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;
40  uint8_t zero_state[256];
41  uint8_t one_state[256];
42  uint8_t *bytestream_start;
43  uint8_t *bytestream;
44  uint8_t *bytestream_end;
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 */
RangeCoder::bytestream_end
uint8_t * bytestream_end
Definition: rangecoder.h:44
bit
#define bit(string, value)
Definition: cbs_mpeg2.c:58
state
static struct @319 state
refill
static void refill(RangeCoder *c)
Definition: rangecoder.h:114
avassert.h
RangeCoder::one_state
uint8_t one_state[256]
Definition: rangecoder.h:41
ff_build_rac_states
void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
Definition: rangecoder.c:68
RangeCoder::range
int range
Definition: rangecoder.h:37
RangeCoder::low
int low
Definition: rangecoder.h:36
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
RangeCoder::bytestream
uint8_t * bytestream
Definition: rangecoder.h:43
version
version
Definition: libkvazaar.c:307
RangeCoder::outstanding_count
int outstanding_count
Definition: rangecoder.h:38
av_assert2
#define av_assert2(cond)
assert() equivalent, that does lie in speed critical code.
Definition: avassert.h:64
ff_init_range_decoder
void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
Definition: rangecoder.c:53
renorm_encoder
static void renorm_encoder(RangeCoder *c)
Definition: rangecoder.h:62
common.h
get_rac
static int get_rac(RangeCoder *c, uint8_t *const state)
Definition: rangecoder.h:127
RangeCoder::overread
int overread
Definition: rangecoder.h:45
RangeCoder::outstanding_byte
int outstanding_byte
Definition: rangecoder.h:39
RangeCoder::bytestream_start
uint8_t * bytestream_start
Definition: rangecoder.h:42
ff_init_range_encoder
void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
Definition: rangecoder.c:42
get_rac_count
static int get_rac_count(RangeCoder *c)
Definition: rangecoder.h:87
factor
static const int factor[16]
Definition: vf_pp7.c:76
ff_rac_terminate
int ff_rac_terminate(RangeCoder *c, int version)
Terminates the range coder.
Definition: rangecoder.c:109
put_rac
static void put_rac(RangeCoder *c, uint8_t *const state, int bit)
Definition: rangecoder.h:95
RangeCoder
Definition: mss3.c:61
RangeCoder::zero_state
uint8_t zero_state[256]
Definition: rangecoder.h:40
av_log2
int av_log2(unsigned v)
Definition: intmath.c:26