Libav
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 Libav.
6  *
7  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
34 #include <string.h>
35 
36 #include "libavutil/attributes.h"
37 #include "avcodec.h"
38 #include "rangecoder.h"
39 #include "bytestream.h"
40 
41 av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
42 {
43  c->bytestream_start =
44  c->bytestream = buf;
45  c->bytestream_end = buf + buf_size;
46  c->low = 0;
47  c->range = 0xFF00;
48  c->outstanding_count = 0;
49  c->outstanding_byte = -1;
50 }
51 
53  int buf_size)
54 {
55  /* cast to avoid compiler warning */
56  ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
57 
58  c->low = bytestream_get_be16(&c->bytestream);
59 }
60 
61 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
62 {
63  const int64_t one = 1LL << 32;
64  int64_t p;
65  int last_p8, p8, i;
66 
67  memset(c->zero_state, 0, sizeof(c->zero_state));
68  memset(c->one_state, 0, sizeof(c->one_state));
69 
70  last_p8 = 0;
71  p = one / 2;
72  for (i = 0; i < 128; i++) {
73  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
74  if (p8 <= last_p8)
75  p8 = last_p8 + 1;
76  if (last_p8 && last_p8 < 256 && p8 <= max_p)
77  c->one_state[last_p8] = p8;
78 
79  p += ((one - p) * factor + one / 2) >> 32;
80  last_p8 = p8;
81  }
82 
83  for (i = 256 - max_p; i <= max_p; i++) {
84  if (c->one_state[i])
85  continue;
86 
87  p = (i * one + 128) >> 8;
88  p += ((one - p) * factor + one / 2) >> 32;
89  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
90  if (p8 <= i)
91  p8 = i + 1;
92  if (p8 > max_p)
93  p8 = max_p;
94  c->one_state[i] = p8;
95  }
96 
97  for (i = 1; i < 255; i++)
98  c->zero_state[i] = 256 - c->one_state[256 - i];
99 }
100 
101 /* Return the number of bytes written. */
103 {
104  c->range = 0xFF;
105  c->low += 0xFF;
106  renorm_encoder(c);
107  c->range = 0xFF;
108  renorm_encoder(c);
109 
110  assert(c->low == 0);
111  assert(c->range >= 0x100);
112 
113  return c->bytestream - c->bytestream_start;
114 }
115 
116 #ifdef TEST
117 #define SIZE 10240
118 
119 #include "libavutil/lfg.h"
120 #include "libavutil/log.h"
121 
122 int main(void)
123 {
124  RangeCoder c;
125  uint8_t b[9 * SIZE];
126  uint8_t r[9 * SIZE];
127  int i;
128  uint8_t state[10];
129  AVLFG prng;
130 
131  av_lfg_init(&prng, 1);
132 
133  ff_init_range_encoder(&c, b, SIZE);
134  ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
135 
136  memset(state, 128, sizeof(state));
137 
138  for (i = 0; i < SIZE; i++)
139  r[i] = av_lfg_get(&prng) % 7;
140 
141  for (i = 0; i < SIZE; i++)
142  put_rac(&c, state, r[i] & 1);
143 
144  ff_rac_terminate(&c);
145 
146  ff_init_range_decoder(&c, b, SIZE);
147 
148  memset(state, 128, sizeof(state));
149 
150  for (i = 0; i < SIZE; i++)
151  if ((r[i] & 1) != get_rac(&c, state)) {
152  av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
153  return 1;
154  }
155 
156  return 0;
157 }
158 #endif /* TEST */