yading@10: /*
yading@10:  * Lagarith range decoder
yading@10:  * Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com>
yading@10:  * Copyright (c) 2009 David Conrad
yading@10:  *
yading@10:  * This file is part of FFmpeg.
yading@10:  *
yading@10:  * FFmpeg is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * FFmpeg is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with FFmpeg; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * @file
yading@10:  * Lagarith range decoder
yading@10:  * @author Nathan Caldwell
yading@10:  * @author David Conrad
yading@10:  */
yading@10: 
yading@10: #include "get_bits.h"
yading@10: #include "lagarithrac.h"
yading@10: 
yading@10: void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length)
yading@10: {
yading@10:     int i, j, left;
yading@10: 
yading@10:     /* According to reference decoder "1st byte is garbage",
yading@10:      * however, it gets skipped by the call to align_get_bits()
yading@10:      */
yading@10:     align_get_bits(gb);
yading@10:     left                = get_bits_left(gb) >> 3;
yading@10:     l->bytestream_start =
yading@10:     l->bytestream       = gb->buffer + get_bits_count(gb) / 8;
yading@10:     l->bytestream_end   = l->bytestream_start + left;
yading@10: 
yading@10:     l->range        = 0x80;
yading@10:     l->low          = *l->bytestream >> 1;
yading@10:     l->hash_shift   = FFMAX((int)l->scale - 8, 0);
yading@10: 
yading@10:     for (i = j = 0; i < 256; i++) {
yading@10:         unsigned r = i << l->hash_shift;
yading@10:         while (l->prob[j + 1] <= r)
yading@10:             j++;
yading@10:         l->range_hash[i] = j;
yading@10:     }
yading@10: 
yading@10:     /* Add conversion factor to hash_shift so we don't have to in lag_get_rac. */
yading@10:     l->hash_shift += 23;
yading@10: }