FFmpeg  4.3.8
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 /**
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 */
version
Definition: libkvazaar.c:292
static struct @314 state
uint32_t low
Definition: mss3.c:64
uint8_t zero_state[256]
Definition: rangecoder.h:40
uint8_t * bytestream_end
Definition: rangecoder.h:44
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
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
#define av_log2
Definition: intmath.h:83
int outstanding_byte
Definition: rangecoder.h:39
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
static double c[64]
int outstanding_count
Definition: rangecoder.h:38
uint8_t * bytestream_start
Definition: rangecoder.h:42