| 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 | } |