FFmpeg  4.4.5
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 */
uint8_t
simple assert() macros that are a bit more flexible than ISO C assert().
#define av_assert2(cond)
assert() equivalent, that does lie in speed critical code.
Definition: avassert.h:64
#define bit(string, value)
Definition: cbs_mpeg2.c:58
static struct @321 state
common internal and external API header
#define av_log2
Definition: intmath.h:83
version
Definition: libkvazaar.c:326
int ff_rac_terminate(RangeCoder *c, int version)
Terminates the range coder.
Definition: rangecoder.c:109
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
void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
Definition: rangecoder.c:53
static void refill(RangeCoder *c)
Definition: rangecoder.h:114
static int get_rac_count(RangeCoder *c)
Definition: rangecoder.h:87
static int get_rac(RangeCoder *c, uint8_t *const state)
Definition: rangecoder.h:127
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
uint8_t * bytestream_start
Definition: rangecoder.h:42
uint8_t * bytestream
Definition: rangecoder.h:43
int outstanding_count
Definition: rangecoder.h:38
uint8_t * bytestream_end
Definition: rangecoder.h:44
uint8_t one_state[256]
Definition: rangecoder.h:41
int outstanding_byte
Definition: rangecoder.h:39
uint8_t zero_state[256]
Definition: rangecoder.h:40
int overread
Definition: rangecoder.h:45
static const int factor[16]
Definition: vf_pp7.c:77
static double c[64]