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