3 * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
5 * This file is part of FFmpeg.
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.
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.
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
26 * "Range encoding: an algorithm for removing redundancy from a digitised
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."
36 #include "libavutil/attributes.h"
37 #include "libavutil/avassert.h"
38 #include "libavutil/intreadwrite.h"
41 #include "rangecoder.h"
43 av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
47 c->bytestream_end = buf + buf_size;
50 c->outstanding_count = 0;
51 c->outstanding_byte = -1;
54 av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf,
57 /* cast to avoid compiler warning */
58 ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
60 c->low = AV_RB16(c->bytestream);
64 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
66 const int64_t one = 1LL << 32;
70 memset(c->zero_state, 0, sizeof(c->zero_state));
71 memset(c->one_state, 0, sizeof(c->one_state));
75 for (i = 0; i < 128; i++) {
76 p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
79 if (last_p8 && last_p8 < 256 && p8 <= max_p)
80 c->one_state[last_p8] = p8;
82 p += ((one - p) * factor + one / 2) >> 32;
86 for (i = 256 - max_p; i <= max_p; i++) {
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
100 for (i = 1; i < 255; i++)
101 c->zero_state[i] = 256 - c->one_state[256 - i];
104 /* Return the number of bytes written. */
105 int ff_rac_terminate(RangeCoder *c)
113 av_assert1(c->low == 0);
114 av_assert1(c->range >= 0x100);
116 return c->bytestream - c->bytestream_start;
122 #include "libavutil/lfg.h"
123 #include "libavutil/log.h"
125 static uint8_t b[9 * SIZE];
126 static uint8_t r[9 * SIZE];
135 av_lfg_init(&prng, 1);
137 ff_init_range_encoder(&c, b, SIZE);
138 ff_build_rac_states(&c, (1LL << 32) / 20, 128 + 64 + 32 + 16);
140 memset(state, 128, sizeof(state));
142 for (i = 0; i < SIZE; i++)
143 r[i] = av_lfg_get(&prng) % 7;
145 for (i = 0; i < SIZE; i++)
146 put_rac(&c, state, r[i] & 1);
148 ff_rac_terminate(&c);
150 ff_init_range_decoder(&c, b, SIZE);
152 memset(state, 128, sizeof(state));
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);