FFmpeg coverage

Directory: ../../../ffmpeg/
File: src/libavcodec/lagarithrac.h
Date: 2024-11-20 23:03:26
Exec Total Coverage
Lines: 24 26 92.3%
Functions: 2 2 100.0%
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 "get_bits.h"
36
37 typedef struct lag_rac {
38 void *logctx;
39 unsigned low;
40 unsigned range;
41 unsigned scale; /**< Number of bits of precision in range. */
42 unsigned hash_shift; /**< Number of bits to shift to calculate hash for radix search. */
43
44 const uint8_t *bytestream_start; /**< Start of input bytestream. */
45 const uint8_t *bytestream; /**< Current position in input bytestream. */
46 const uint8_t *bytestream_end; /**< End position of input bytestream. */
47
48 int overread;
49 #define MAX_OVERREAD 4
50
51 uint32_t prob[258]; /**< Table of cumulative probability for each symbol. */
52 uint8_t range_hash[1024]; /**< Hash table mapping upper byte to approximate symbol. */
53 } lag_rac;
54
55 void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length);
56
57 /* TODO: Optimize */
58 4610091 static inline void lag_rac_refill(lag_rac *l)
59 {
60
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 6421816 while (l->range <= 0x800000) {
61 1811725 l->low <<= 8;
62 1811725 l->range <<= 8;
63 1811725 l->low |= 0xff & (AV_RB16(l->bytestream) >> 1);
64
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 1811725 if (l->bytestream < l->bytestream_end)
65 1811725 l->bytestream++;
66 else
67 ✗ l->overread++;
68 }
69 4610091 }
70
71 /**
72 * Decode a single byte from the compressed plane described by *l.
73 * @param l pointer to lag_rac for the current plane
74 * @return next byte of decoded data
75 */
76 4610091 static inline uint8_t lag_get_rac(lag_rac *l)
77 {
78 unsigned range_scaled, low_scaled;
79 int val;
80
81 4610091 lag_rac_refill(l);
82
83 4610091 range_scaled = l->range >> l->scale;
84
85
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 4610091 if (l->low < range_scaled * l->prob[255]) {
86 /* val = 0 is frequent enough to deserve a shortcut */
87
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 3832002 if (l->low < range_scaled * l->prob[1]) {
88 1476885 val = 0;
89 } else {
90 2355117 low_scaled = l->low / (range_scaled<<(l->hash_shift));
91
92 2355117 val = l->range_hash[low_scaled];
93
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 2875612 while (l->low >= range_scaled * l->prob[val + 1])
94 520495 val++;
95 }
96
97 3832002 l->range = range_scaled * (l->prob[val + 1] - l->prob[val]);
98 } else {
99 778089 val = 255;
100 778089 l->range -= range_scaled * l->prob[255];
101 }
102
103
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 4610091 if (!l->range)
104 ✗ l->range = 0x80;
105
106 4610091 l->low -= range_scaled * l->prob[val];
107
108 4610091 return val;
109 }
110
111
112 #endif /* AVCODEC_LAGARITHRAC_H */
113