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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/avassert.h"
37 #include "avcodec.h"
38 #include "rangecoder.h"
39 #include "bytestream.h"
40 
41 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 
52 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
53 {
54  /* cast to avoid compiler warning */
55  ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
56 
57  c->low = bytestream_get_be16((const uint8_t **)&c->bytestream);
58 }
59 
60 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
61 {
62  const int64_t one = 1LL << 32;
63  int64_t p;
64  int last_p8, p8, i;
65 
66  memset(c->zero_state, 0, sizeof(c->zero_state));
67  memset(c->one_state, 0, sizeof(c->one_state));
68 
69  last_p8 = 0;
70  p = one / 2;
71  for (i = 0; i < 128; i++) {
72  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
73  if (p8 <= last_p8)
74  p8 = last_p8 + 1;
75  if (last_p8 && last_p8 < 256 && p8 <= max_p)
76  c->one_state[last_p8] = p8;
77 
78  p += ((one - p) * factor + one / 2) >> 32;
79  last_p8 = p8;
80  }
81 
82  for (i = 256 - max_p; i <= max_p; i++) {
83  if (c->one_state[i])
84  continue;
85 
86  p = (i * one + 128) >> 8;
87  p += ((one - p) * factor + one / 2) >> 32;
88  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
89  if (p8 <= i)
90  p8 = i + 1;
91  if (p8 > max_p)
92  p8 = max_p;
93  c->one_state[i] = p8;
94  }
95 
96  for (i = 1; i < 255; i++)
97  c->zero_state[i] = 256 - c->one_state[256 - i];
98 }
99 
100 /* Return the number of bytes written. */
102 {
103  c->range = 0xFF;
104  c->low += 0xFF;
105  renorm_encoder(c);
106  c->range = 0xFF;
107  renorm_encoder(c);
108 
109  av_assert1(c->low == 0);
110  av_assert1(c->range >= 0x100);
111 
112  return c->bytestream - c->bytestream_start;
113 }
114 
115 #ifdef TEST
116 #define SIZE 10240
117 
118 #include "libavutil/lfg.h"
119 #include "libavutil/log.h"
120 
121 int main(void)
122 {
123  RangeCoder c;
124  uint8_t b[9 * SIZE];
125  uint8_t r[9 * SIZE];
126  int i;
127  uint8_t state[10];
128  AVLFG prng;
129 
130  av_lfg_init(&prng, 1);
131 
132  ff_init_range_encoder(&c, b, SIZE);
133  ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
134 
135  memset(state, 128, sizeof(state));
136 
137  for (i = 0; i < SIZE; i++)
138  r[i] = av_lfg_get(&prng) % 7;
139 
140  for (i = 0; i < SIZE; i++)
141  put_rac(&c, state, r[i] & 1);
142 
143  ff_rac_terminate(&c);
144 
145  ff_init_range_decoder(&c, b, SIZE);
146 
147  memset(state, 128, sizeof(state));
148 
149  for (i = 0; i < SIZE; i++)
150  if ((r[i] & 1) != get_rac(&c, state)) {
151  av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
152  return 1;
153  }
154 
155  return 0;
156 }
157 #endif /* TEST */