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1 | /* | ||
2 | * Lagarith range decoder | ||
3 | * Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com> | ||
4 | * Copyright (c) 2009 David Conrad | ||
5 | * | ||
6 | * This file is part of FFmpeg. | ||
7 | * | ||
8 | * FFmpeg is free software; you can redistribute it and/or | ||
9 | * modify it under the terms of the GNU Lesser General Public | ||
10 | * License as published by the Free Software Foundation; either | ||
11 | * version 2.1 of the License, or (at your option) any later version. | ||
12 | * | ||
13 | * FFmpeg is distributed in the hope that it will be useful, | ||
14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
16 | * Lesser General Public License for more details. | ||
17 | * | ||
18 | * You should have received a copy of the GNU Lesser General Public | ||
19 | * License along with FFmpeg; if not, write to the Free Software | ||
20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | ||
21 | */ | ||
22 | |||
23 | /** | ||
24 | * @file | ||
25 | * Lagarith range decoder | ||
26 | * @author Nathan Caldwell | ||
27 | * @author David Conrad | ||
28 | */ | ||
29 | |||
30 | #ifndef AVCODEC_LAGARITHRAC_H | ||
31 | #define AVCODEC_LAGARITHRAC_H | ||
32 | |||
33 | #include <stdint.h> | ||
34 | #include "libavutil/intreadwrite.h" | ||
35 | #include "avcodec.h" | ||
36 | #include "get_bits.h" | ||
37 | |||
38 | typedef struct lag_rac { | ||
39 | AVCodecContext *avctx; | ||
40 | unsigned low; | ||
41 | unsigned range; | ||
42 | unsigned scale; /**< Number of bits of precision in range. */ | ||
43 | unsigned hash_shift; /**< Number of bits to shift to calculate hash for radix search. */ | ||
44 | |||
45 | const uint8_t *bytestream_start; /**< Start of input bytestream. */ | ||
46 | const uint8_t *bytestream; /**< Current position in input bytestream. */ | ||
47 | const uint8_t *bytestream_end; /**< End position of input bytestream. */ | ||
48 | |||
49 | int overread; | ||
50 | #define MAX_OVERREAD 4 | ||
51 | |||
52 | uint32_t prob[258]; /**< Table of cumulative probability for each symbol. */ | ||
53 | uint8_t range_hash[1024]; /**< Hash table mapping upper byte to approximate symbol. */ | ||
54 | } lag_rac; | ||
55 | |||
56 | void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length); | ||
57 | |||
58 | /* TODO: Optimize */ | ||
59 | 4610091 | static inline void lag_rac_refill(lag_rac *l) | |
60 | { | ||
61 |
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6421816 | while (l->range <= 0x800000) { |
62 | 1811725 | l->low <<= 8; | |
63 | 1811725 | l->range <<= 8; | |
64 | 1811725 | l->low |= 0xff & (AV_RB16(l->bytestream) >> 1); | |
65 |
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1811725 | if (l->bytestream < l->bytestream_end) |
66 | 1811725 | l->bytestream++; | |
67 | else | ||
68 | ✗ | l->overread++; | |
69 | } | ||
70 | 4610091 | } | |
71 | |||
72 | /** | ||
73 | * Decode a single byte from the compressed plane described by *l. | ||
74 | * @param l pointer to lag_rac for the current plane | ||
75 | * @return next byte of decoded data | ||
76 | */ | ||
77 | 4610091 | static inline uint8_t lag_get_rac(lag_rac *l) | |
78 | { | ||
79 | unsigned range_scaled, low_scaled; | ||
80 | int val; | ||
81 | |||
82 | 4610091 | lag_rac_refill(l); | |
83 | |||
84 | 4610091 | range_scaled = l->range >> l->scale; | |
85 | |||
86 |
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4610091 | if (l->low < range_scaled * l->prob[255]) { |
87 | /* val = 0 is frequent enough to deserve a shortcut */ | ||
88 |
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3832002 | if (l->low < range_scaled * l->prob[1]) { |
89 | 1476885 | val = 0; | |
90 | } else { | ||
91 | 2355117 | low_scaled = l->low / (range_scaled<<(l->hash_shift)); | |
92 | |||
93 | 2355117 | val = l->range_hash[low_scaled]; | |
94 |
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2875612 | while (l->low >= range_scaled * l->prob[val + 1]) |
95 | 520495 | val++; | |
96 | } | ||
97 | |||
98 | 3832002 | l->range = range_scaled * (l->prob[val + 1] - l->prob[val]); | |
99 | } else { | ||
100 | 778089 | val = 255; | |
101 | 778089 | l->range -= range_scaled * l->prob[255]; | |
102 | } | ||
103 | |||
104 |
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4610091 | if (!l->range) |
105 | ✗ | l->range = 0x80; | |
106 | |||
107 | 4610091 | l->low -= range_scaled * l->prob[val]; | |
108 | |||
109 | 4610091 | return val; | |
110 | } | ||
111 | |||
112 | |||
113 | #endif /* AVCODEC_LAGARITHRAC_H */ | ||
114 |