summaryrefslogtreecommitdiffstats
path: root/libavcodec/dirac_arith.h
blob: b605825027a82db538c278ba04e3fe225b90f908 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
/*
 * Copyright (C) 2007 Marco Gerards <marco@gnu.org>
 * Copyright (C) 2009 David Conrad
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * Arithmetic decoder for Dirac
 * @author Marco Gerards <marco@gnu.org>
 */

#ifndef AVCODEC_DIRAC_ARITH_H
#define AVCODEC_DIRAC_ARITH_H

#include "bytestream.h"
#include "get_bits.h"

enum dirac_arith_contexts {
    CTX_ZPZN_F1,
    CTX_ZPNN_F1,
    CTX_NPZN_F1,
    CTX_NPNN_F1,
    CTX_ZP_F2,
    CTX_ZP_F3,
    CTX_ZP_F4,
    CTX_ZP_F5,
    CTX_ZP_F6,
    CTX_NP_F2,
    CTX_NP_F3,
    CTX_NP_F4,
    CTX_NP_F5,
    CTX_NP_F6,
    CTX_COEFF_DATA,
    CTX_SIGN_NEG,
    CTX_SIGN_ZERO,
    CTX_SIGN_POS,
    CTX_ZERO_BLOCK,
    CTX_DELTA_Q_F,
    CTX_DELTA_Q_DATA,
    CTX_DELTA_Q_SIGN,

    DIRAC_CTX_COUNT
};

// Dirac resets the arith decoder between decoding various types of data,
// so many contexts are never used simultaneously. Thus, we can reduce
// the number of contexts needed by reusing them.
#define CTX_SB_F1        CTX_ZP_F5
#define CTX_SB_DATA      0
#define CTX_PMODE_REF1   0
#define CTX_PMODE_REF2   1
#define CTX_GLOBAL_BLOCK 2
#define CTX_MV_F1        CTX_ZP_F2
#define CTX_MV_DATA      0
#define CTX_DC_F1        CTX_ZP_F5
#define CTX_DC_DATA      0

typedef struct {
    unsigned low;
    uint16_t range;
    int16_t  counter;

    const uint8_t *bytestream;
    const uint8_t *bytestream_end;

    uint16_t contexts[DIRAC_CTX_COUNT];
} DiracArith;

extern const uint8_t ff_dirac_next_ctx[DIRAC_CTX_COUNT];
extern const uint16_t ff_dirac_prob[256];
extern int16_t ff_dirac_prob_branchless[256][2];

static inline void renorm(DiracArith *c)
{
#if HAVE_FAST_CLZ
    int shift = 14 - av_log2_16bit(c->range-1) + ((c->range-1)>>15);

    c->low    <<= shift;
    c->range  <<= shift;
    c->counter += shift;
#else
    while (c->range <= 0x4000) {
        c->low   <<= 1;
        c->range <<= 1;
        c->counter++;
    }
#endif
}

static inline void refill(DiracArith *c)
{
    int counter = c->counter;

    if (counter >= 0) {
        int new = bytestream_get_be16(&c->bytestream);

        // the spec defines overread bits to be 1, and streams rely on this
        if (c->bytestream > c->bytestream_end) {
            new |= 0xff;
            if (c->bytestream > c->bytestream_end+1)
                new |= 0xff00;

            c->bytestream = c->bytestream_end;
        }

        c->low += new << counter;
        counter -= 16;
    }
    c->counter = counter;
}

static inline int dirac_get_arith_bit(DiracArith *c, int ctx)
{
    int prob_zero = c->contexts[ctx];
    int range_times_prob, bit;
    unsigned low = c->low;
    int    range = c->range;

    range_times_prob = (c->range * prob_zero) >> 16;

#if HAVE_FAST_CMOV
    low   -= range_times_prob << 16;
    range -= range_times_prob;
    bit = 0;
    __asm__(
        "cmpl   %5, %4 \n\t"
        "setae  %b0    \n\t"
        "cmovb  %3, %2 \n\t"
        "cmovb  %5, %1 \n\t"
        : "+q"(bit), "+r"(range), "+r"(low)
        : "r"(c->low), "r"(c->low>>16),
          "r"(range_times_prob)
    );
#else
    bit = (low >> 16) >= range_times_prob;
    if (bit) {
        low   -= range_times_prob << 16;
        range -= range_times_prob;
    } else {
        range  = range_times_prob;
    }
#endif

    c->contexts[ctx] += ff_dirac_prob_branchless[prob_zero>>8][bit];
    c->low   = low;
    c->range = range;

    renorm(c);
    refill(c);
    return bit;
}

static inline int dirac_get_arith_uint(DiracArith *c, int follow_ctx, int data_ctx)
{
    int ret = 1;
    while (!dirac_get_arith_bit(c, follow_ctx)) {
        ret <<= 1;
        ret += dirac_get_arith_bit(c, data_ctx);
        follow_ctx = ff_dirac_next_ctx[follow_ctx];
    }
    return ret-1;
}

static inline int dirac_get_arith_int(DiracArith *c, int follow_ctx, int data_ctx)
{
    int ret = dirac_get_arith_uint(c, follow_ctx, data_ctx);
    if (ret && dirac_get_arith_bit(c, data_ctx+1))
        ret = -ret;
    return ret;
}

void ff_dirac_init_arith_decoder(DiracArith *c, GetBitContext *gb, int length);

#endif /* AVCODEC_DIRAC_ARITH_H */
OpenPOWER on IntegriCloud