lagarith: Convert to the new bitstream reader
[libav.git] / libavcodec / lagarithrac.c
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
25 * Lagarith range decoder
26 * @author Nathan Caldwell
27 * @author David Conrad
28 */
29
30 #include "bitstream.h"
31 #include "lagarithrac.h"
32
33 void ff_lag_rac_init(lag_rac *l, BitstreamContext *bc, 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 bitstream_align()
39 */
40 bitstream_align(bc);
41 left = bitstream_bits_left(bc) >> 3;
42 l->bytestream_start =
43 l->bytestream = bc->buffer + bitstream_tell(bc) / 8;
44 l->bytestream_end = l->bytestream_start + FFMIN(length, left);
45
46 l->range = 0x80;
47 l->low = *l->bytestream >> 1;
48 l->hash_shift = FFMAX(l->scale, 8) - 8;
49
50 for (i = j = 0; i < 256; 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 /* Add conversion factor to hash_shift so we don't have to in lag_get_rac. */
58 l->hash_shift += 23;
59 }