Statistics
| Branch: | Revision:

ffmpeg / libavcodec / lagarithrac.c @ 2912e87a

History | View | Annotate | Download (1.79 KB)

1
/*
2
 * Lagarith range decoder
3
 * Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com>
4
 * Copyright (c) 2009 David Conrad
5
 *
6
 * This file is part of Libav.
7
 *
8
 * Libav is free software; you can redistribute it and/or
9
 * modify it under the terms of the GNU Lesser General Public
10
 * License as published by the Free Software Foundation; either
11
 * version 2.1 of the License, or (at your option) any later version.
12
 *
13
 * Libav is distributed in the hope that it will be useful,
14
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
16
 * Lesser General Public License for more details.
17
 *
18
 * You should have received a copy of the GNU Lesser General Public
19
 * License along with Libav; if not, write to the Free Software
20
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21
 */
22

    
23
/**
24
 * @file libavcodec/lagarithrac.c
25
 * Lagarith range decoder
26
 * @author Nathan Caldwell
27
 * @author David Conrad
28
 */
29

    
30
#include "get_bits.h"
31
#include "lagarithrac.h"
32

    
33
void lag_rac_init(lag_rac *l, GetBitContext *gb, int length)
34
{
35
    int i, j;
36

    
37
    /* According to reference decoder "1st byte is garbage",
38
     * however, it gets skipped by the call to align_get_bits()
39
     */
40
    align_get_bits(gb);
41
    l->bytestream_start =
42
    l->bytestream       = gb->buffer + get_bits_count(gb) / 8;
43
    l->bytestream_end   = l->bytestream_start + length;
44

    
45
    l->range        = 0x80;
46
    l->low          = *l->bytestream >> 1;
47
    l->hash_shift   = FFMAX(l->scale - 8, 0);
48

    
49
    for (i = j = 0; i < 256; i++) {
50
        unsigned r = i << l->hash_shift;
51
        while (l->prob[j + 1] <= r)
52
            j++;
53
        l->range_hash[i] = j;
54
    }
55

    
56
    /* Add conversion factor to hash_shift so we don't have to in lag_get_rac. */
57
    l->hash_shift += 23;
58
}