blob: 3d36d1b9e99e8d3848d2e7f33dd0f4fad0102657
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 FFmpeg. |
7 | * |
8 | * FFmpeg 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 | * FFmpeg 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 FFmpeg; 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 |
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 ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length) |
34 | { |
35 | int i, j, left; |
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 | left = get_bits_left(gb) >> 3; |
42 | l->bytestream_start = |
43 | l->bytestream = gb->buffer + get_bits_count(gb) / 8; |
44 | l->bytestream_end = l->bytestream_start + left; |
45 | |
46 | l->range = 0x80; |
47 | l->low = *l->bytestream >> 1; |
48 | l->hash_shift = FFMAX(l->scale, 10) - 10; |
49 | |
50 | for (i = j = 0; i < 1024; i++) { |
51 | unsigned r = i << l->hash_shift; |
52 | while (l->prob[j + 1] <= r) |
53 | j++; |
54 | l->range_hash[i] = j; |
55 | } |
56 | } |
57 |