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 "get_bits.h"
31#include "lagarithrac.h"
32
33void 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 + FFMIN(length, left);
45
46    l->range        = 0x80;
47    l->low          = *l->bytestream >> 1;
48    l->hash_shift   = FFMAX(l->scale - 8, 0);
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}
60