0,0 → 1,59 |
/* |
* Lagarith range decoder |
* Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com> |
* Copyright (c) 2009 David Conrad |
* |
* This file is part of FFmpeg. |
* |
* FFmpeg is free software; you can redistribute it and/or |
* modify it under the terms of the GNU Lesser General Public |
* License as published by the Free Software Foundation; either |
* version 2.1 of the License, or (at your option) any later version. |
* |
* FFmpeg is distributed in the hope that it will be useful, |
* but WITHOUT ANY WARRANTY; without even the implied warranty of |
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
* Lesser General Public License for more details. |
* |
* You should have received a copy of the GNU Lesser General Public |
* License along with FFmpeg; if not, write to the Free Software |
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
*/ |
|
/** |
* @file |
* Lagarith range decoder |
* @author Nathan Caldwell |
* @author David Conrad |
*/ |
|
#include "get_bits.h" |
#include "lagarithrac.h" |
|
void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length) |
{ |
int i, j, left; |
|
/* According to reference decoder "1st byte is garbage", |
* however, it gets skipped by the call to align_get_bits() |
*/ |
align_get_bits(gb); |
left = get_bits_left(gb) >> 3; |
l->bytestream_start = |
l->bytestream = gb->buffer + get_bits_count(gb) / 8; |
l->bytestream_end = l->bytestream_start + left; |
|
l->range = 0x80; |
l->low = *l->bytestream >> 1; |
l->hash_shift = FFMAX((int)l->scale - 8, 0); |
|
for (i = j = 0; i < 256; i++) { |
unsigned r = i << l->hash_shift; |
while (l->prob[j + 1] <= r) |
j++; |
l->range_hash[i] = j; |
} |
|
/* Add conversion factor to hash_shift so we don't have to in lag_get_rac. */ |
l->hash_shift += 23; |
} |