044, 2047, 2050,
51  2053, 2056, 2058, 2061, 2063, 2065, 2066, 2068,
52  2069, 2070, 2071, 2072, 2072, 2072, 2072, 2072,
53  2072, 2071, 2070, 2069, 2068, 2066, 2065, 2063,
54  2060, 2058, 2055, 2052, 2049, 2045, 2042, 2038,
55  2033, 2029, 2024, 2019, 2013, 2008, 2002, 1996,
56  1989, 1982, 1975, 1968, 1960, 1952, 1943, 1934,
57  1925, 1916, 1906, 1896, 1885, 1874, 1863, 1851,
58  1839, 1827, 1814, 1800, 1786, 1772, 1757, 1742,
59  1727, 1710, 1694, 1676, 1659, 1640, 1622, 1602,
60  1582, 1561, 1540, 1518, 1495, 1471, 1447, 1422,
61  1396, 1369, 1341, 1312, 1282, 1251, 1219, 1186,
62  1151, 1114, 1077, 1037, 995, 952, 906, 857,
63  805, 750, 690, 625, 553, 471, 376, 255
64 };
65 
69  [CTX_ZP_F2] = CTX_ZP_F3,
70  [CTX_ZP_F3] = CTX_ZP_F4,
71  [CTX_ZP_F4] = CTX_ZP_F5,
72  [CTX_ZP_F5] = CTX_ZP_F6,
73  [CTX_ZP_F6] = CTX_ZP_F6,
76  [CTX_NP_F2] = CTX_NP_F3,
77  [CTX_NP_F3] = CTX_NP_F4,
78  [CTX_NP_F4] = CTX_NP_F5,
79  [CTX_NP_F5] = CTX_NP_F6,
80  [CTX_NP_F6] = CTX_NP_F6,
82 };
83 
84 int16_t ff_dirac_prob_branchless[256][2];
85 
87 {
88  int i;
89 
90  for (i = 0; i < 256; i++) {
93  }
94 }
95 
97 {
98  int i;
99  align_get_bits(gb);
100 
101  length = FFMIN(length, get_bits_left(gb)/8);
102 
103  c->bytestream = gb->buffer + get_bits_count(gb)/8;
104  c->bytestream_end = c->bytestream + length;
105  skip_bits_long(gb, length*8);
106 
107  c->low = 0;
108  for (i = 0; i < 4; i++) {
109  c->low <<= 8;
110  if (c->bytestream < c->bytestream_end)
111  c->low |= *c->bytestream++;
112  else
113  c->low |= 0xff;
114  }
115 
116  c->counter = -16;
117  c->range = 0xffff;
118  c->error = 0;
119  c->overread= 0;
120 
121  for (i = 0; i < DIRAC_CTX_COUNT; i++)
122  c->contexts[i] = 0x8000;
123 }
int16_t ff_dirac_prob_branchless[256][2]
Definition: dirac_arith.c:84
static void skip_bits_long(GetBitContext *s, int n)
Skips the specified number of bits.
Definition: get_bits.h:291
const uint8_t ff_dirac_next_ctx[DIRAC_CTX_COUNT]
Definition: dirac_arith.c:66
void ff_dirac_init_arith_decoder(DiracArith *c, GetBitContext *gb, int length)
Definition: dirac_arith.c:96
uint16_t contexts[DIRAC_CTX_COUNT]
Definition: dirac_arith.h:83
const uint8_t * buffer
Definition: get_bits.h:62
int16_t counter
Definition: dirac_arith.h:78
uint8_t
#define av_cold
Definition: attributes.h:82
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
static int get_bits_count(const GetBitContext *s)
Definition: get_bits.h:219
uint16_t range
Definition: dirac_arith.h:77
static int get_bits_left(GetBitContext *gb)
Definition: get_bits.h:849
#define i(width, name, range_min, range_max)
Definition: cbs_h2645.c:259
GLsizei GLsizei * length
Definition: opengl_enc.c:114
#define FFMIN(a, b)
Definition: common.h:96
const uint8_t * bytestream
Definition: dirac_arith.h:80
const uint16_t ff_dirac_prob[256]
Definition: dirac_arith.c:31
const uint8_t * bytestream_end
Definition: dirac_arith.h:81
Arithmetic decoder for Dirac.
int overread
Definition: dirac_arith.h:85
unsigned low
Definition: dirac_arith.h:76
static const uint8_t * align_get_bits(GetBitContext *s)
Definition: get_bits.h:693
av_cold void ff_dirac_init_arith_tables(void)
Definition: dirac_arith.c:86