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/*
* 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 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;
}
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