rangecoder.c
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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 
34 #include <string.h>
35 
36 #include "avcodec.h"
37 #include "rangecoder.h"
38 #include "bytestream.h"
39 
40 
41 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size){
43  c->bytestream= buf;
44  c->bytestream_end= buf + buf_size;
45 
46  c->low= 0;
47  c->range= 0xFF00;
48  c->outstanding_count= 0;
49  c->outstanding_byte= -1;
50 }
51 
52 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size){
53  /* cast to avoid compiler warning */
54  ff_init_range_encoder(c, (uint8_t *) buf, buf_size);
55 
56  c->low = bytestream_get_be16(&c->bytestream);
57 }
58 
59 void ff_build_rac_states(RangeCoder *c, int factor, int max_p){
60  const int64_t one= 1LL<<32;
61  int64_t p;
62  int last_p8, p8, i;
63 
64  memset(c->zero_state, 0, sizeof(c->zero_state));
65  memset(c-> one_state, 0, sizeof(c-> one_state));
66 
67  last_p8= 0;
68  p= one/2;
69  for(i=0; i<128; i++){
70  p8= (256*p + one/2) >> 32; //FIXME try without the one
71  if(p8 <= last_p8) p8= last_p8+1;
72  if(last_p8 && last_p8<256 && p8<=max_p)
73  c->one_state[last_p8]= p8;
74 
75  p+= ((one-p)*factor + one/2) >> 32;
76  last_p8= p8;
77  }
78 
79  for(i=256-max_p; i<=max_p; i++){
80  if(c->one_state[i])
81  continue;
82 
83  p= (i*one + 128) >> 8;
84  p+= ((one-p)*factor + one/2) >> 32;
85  p8= (256*p + one/2) >> 32; //FIXME try without the one
86  if(p8 <= i) p8= i+1;
87  if(p8 > max_p) p8= max_p;
88  c->one_state[ i]= p8;
89  }
90 
91  for(i=1; i<255; i++)
92  c->zero_state[i]= 256-c->one_state[256-i];
93 }
94 
100  c->range=0xFF;
101  c->low +=0xFF;
102  renorm_encoder(c);
103  c->range=0xFF;
104  renorm_encoder(c);
105 
106  assert(c->low == 0);
107  assert(c->range >= 0x100);
108 
109  return c->bytestream - c->bytestream_start;
110 }
111 
112 #ifdef TEST
113 #define SIZE 10240
114 
115 #include "libavutil/lfg.h"
116 
117 int main(void){
118  RangeCoder c;
119  uint8_t b[9*SIZE];
120  uint8_t r[9*SIZE];
121  int i;
122  uint8_t state[10]= {0};
123  AVLFG prng;
124 
125  av_lfg_init(&prng, 1);
126 
127  ff_init_range_encoder(&c, b, SIZE);
128  ff_build_rac_states(&c, 0.05*(1LL<<32), 128+64+32+16);
129 
130  memset(state, 128, sizeof(state));
131 
132  for(i=0; i<SIZE; i++){
133  r[i] = av_lfg_get(&prng) % 7;
134  }
135 
136  for(i=0; i<SIZE; i++){
138  put_rac(&c, state, r[i]&1);
139 STOP_TIMER("put_rac")
140  }
141 
142  ff_rac_terminate(&c);
143 
144  ff_init_range_decoder(&c, b, SIZE);
145 
146  memset(state, 128, sizeof(state));
147 
148  for(i=0; i<SIZE; i++){
150  if( (r[i]&1) != get_rac(&c, state) )
151  av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i);
152 STOP_TIMER("get_rac")
153  }
154 
155  return 0;
156 }
157 #endif /* TEST */