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 Libav.
6  *
7  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
27 #ifndef AVCODEC_RANGECODER_H
28 #define AVCODEC_RANGECODER_H
29 
30 #include <stdint.h>
31 #include <assert.h>
32 #include "libavutil/common.h"
33 
34 typedef struct RangeCoder{
35  int low;
36  int range;
39  uint8_t zero_state[256];
40  uint8_t one_state[256];
41  uint8_t *bytestream_start;
42  uint8_t *bytestream;
43  uint8_t *bytestream_end;
44 }RangeCoder;
45 
46 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
47 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
49 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
50 
51 static inline void renorm_encoder(RangeCoder *c){
52  //FIXME optimize
53  while(c->range < 0x100){
54  if(c->outstanding_byte < 0){
55  c->outstanding_byte= c->low>>8;
56  }else if(c->low <= 0xFF00){
57  *c->bytestream++ = c->outstanding_byte;
59  *c->bytestream++ = 0xFF;
60  c->outstanding_byte= c->low>>8;
61  }else if(c->low >= 0x10000){
62  *c->bytestream++ = c->outstanding_byte + 1;
64  *c->bytestream++ = 0x00;
65  c->outstanding_byte= (c->low>>8) & 0xFF;
66  }else{
67  c->outstanding_count++;
68  }
69 
70  c->low = (c->low & 0xFF)<<8;
71  c->range <<= 8;
72  }
73 }
74 
75 static inline int get_rac_count(RangeCoder *c){
76  int x= c->bytestream - c->bytestream_start + c->outstanding_count;
77  if(c->outstanding_byte >= 0)
78  x++;
79  return 8*x - av_log2(c->range);
80 }
81 
82 static inline void put_rac(RangeCoder *c, uint8_t * const state, int bit){
83  int range1= (c->range * (*state)) >> 8;
84 
85  assert(*state);
86  assert(range1 < c->range);
87  assert(range1 > 0);
88  if(!bit){
89  c->range -= range1;
90  *state= c->zero_state[*state];
91  }else{
92  c->low += c->range - range1;
93  c->range = range1;
94  *state= c->one_state[*state];
95  }
96 
97  renorm_encoder(c);
98 }
99 
100 static inline void refill(RangeCoder *c){
101  if(c->range < 0x100){
102  c->range <<= 8;
103  c->low <<= 8;
104  if(c->bytestream < c->bytestream_end)
105  c->low+= c->bytestream[0];
106  c->bytestream++;
107  }
108 }
109 
110 static inline int get_rac(RangeCoder *c, uint8_t * const state){
111  int range1= (c->range * (*state)) >> 8;
112  int av_unused one_mask;
113 
114  c->range -= range1;
115 #if 1
116  if(c->low < c->range){
117  *state= c->zero_state[*state];
118  refill(c);
119  return 0;
120  }else{
121  c->low -= c->range;
122  *state= c->one_state[*state];
123  c->range = range1;
124  refill(c);
125  return 1;
126  }
127 #else
128  one_mask= (c->range - c->low-1)>>31;
129 
130  c->low -= c->range & one_mask;
131  c->range += (range1 - c->range) & one_mask;
132 
133  *state= c->zero_state[(*state) + (256&one_mask)];
134 
135  refill(c);
136 
137  return one_mask&1;
138 #endif
139 }
140 
141 #endif /* AVCODEC_RANGECODER_H */