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 */
26
27#ifndef AVCODEC_RANGECODER_H
28#define AVCODEC_RANGECODER_H
29
30#include <stdint.h>
31
32#include "libavutil/avassert.h"
33#include "libavutil/intmath.h"
34
35typedef struct RangeCoder {
36    int low;
37    int range;
38    int outstanding_count;
39    int outstanding_byte;
40    uint8_t zero_state[256];
41    uint8_t one_state[256];
42    uint8_t *bytestream_start;
43    uint8_t *bytestream;
44    uint8_t *bytestream_end;
45    int overread;
46#define MAX_OVERREAD 2
47} RangeCoder;
48
49void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
50void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
51
52/**
53 * Terminates the range coder
54 * @param version version 0 requires the decoder to know the data size in bytes
55 *                version 1 needs about 1 bit more space but does not need to
56 *                          carry the size from encoder to decoder
57 */
58int ff_rac_terminate(RangeCoder *c, int version);
59
60void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
61
62static inline void renorm_encoder(RangeCoder *c)
63{
64    // FIXME: optimize
65    while (c->range < 0x100) {
66        if (c->outstanding_byte < 0) {
67            c->outstanding_byte = c->low >> 8;
68        } else if (c->low <= 0xFF00) {
69            *c->bytestream++ = c->outstanding_byte;
70            for (; c->outstanding_count; c->outstanding_count--)
71                *c->bytestream++ = 0xFF;
72            c->outstanding_byte = c->low >> 8;
73        } else if (c->low >= 0x10000) {
74            *c->bytestream++ = c->outstanding_byte + 1;
75            for (; c->outstanding_count; c->outstanding_count--)
76                *c->bytestream++ = 0x00;
77            c->outstanding_byte = (c->low >> 8) & 0xFF;
78        } else {
79            c->outstanding_count++;
80        }
81
82        c->low     = (c->low & 0xFF) << 8;
83        c->range <<= 8;
84    }
85}
86
87static inline int get_rac_count(RangeCoder *c)
88{
89    int x = c->bytestream - c->bytestream_start + c->outstanding_count;
90    if (c->outstanding_byte >= 0)
91        x++;
92    return 8 * x - av_log2(c->range);
93}
94
95static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
96{
97    int range1 = (c->range * (*state)) >> 8;
98
99    av_assert2(*state);
100    av_assert2(range1 < c->range);
101    av_assert2(range1 > 0);
102    if (!bit) {
103        c->range -= range1;
104        *state    = c->zero_state[*state];
105    } else {
106        c->low  += c->range - range1;
107        c->range = range1;
108        *state   = c->one_state[*state];
109    }
110
111    renorm_encoder(c);
112}
113
114static inline void refill(RangeCoder *c)
115{
116    if (c->range < 0x100) {
117        c->range <<= 8;
118        c->low   <<= 8;
119        if (c->bytestream < c->bytestream_end) {
120            c->low += c->bytestream[0];
121            c->bytestream++;
122        } else
123            c->overread ++;
124    }
125}
126
127static inline int get_rac(RangeCoder *c, uint8_t *const state)
128{
129    int range1 = (c->range * (*state)) >> 8;
130
131    c->range -= range1;
132    if (c->low < c->range) {
133        *state = c->zero_state[*state];
134        refill(c);
135        return 0;
136    } else {
137        c->low  -= c->range;
138        *state   = c->one_state[*state];
139        c->range = range1;
140        refill(c);
141        return 1;
142    }
143}
144
145#endif /* AVCODEC_RANGECODER_H */
146