/* * 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; }