mirror of https://git.ffmpeg.org/ffmpeg.git
59 lines
1.8 KiB
C
59 lines
1.8 KiB
C
/*
|
|
* Lagarith range decoder
|
|
* Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com>
|
|
* Copyright (c) 2009 David Conrad
|
|
*
|
|
* This file is part of Libav.
|
|
*
|
|
* Libav 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.
|
|
*
|
|
* Libav 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 Libav; 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 lag_rac_init(lag_rac *l, GetBitContext *gb, int length)
|
|
{
|
|
int i, j;
|
|
|
|
/* According to reference decoder "1st byte is garbage",
|
|
* however, it gets skipped by the call to align_get_bits()
|
|
*/
|
|
align_get_bits(gb);
|
|
l->bytestream_start =
|
|
l->bytestream = gb->buffer + get_bits_count(gb) / 8;
|
|
l->bytestream_end = l->bytestream_start + length;
|
|
|
|
l->range = 0x80;
|
|
l->low = *l->bytestream >> 1;
|
|
l->hash_shift = FFMAX(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;
|
|
}
|