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lagarithrac.h
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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/common.h"
35 #include "libavutil/intreadwrite.h"
36 #include "avcodec.h"
37 #include "get_bits.h"
38 
39 typedef struct lag_rac {
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  int overread;
51 #define MAX_OVERREAD 4
52 
53  uint32_t prob[258]; /**< Table of cumulative probability for each symbol. */
54  uint8_t range_hash[1024]; /**< Hash table mapping upper byte to approximate symbol. */
55 } lag_rac;
56 
57 void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length);
58 
59 /* TODO: Optimize */
60 static inline void lag_rac_refill(lag_rac *l)
61 {
62  while (l->range <= 0x800000) {
63  l->low <<= 8;
64  l->range <<= 8;
65  l->low |= 0xff & (AV_RB16(l->bytestream) >> 1);
66  if (l->bytestream < l->bytestream_end)
67  l->bytestream++;
68  else
69  l->overread++;
70  }
71 }
72 
73 /**
74  * Decode a single byte from the compressed plane described by *l.
75  * @param l pointer to lag_rac for the current plane
76  * @return next byte of decoded data
77  */
78 static inline uint8_t lag_get_rac(lag_rac *l)
79 {
80  unsigned range_scaled, low_scaled;
81  int val;
82 
83  lag_rac_refill(l);
84 
85  range_scaled = l->range >> l->scale;
86 
87  if (l->low < range_scaled * l->prob[255]) {
88  /* val = 0 is frequent enough to deserve a shortcut */
89  if (l->low < range_scaled * l->prob[1]) {
90  val = 0;
91  } else {
92  low_scaled = l->low / (range_scaled<<(l->hash_shift));
93 
94  val = l->range_hash[low_scaled];
95  while (l->low >= range_scaled * l->prob[val + 1])
96  val++;
97  }
98 
99  l->range = range_scaled * (l->prob[val + 1] - l->prob[val]);
100  } else {
101  val = 255;
102  l->range -= range_scaled * l->prob[255];
103  }
104 
105  if (!l->range)
106  l->range = 0x80;
107 
108  l->low -= range_scaled * l->prob[val];
109 
110  return val;
111 }
112 
113 
114 #endif /* AVCODEC_LAGARITHRAC_H */
AVCodecContext * avctx
Definition: lagarithrac.h:40
static uint8_t lag_get_rac(lag_rac *l)
Decode a single byte from the compressed plane described by *l.
Definition: lagarithrac.h:78
const char const char void * val
Definition: avisynth_c.h:771
uint64_t_TMPL AV_WL64 unsigned int_TMPL AV_WL32 unsigned int_TMPL AV_WL24 unsigned int_TMPL AV_WL16 uint64_t_TMPL AV_WB64 unsigned int_TMPL AV_WB32 unsigned int_TMPL AV_WB24 unsigned int_TMPL AV_RB16
Definition: bytestream.h:87
const uint8_t * bytestream_end
End position of input bytestream.
Definition: lagarithrac.h:48
uint8_t
const uint8_t * bytestream_start
Start of input bytestream.
Definition: lagarithrac.h:46
unsigned scale
Number of bits of precision in range.
Definition: lagarithrac.h:43
bitstream reader API header.
GLsizei GLsizei * length
Definition: opengl_enc.c:115
Libavcodec external API header.
uint32_t prob[258]
Table of cumulative probability for each symbol.
Definition: lagarithrac.h:53
main external API structure.
Definition: avcodec.h:1488
int overread
Definition: lagarithrac.h:50
uint8_t range_hash[1024]
Hash table mapping upper byte to approximate symbol.
Definition: lagarithrac.h:54
common internal and external API header
unsigned hash_shift
Number of bits to shift to calculate hash for radix search.
Definition: lagarithrac.h:44
static void lag_rac_refill(lag_rac *l)
Definition: lagarithrac.h:60
unsigned low
Definition: lagarithrac.h:41
unsigned range
Definition: lagarithrac.h:42
void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length)
Definition: lagarithrac.c:33
const uint8_t * bytestream
Current position in input bytestream.
Definition: lagarithrac.h:47