1/*
2 * MQ-coder decoder
3 * Copyright (c) 2007 Kamil Nowosad
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 * MQ-coder decoder
24 * @file
25 * @author Kamil Nowosad
26 */
27
28#include "mqc.h"
29
30static void bytein(MqcState *mqc)
31{
32    if (*mqc->bp == 0xff) {
33        if (*(mqc->bp + 1) > 0x8f)
34            mqc->c++;
35        else {
36            mqc->bp++;
37            mqc->c += 2 + 0xfe00 - (*mqc->bp << 9);
38        }
39    } else {
40        mqc->bp++;
41        mqc->c += 1 + 0xff00 - (*mqc->bp << 8);
42    }
43}
44
45static int exchange(MqcState *mqc, uint8_t *cxstate, int lps)
46{
47    int d;
48    if ((mqc->a < ff_mqc_qe[*cxstate]) ^ (!lps)) {
49        if (lps)
50            mqc->a = ff_mqc_qe[*cxstate];
51        d = *cxstate & 1;
52        *cxstate = ff_mqc_nmps[*cxstate];
53    } else {
54        if (lps)
55            mqc->a = ff_mqc_qe[*cxstate];
56        d = 1 - (*cxstate & 1);
57        *cxstate = ff_mqc_nlps[*cxstate];
58    }
59    // do RENORMD: see ISO/IEC 15444-1:2002 ��C.3.3
60    do {
61        if (!(mqc->c & 0xff)) {
62            mqc->c -= 0x100;
63            bytein(mqc);
64        }
65        mqc->a += mqc->a;
66        mqc->c += mqc->c;
67    } while (!(mqc->a & 0x8000));
68    return d;
69}
70
71void ff_mqc_initdec(MqcState *mqc, uint8_t *bp)
72{
73    ff_mqc_init_contexts(mqc);
74    mqc->bp = bp;
75    mqc->c  = (*mqc->bp ^ 0xff) << 16;
76    bytein(mqc);
77    mqc->c = mqc->c << 7;
78    mqc->a = 0x8000;
79}
80
81int ff_mqc_decode(MqcState *mqc, uint8_t *cxstate)
82{
83    mqc->a -= ff_mqc_qe[*cxstate];
84    if ((mqc->c >> 16) < mqc->a) {
85        if (mqc->a & 0x8000)
86            return *cxstate & 1;
87        else
88            return exchange(mqc, cxstate, 0);
89    } else {
90        mqc->c -= mqc->a << 16;
91        return exchange(mqc, cxstate, 1);
92    }
93}
94