FFmpeg
mqcdec.c
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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, int raw, int reset)
72 {
73  mqc->raw = raw;
74  if (reset)
76  mqc->bp = bp;
77  mqc->c = (*mqc->bp ^ 0xff) << 16;
78  bytein(mqc);
79  mqc->c = mqc->c << 7;
80  mqc->a = 0x8000;
81 }
82 
83 static int mqc_decode_bypass(MqcState *mqc) {
84  int bit = !(mqc->c & 0x40000000);
85  if (!(mqc->c & 0xff)) {
86  mqc->c -= 0x100;
87  bytein(mqc);
88  }
89  mqc->c += mqc->c;
90  return bit;
91 }
92 
93 int ff_mqc_decode(MqcState *mqc, uint8_t *cxstate)
94 {
95  if (mqc->raw)
96  return mqc_decode_bypass(mqc);
97  mqc->a -= ff_mqc_qe[*cxstate];
98  if ((mqc->c >> 16) < mqc->a) {
99  if (mqc->a & 0x8000)
100  return *cxstate & 1;
101  else
102  return exchange(mqc, cxstate, 0);
103  } else {
104  mqc->c -= mqc->a << 16;
105  return exchange(mqc, cxstate, 1);
106  }
107 }
void ff_mqc_init_contexts(MqcState *mqc)
MQ-coder context initialisations.
Definition: mqc.c:111
static int mqc_decode_bypass(MqcState *mqc)
Definition: mqcdec.c:83
MQ-coder.
static void bytein(MqcState *mqc)
Definition: mqcdec.c:30
uint8_t
int ff_mqc_decode(MqcState *mqc, uint8_t *cxstate)
MQ decoder.
Definition: mqcdec.c:93
uint16_t ff_mqc_qe[2 *47]
Definition: mqc.c:93
void ff_mqc_initdec(MqcState *mqc, uint8_t *bp, int raw, int reset)
Initialize MQ-decoder.
Definition: mqcdec.c:71
uint8_t ff_mqc_nlps[2 *47]
Definition: mqc.c:94
unsigned int a
Definition: mqc.h:42
uint8_t ff_mqc_nmps[2 *47]
Definition: mqc.c:95
unsigned int c
Definition: mqc.h:43
static int exchange(MqcState *mqc, uint8_t *cxstate, int lps)
Definition: mqcdec.c:45
#define bit(string, value)
Definition: cbs_mpeg2.c:58
int raw
Definition: mqc.h:46
Definition: mqc.h:40
uint8_t * bp
Definition: mqc.h:41