3 * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
5 * This file is part of Libav.
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.
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.
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
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"
38 #include "rangecoder.h"
39 #include "bytestream.h"
41 av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
45 c->bytestream_end = buf + buf_size;
48 c->outstanding_count = 0;
49 c->outstanding_byte = -1;
52 av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf,
55 /* cast to avoid compiler warning */
56 ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
58 c->low = bytestream_get_be16(&c->bytestream);
61 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
63 const int64_t one = 1LL << 32;
67 memset(c->zero_state, 0, sizeof(c->zero_state));
68 memset(c->one_state, 0, sizeof(c->one_state));
72 for (i = 0; i < 128; i++) {
73 p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
76 if (last_p8 && last_p8 < 256 && p8 <= max_p)
77 c->one_state[last_p8] = p8;
79 p += ((one - p) * factor + one / 2) >> 32;
83 for (i = 256 - max_p; i <= max_p; i++) {
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
97 for (i = 1; i < 255; i++)
98 c->zero_state[i] = 256 - c->one_state[256 - i];
101 /* Return the number of bytes written. */
102 int ff_rac_terminate(RangeCoder *c)
111 assert(c->range >= 0x100);
113 return c->bytestream - c->bytestream_start;
119 #include "libavutil/lfg.h"
120 #include "libavutil/log.h"
131 av_lfg_init(&prng, 1);
133 ff_init_range_encoder(&c, b, SIZE);
134 ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
136 memset(state, 128, sizeof(state));
138 for (i = 0; i < SIZE; i++)
139 r[i] = av_lfg_get(&prng) % 7;
141 for (i = 0; i < SIZE; i++)
142 put_rac(&c, state, r[i] & 1);
144 ff_rac_terminate(&c);
146 ff_init_range_decoder(&c, b, SIZE);
148 memset(state, 128, sizeof(state));
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);