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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 | ||
30 | static 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 | ||
45 | static 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 | ||
71 | void 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 | ||
81 | int 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 | } |