blob: dfdfea0db38e43928281ea707279139d3ef43324
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/common.h" |
35 | #include "libavutil/intreadwrite.h" |
36 | #include "avcodec.h" |
37 | #include "get_bits.h" |
38 | |
39 | typedef struct lag_rac { |
40 | AVCodecContext *avctx; |
41 | unsigned low; |
42 | unsigned range; |
43 | unsigned scale; /**< Number of bits of precision in range. */ |
44 | unsigned hash_shift; /**< Number of bits to shift to calculate hash for radix search. */ |
45 | |
46 | const uint8_t *bytestream_start; /**< Start of input bytestream. */ |
47 | const uint8_t *bytestream; /**< Current position in input bytestream. */ |
48 | const uint8_t *bytestream_end; /**< End position of input bytestream. */ |
49 | |
50 | uint32_t prob[258]; /**< Table of cumulative probability for each symbol. */ |
51 | uint8_t range_hash[1024]; /**< Hash table mapping upper byte to approximate symbol. */ |
52 | } lag_rac; |
53 | |
54 | void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length); |
55 | |
56 | /* TODO: Optimize */ |
57 | static inline void lag_rac_refill(lag_rac *l) |
58 | { |
59 | while (l->range <= 0x800000) { |
60 | l->low <<= 8; |
61 | l->range <<= 8; |
62 | l->low |= 0xff & (AV_RB16(l->bytestream) >> 1); |
63 | if (l->bytestream < l->bytestream_end) |
64 | l->bytestream++; |
65 | } |
66 | } |
67 | |
68 | /** |
69 | * Decode a single byte from the compressed plane described by *l. |
70 | * @param l pointer to lag_rac for the current plane |
71 | * @return next byte of decoded data |
72 | */ |
73 | static inline uint8_t lag_get_rac(lag_rac *l) |
74 | { |
75 | unsigned range_scaled, low_scaled; |
76 | int val; |
77 | |
78 | lag_rac_refill(l); |
79 | |
80 | range_scaled = l->range >> l->scale; |
81 | |
82 | if (l->low < range_scaled * l->prob[255]) { |
83 | /* val = 0 is frequent enough to deserve a shortcut */ |
84 | if (l->low < range_scaled * l->prob[1]) { |
85 | val = 0; |
86 | } else { |
87 | low_scaled = l->low / (range_scaled<<(l->hash_shift)); |
88 | |
89 | val = l->range_hash[low_scaled]; |
90 | while (l->low >= range_scaled * l->prob[val + 1]) |
91 | val++; |
92 | } |
93 | |
94 | l->range = range_scaled * (l->prob[val + 1] - l->prob[val]); |
95 | } else { |
96 | val = 255; |
97 | l->range -= range_scaled * l->prob[255]; |
98 | } |
99 | |
100 | if (!l->range) |
101 | l->range = 0x80; |
102 | |
103 | l->low -= range_scaled * l->prob[val]; |
104 | |
105 | return val; |
106 | } |
107 | |
108 | |
109 | #endif /* AVCODEC_LAGARITHRAC_H */ |
110 |