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
|
/*
* Lagarith range decoder
* Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com>
* Copyright (c) 2009 David Conrad
*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* Lagarith range decoder
* @author Nathan Caldwell
* @author David Conrad
*/
#include "bitstream.h"
#include "lagarithrac.h"
void ff_lag_rac_init(lag_rac *l, BitstreamContext *bc, int length)
{
int i, j, left;
/* According to reference decoder "1st byte is garbage",
* however, it gets skipped by the call to bitstream_align()
*/
bitstream_align(bc);
left = bitstream_bits_left(bc) >> 3;
l->bytestream_start =
l->bytestream = bc->buffer + bitstream_tell(bc) / 8;
l->bytestream_end = l->bytestream_start + FFMIN(length, left);
l->range = 0x80;
l->low = *l->bytestream >> 1;
l->hash_shift = FFMAX(l->scale, 8) - 8;
for (i = j = 0; i < 256; i++) {
unsigned r = i << l->hash_shift;
while (l->prob[j + 1] <= r)
j++;
l->range_hash[i] = j;
}
/* Add conversion factor to hash_shift so we don't have to in lag_get_rac. */
l->hash_shift += 23;
}
|
