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rangecoder.c
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1 /*
2  * Range coder
3  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 /**
23  * @file
24  * Range coder.
25  * based upon
26  * "Range encoding: an algorithm for removing redundancy from a digitised
27  * message.
28  * G. N. N. Martin Presented in March 1979 to the Video &
29  * Data Recording Conference,
30  * IBM UK Scientific Center held in Southampton July 24-27 1979."
31  *
32  */
33 
34 #include <string.h>
35 
36 #include "libavutil/attributes.h"
37 #include "libavutil/avassert.h"
38 #include "libavutil/intreadwrite.h"
39 
40 #include "avcodec.h"
41 #include "rangecoder.h"
42 
44 {
45  c->bytestream_start =
46  c->bytestream = buf;
47  c->bytestream_end = buf + buf_size;
48  c->low = 0;
49  c->range = 0xFF00;
50  c->outstanding_count = 0;
51  c->outstanding_byte = -1;
52 }
53 
55  int buf_size)
56 {
57  /* cast to avoid compiler warning */
58  ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
59 
60  c->low = AV_RB16(c->bytestream);
61  c->bytestream += 2;
62 }
63 
64 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
65 {
66  const int64_t one = 1LL << 32;
67  int64_t p;
68  int last_p8, p8, i;
69 
70  memset(c->zero_state, 0, sizeof(c->zero_state));
71  memset(c->one_state, 0, sizeof(c->one_state));
72 
73  last_p8 = 0;
74  p = one / 2;
75  for (i = 0; i < 128; i++) {
76  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
77  if (p8 <= last_p8)
78  p8 = last_p8 + 1;
79  if (last_p8 && last_p8 < 256 && p8 <= max_p)
80  c->one_state[last_p8] = p8;
81 
82  p += ((one - p) * factor + one / 2) >> 32;
83  last_p8 = p8;
84  }
85 
86  for (i = 256 - max_p; i <= max_p; i++) {
87  if (c->one_state[i])
88  continue;
89 
90  p = (i * one + 128) >> 8;
91  p += ((one - p) * factor + one / 2) >> 32;
92  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
93  if (p8 <= i)
94  p8 = i + 1;
95  if (p8 > max_p)
96  p8 = max_p;
97  c->one_state[i] = p8;
98  }
99 
100  for (i = 1; i < 255; i++)
101  c->zero_state[i] = 256 - c->one_state[256 - i];
102 }
103 
104 /* Return the number of bytes written. */
106 {
107  c->range = 0xFF;
108  c->low += 0xFF;
109  renorm_encoder(c);
110  c->range = 0xFF;
111  renorm_encoder(c);
112 
113  av_assert1(c->low == 0);
114  av_assert1(c->range >= 0x100);
115 
116  return c->bytestream - c->bytestream_start;
117 }
118 
119 #ifdef TEST
120 #define SIZE 10240
121 
122 #include "libavutil/lfg.h"
123 #include "libavutil/log.h"
124 
125 static uint8_t b[9 * SIZE];
126 static uint8_t r[9 * SIZE];
127 
128 int main(void)
129 {
130  RangeCoder c;
131  int i;
132  uint8_t state[10];
133  AVLFG prng;
134 
135  av_lfg_init(&prng, 1);
136 
138  ff_build_rac_states(&c, (1LL << 32) / 20, 128 + 64 + 32 + 16);
139 
140  memset(state, 128, sizeof(state));
141 
142  for (i = 0; i < SIZE; i++)
143  r[i] = av_lfg_get(&prng) % 7;
144 
145  for (i = 0; i < SIZE; i++)
146  put_rac(&c, state, r[i] & 1);
147 
148  ff_rac_terminate(&c);
149 
150  ff_init_range_decoder(&c, b, SIZE);
151 
152  memset(state, 128, sizeof(state));
153 
154  for (i = 0; i < SIZE; i++)
155  if ((r[i] & 1) != get_rac(&c, state)) {
156  av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
157  return 1;
158  }
159 
160  return 0;
161 }
162 #endif /* TEST */
Definition: lfg.h:25
#define NULL
Definition: coverity.c:32
uint32_t low
Definition: mss3.c:64
uint8_t zero_state[256]
Definition: rangecoder.h:40
Range coder.
uint8_t * bytestream_end
Definition: rangecoder.h:44
const char * b
Definition: vf_curves.c:109
uint32_t range
Definition: mss3.c:64
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
uint8_t one_state[256]
Definition: rangecoder.h:41
Macro definitions for various function/variable attributes.
int ff_rac_terminate(RangeCoder *c)
Definition: rangecoder.c:105
uint8_t
#define av_cold
Definition: attributes.h:82
static int get_rac(RangeCoder *c, uint8_t *const state)
Definition: rangecoder.h:115
#define SIZE
Definition: golomb-test.c:31
#define av_log(a,...)
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:176
const char * r
Definition: vf_curves.c:107
static void renorm_encoder(RangeCoder *c)
Definition: rangecoder.h:52
simple assert() macros that are a bit more flexible than ISO C assert().
uint8_t * bytestream
Definition: rangecoder.h:43
#define av_assert1(cond)
assert() equivalent, that does not lie in speed critical code.
Definition: avassert.h:53
void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
Definition: rangecoder.c:64
int outstanding_byte
Definition: rangecoder.h:39
Libavcodec external API header.
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:38
void * buf
Definition: avisynth_c.h:553
av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
Definition: rangecoder.c:43
av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
Definition: rangecoder.c:54
static const int factor[16]
Definition: vf_pp7.c:75
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:30
static double c[64]
int outstanding_count
Definition: rangecoder.h:38
#define put_rac(C, S, B)
uint8_t * bytestream_start
Definition: rangecoder.h:42
static struct @205 state
int main(int argc, char **argv)
Definition: main.c:22