Statistics
| Branch: | Revision:

ffmpeg / libavcodec / rangecoder.c @ 2912e87a

History | View | Annotate | Download (3.85 KB)

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

    
22
/**
23
 * @file
24
 * Range coder.
25
 * based upon
26
 *    "Range encoding: an algorithm for removing redundancy from a digitised
27
 *                     message.
28
 *     G. N. N. Martin                  Presented in March 1979 to the Video &
29
 *                                      Data Recording Conference,
30
 *     IBM UK Scientific Center         held in Southampton July 24-27 1979."
31
 *
32
 */
33

    
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){
42
    c->bytestream_start=
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

    
95
/**
96
 *
97
 * @return the number of bytes written
98
 */
99
int ff_rac_terminate(RangeCoder *c){
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++){
137
START_TIMER
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++){
149
START_TIMER
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 */