FFmpeg
rangecoder.h
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1 /*
2  * Range coder
3  * Copyright (c) 2004 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  * Range coder.
25  */
26 
27 #ifndef AVCODEC_RANGECODER_H
28 #define AVCODEC_RANGECODER_H
29 
30 #include <stdint.h>
31 
32 #include "libavutil/common.h"
33 #include "libavutil/avassert.h"
34 
35 typedef struct RangeCoder {
36  int low;
37  int range;
45  int overread;
46 #define MAX_OVERREAD 2
47 } RangeCoder;
48 
49 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
50 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
51 
52 /**
53  * Terminates the range coder
54  * @param version version 0 requires the decoder to know the data size in bytes
55  * version 1 needs about 1 bit more space but does not need to
56  * carry the size from encoder to decoder
57  */
59 
60 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
61 
62 static inline void renorm_encoder(RangeCoder *c)
63 {
64  // FIXME: optimize
65  while (c->range < 0x100) {
66  if (c->outstanding_byte < 0) {
67  c->outstanding_byte = c->low >> 8;
68  } else if (c->low <= 0xFF00) {
69  *c->bytestream++ = c->outstanding_byte;
70  for (; c->outstanding_count; c->outstanding_count--)
71  *c->bytestream++ = 0xFF;
72  c->outstanding_byte = c->low >> 8;
73  } else if (c->low >= 0x10000) {
74  *c->bytestream++ = c->outstanding_byte + 1;
75  for (; c->outstanding_count; c->outstanding_count--)
76  *c->bytestream++ = 0x00;
77  c->outstanding_byte = (c->low >> 8) & 0xFF;
78  } else {
79  c->outstanding_count++;
80  }
81 
82  c->low = (c->low & 0xFF) << 8;
83  c->range <<= 8;
84  }
85 }
86 
87 static inline int get_rac_count(RangeCoder *c)
88 {
89  int x = c->bytestream - c->bytestream_start + c->outstanding_count;
90  if (c->outstanding_byte >= 0)
91  x++;
92  return 8 * x - av_log2(c->range);
93 }
94 
95 static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
96 {
97  int range1 = (c->range * (*state)) >> 8;
98 
99  av_assert2(*state);
100  av_assert2(range1 < c->range);
101  av_assert2(range1 > 0);
102  if (!bit) {
103  c->range -= range1;
104  *state = c->zero_state[*state];
105  } else {
106  c->low += c->range - range1;
107  c->range = range1;
108  *state = c->one_state[*state];
109  }
110 
111  renorm_encoder(c);
112 }
113 
114 static inline void refill(RangeCoder *c)
115 {
116  if (c->range < 0x100) {
117  c->range <<= 8;
118  c->low <<= 8;
119  if (c->bytestream < c->bytestream_end) {
120  c->low += c->bytestream[0];
121  c->bytestream++;
122  } else
123  c->overread ++;
124  }
125 }
126 
127 static inline int get_rac(RangeCoder *c, uint8_t *const state)
128 {
129  int range1 = (c->range * (*state)) >> 8;
130 
131  c->range -= range1;
132  if (c->low < c->range) {
133  *state = c->zero_state[*state];
134  refill(c);
135  return 0;
136  } else {
137  c->low -= c->range;
138  *state = c->one_state[*state];
139  c->range = range1;
140  refill(c);
141  return 1;
142  }
143 }
144 
145 #endif /* AVCODEC_RANGECODER_H */
version
Definition: libkvazaar.c:320
uint32_t low
Definition: mss3.c:64
uint8_t zero_state[256]
Definition: rangecoder.h:40
uint8_t * bytestream_end
Definition: rangecoder.h:44
int av_log2(unsigned v)
Definition: intmath.c:26
uint32_t range
Definition: mss3.c:64
uint8_t one_state[256]
Definition: rangecoder.h:41
int ff_rac_terminate(RangeCoder *c, int version)
Terminates the range coder.
Definition: rangecoder.c:109
uint8_t
static int get_rac(RangeCoder *c, uint8_t *const state)
Definition: rangecoder.h:127
#define av_assert2(cond)
assert() equivalent, that does lie in speed critical code.
Definition: avassert.h:64
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
void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
Definition: rangecoder.c:42
void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
Definition: rangecoder.c:68
static struct @321 state
static void put_rac(RangeCoder *c, uint8_t *const state, int bit)
Definition: rangecoder.h:95
static void renorm_encoder(RangeCoder *c)
Definition: rangecoder.h:62
simple assert() macros that are a bit more flexible than ISO C assert().
uint8_t * bytestream
Definition: rangecoder.h:43
static void refill(RangeCoder *c)
Definition: rangecoder.h:114
void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
Definition: rangecoder.c:53
int outstanding_byte
Definition: rangecoder.h:39
static int get_rac_count(RangeCoder *c)
Definition: rangecoder.h:87
static const int factor[16]
Definition: vf_pp7.c:77
common internal and external API header
#define bit(string, value)
Definition: cbs_mpeg2.c:58
int overread
Definition: rangecoder.h:45
int outstanding_count
Definition: rangecoder.h:38
uint8_t * bytestream_start
Definition: rangecoder.h:42