FFmpeg
rangecoder.h
Go to the documentation of this file.
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 /**
61  * Check if at the current position there is a valid looking termination
62  * @param version version 0 requires the decoder to know the data size in bytes
63  * version 1 needs about 1 bit more space but does not need to
64  * carry the size from encoder to decoder
65  * @returns negative AVERROR code on error or non negative.
66  */
68 
69 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
70 
71 static inline void renorm_encoder(RangeCoder *c)
72 {
73  // FIXME: optimize
74  while (c->range < 0x100) {
75  if (c->outstanding_byte < 0) {
76  c->outstanding_byte = c->low >> 8;
77  } else if (c->low <= 0xFF00) {
78  *c->bytestream++ = c->outstanding_byte;
79  for (; c->outstanding_count; c->outstanding_count--)
80  *c->bytestream++ = 0xFF;
81  c->outstanding_byte = c->low >> 8;
82  } else if (c->low >= 0x10000) {
83  *c->bytestream++ = c->outstanding_byte + 1;
84  for (; c->outstanding_count; c->outstanding_count--)
85  *c->bytestream++ = 0x00;
86  c->outstanding_byte = (c->low >> 8) & 0xFF;
87  } else {
88  c->outstanding_count++;
89  }
90 
91  c->low = (c->low & 0xFF) << 8;
92  c->range <<= 8;
93  }
94 }
95 
96 static inline int get_rac_count(RangeCoder *c)
97 {
98  int x = c->bytestream - c->bytestream_start + c->outstanding_count;
99  if (c->outstanding_byte >= 0)
100  x++;
101  return 8 * x - av_log2(c->range);
102 }
103 
104 static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
105 {
106  int range1 = (c->range * (*state)) >> 8;
107 
108  av_assert2(*state);
109  av_assert2(range1 < c->range);
110  av_assert2(range1 > 0);
111  if (!bit) {
112  c->range -= range1;
113  *state = c->zero_state[*state];
114  } else {
115  c->low += c->range - range1;
116  c->range = range1;
117  *state = c->one_state[*state];
118  }
119 
120  renorm_encoder(c);
121 }
122 
123 static inline void refill(RangeCoder *c)
124 {
125  if (c->range < 0x100) {
126  c->range <<= 8;
127  c->low <<= 8;
128  if (c->bytestream < c->bytestream_end) {
129  c->low += c->bytestream[0];
130  c->bytestream++;
131  } else
132  c->overread ++;
133  }
134 }
135 
136 static inline int get_rac(RangeCoder *c, uint8_t *const state)
137 {
138  int range1 = (c->range * (*state)) >> 8;
139 
140  c->range -= range1;
141  if (c->low < c->range) {
142  *state = c->zero_state[*state];
143  refill(c);
144  return 0;
145  } else {
146  c->low -= c->range;
147  *state = c->one_state[*state];
148  c->range = range1;
149  refill(c);
150  return 1;
151  }
152 }
153 
154 #endif /* AVCODEC_RANGECODER_H */
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
int version
Definition: avisynth_c.h:858
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:136
#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 void put_rac(RangeCoder *c, uint8_t *const state, int bit)
Definition: rangecoder.h:104
int ff_rac_check_termination(RangeCoder *c, int version)
Check if at the current position there is a valid looking termination.
Definition: rangecoder.c:125
static void renorm_encoder(RangeCoder *c)
Definition: rangecoder.h:71
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:123
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 struct @320 state
void * buf
Definition: avisynth_c.h:766
static int get_rac_count(RangeCoder *c)
Definition: rangecoder.h:96
static const int factor[16]
Definition: vf_pp7.c:75
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