FFmpeg coverage


Directory: ../../../ffmpeg/
File: src/libavcodec/lagarithrac.h
Date: 2022-07-04 00:18:54
Exec Total Coverage
Lines: 24 26 92.3%
Branches: 10 12 83.3%

Line Branch Exec Source
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