1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
/*
* Range coder
* Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file libavcodec/rangecoder.c
* Range coder.
* based upon
* "Range encoding: an algorithm for removing redundancy from a digitised
* message.
* G. N. N. Martin Presented in March 1979 to the Video &
* Data Recording Conference,
* IBM UK Scientific Center held in Southampton July 24-27 1979."
*
*/
#include <string.h>
#include "avcodec.h"
#include "rangecoder.h"
#include "bytestream.h"
void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size){
c->bytestream_start=
c->bytestream= buf;
c->bytestream_end= buf + buf_size;
c->low= 0;
c->range= 0xFF00;
c->outstanding_count= 0;
c->outstanding_byte= -1;
}
void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size){
/* cast to avoid compiler warning */
ff_init_range_encoder(c, (uint8_t *) buf, buf_size);
c->low = bytestream_get_be16(&c->bytestream);
}
void ff_build_rac_states(RangeCoder *c, int factor, int max_p){
const int64_t one= 1LL<<32;
int64_t p;
int last_p8, p8, i;
memset(c->zero_state, 0, sizeof(c->zero_state));
memset(c-> one_state, 0, sizeof(c-> one_state));
last_p8= 0;
p= one/2;
for(i=0; i<128; i++){
p8= (256*p + one/2) >> 32; //FIXME try without the one
if(p8 <= last_p8) p8= last_p8+1;
if(last_p8 && last_p8<256 && p8<=max_p)
c->one_state[last_p8]= p8;
p+= ((one-p)*factor + one/2) >> 32;
last_p8= p8;
}
for(i=256-max_p; i<=max_p; i++){
if(c->one_state[i])
continue;
p= (i*one + 128) >> 8;
p+= ((one-p)*factor + one/2) >> 32;
p8= (256*p + one/2) >> 32; //FIXME try without the one
if(p8 <= i) p8= i+1;
if(p8 > max_p) p8= max_p;
c->one_state[ i]= p8;
}
for(i=1; i<255; i++)
c->zero_state[i]= 256-c->one_state[256-i];
}
/**
*
* @return the number of bytes written
*/
int ff_rac_terminate(RangeCoder *c){
c->range=0xFF;
c->low +=0xFF;
renorm_encoder(c);
c->range=0xFF;
renorm_encoder(c);
assert(c->low == 0);
assert(c->range >= 0x100);
return c->bytestream - c->bytestream_start;
}
#ifdef TEST
#define SIZE 10240
#include "libavutil/lfg.h"
int main(void){
RangeCoder c;
uint8_t b[9*SIZE];
uint8_t r[9*SIZE];
int i;
uint8_t state[10]= {0};
AVLFG prn;
av_lfg_init(&prn, 1);
ff_init_range_encoder(&c, b, SIZE);
ff_build_rac_states(&c, 0.05*(1LL<<32), 128+64+32+16);
memset(state, 128, sizeof(state));
for(i=0; i<SIZE; i++){
r[i] = av_lfg_get(&prn) % 7;
}
for(i=0; i<SIZE; i++){
START_TIMER
put_rac(&c, state, r[i]&1);
STOP_TIMER("put_rac")
}
ff_rac_terminate(&c);
ff_init_range_decoder(&c, b, SIZE);
memset(state, 128, sizeof(state));
for(i=0; i<SIZE; i++){
START_TIMER
if( (r[i]&1) != get_rac(&c, state) )
av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i);
STOP_TIMER("get_rac")
}
return 0;
}
#endif /* TEST */
|
