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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 4349 | Serge | 1 | /* |
| 2 | * Lagarith range decoder |
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| 3 | * Copyright (c) 2009 Nathan Caldwell |
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| 4 | * Copyright (c) 2009 David Conrad |
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| 5 | * |
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| 6 | * This file is part of FFmpeg. |
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| 7 | * |
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| 8 | * FFmpeg is free software; you can redistribute it and/or |
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| 9 | * modify it under the terms of the GNU Lesser General Public |
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| 10 | * License as published by the Free Software Foundation; either |
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| 11 | * version 2.1 of the License, or (at your option) any later version. |
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| 12 | * |
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| 13 | * FFmpeg is distributed in the hope that it will be useful, |
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| 14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 16 | * Lesser General Public License for more details. |
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| 17 | * |
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| 18 | * You should have received a copy of the GNU Lesser General Public |
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| 19 | * License along with FFmpeg; if not, write to the Free Software |
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| 20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
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| 21 | */ |
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| 22 | |||
| 23 | /** |
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| 24 | * @file |
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| 25 | * Lagarith range decoder |
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| 26 | * @author Nathan Caldwell |
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| 27 | * @author David Conrad |
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| 28 | */ |
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| 29 | |||
| 30 | #include "get_bits.h" |
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| 31 | #include "lagarithrac.h" |
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| 32 | |||
| 33 | void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length) |
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| 34 | { |
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| 35 | int i, j, left; |
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| 36 | |||
| 37 | /* According to reference decoder "1st byte is garbage", |
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| 38 | * however, it gets skipped by the call to align_get_bits() |
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| 39 | */ |
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| 40 | align_get_bits(gb); |
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| 41 | left = get_bits_left(gb) >> 3; |
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| 42 | l->bytestream_start = |
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| 43 | l->bytestream = gb->buffer + get_bits_count(gb) / 8; |
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| 44 | l->bytestream_end = l->bytestream_start + left; |
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| 45 | |||
| 46 | l->range = 0x80; |
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| 47 | l->low = *l->bytestream >> 1; |
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| 48 | l->hash_shift = FFMAX((int)l->scale - 8, 0); |
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| 49 | |||
| 50 | for (i = j = 0; i < 256; i++) { |
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| 51 | unsigned r = i << l->hash_shift; |
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| 52 | while (l->prob[j + 1] <= r) |
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| 53 | j++; |
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| 54 | l->range_hash[i] = j; |
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| 55 | } |
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| 56 | |||
| 57 | /* Add conversion factor to hash_shift so we don't have to in lag_get_rac. */ |
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| 58 | l->hash_shift += 23; |
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| 59 | } |