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#include <string.h>
34
35#include "libavutil/attributes.h"
36#include "libavutil/avassert.h"
37#include "libavutil/bswap.h"
38#include "libavutil/intreadwrite.h"
39
40#include "rangecoder.h"
41
42av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
43{
44    c->bytestream_start  =
45    c->bytestream        = buf;
46    c->bytestream_end    = buf + buf_size;
47    c->low               = 0;
48    c->range             = 0xFF00;
49    c->outstanding_count = 0;
50    c->outstanding_byte  = -1;
51}
52
53av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf,
54                                   int buf_size)
55{
56    /* cast to avoid compiler warning */
57    ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
58
59    c->low         = AV_RB16(c->bytestream);
60    c->bytestream += 2;
61    c->overread    = 0;
62    if (c->low >= 0xFF00) {
63        c->low = 0xFF00;
64        c->bytestream_end = c->bytestream;
65    }
66}
67
68void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
69{
70    const int64_t one = 1LL << 32;
71    int64_t p;
72    int last_p8, p8, i;
73
74    memset(c->zero_state, 0, sizeof(c->zero_state));
75    memset(c->one_state, 0, sizeof(c->one_state));
76
77    last_p8 = 0;
78    p       = one / 2;
79    for (i = 0; i < 128; i++) {
80        p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
81        if (p8 <= last_p8)
82            p8 = last_p8 + 1;
83        if (last_p8 && last_p8 < 256 && p8 <= max_p)
84            c->one_state[last_p8] = p8;
85
86        p      += ((one - p) * factor + one / 2) >> 32;
87        last_p8 = p8;
88    }
89
90    for (i = 256 - max_p; i <= max_p; i++) {
91        if (c->one_state[i])
92            continue;
93
94        p  = (i * one + 128) >> 8;
95        p += ((one - p) * factor + one / 2) >> 32;
96        p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
97        if (p8 <= i)
98            p8 = i + 1;
99        if (p8 > max_p)
100            p8 = max_p;
101        c->one_state[i] = p8;
102    }
103
104    for (i = 1; i < 255; i++)
105        c->zero_state[i] = 256 - c->one_state[256 - i];
106}
107
108/* Return the number of bytes written. */
109int ff_rac_terminate(RangeCoder *c, int version)
110{
111    if (version == 1)
112        put_rac(c, (uint8_t[]) { 129 }, 0);
113    c->range = 0xFF;
114    c->low  += 0xFF;
115    renorm_encoder(c);
116    c->range = 0xFF;
117    renorm_encoder(c);
118
119    av_assert1(c->low   == 0);
120    av_assert1(c->range >= 0x100);
121
122    return c->bytestream - c->bytestream_start;
123}
124