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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((int)l->scale - 10, 0); | |
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 | } |