1 /* MPEG/WAVE Sound library
2
3 (C) 1997 by Jung woo-jae */
4
5 // Mpeglayer1.cc
6 // It's for MPEG Layer 1
7
8 #ifdef HAVE_CONFIG_H
9 #include "config.h"
10 #endif
11
12 #include "MPEGaudio.h"
13 #if defined(_WIN32) && defined(_MSC_VER)
14 // disable warnings about double to float conversions
15 #pragma warning(disable: 4244 4305)
16 #endif
17
18 // Tables for layer 1
19 static const REAL factortable[15] =
20 {
21 0.0,
22 (1.0/2.0) * (4.0/3.0), (1.0/4.0) * (8.0/7.0),
23 (1.0/8.0) * (16.0/15.0), (1.0/16.0) * (32.0/31.0),
24 (1.0/32.0) * (64.0/63.0), (1.0/64.0) * (128.0/127.0),
25 (1.0/128.0) * (256.0/255.0), (1.0/256.0) * (512.0/511.0),
26 (1.0/512.0) * (1024.0/1023.0), (1.0/1024.0) * (2048.0/2047.0),
27 (1.0/2048.0) * (4096.0/4095.0), (1.0/4096.0) * (8192.0/8191.0),
28 (1.0/8192.0) * (16384.0/16383.0), (1.0/16384.0) * (32768.0/32767.0)
29 };
30
31 static const REAL offsettable[15] =
32 {
33 0.0,
34 ((1.0/2.0)-1.0) * (4.0/3.0), ((1.0/4.0)-1.0) * (8.0/7.0),
35 ((1.0/8.0)-1.0) * (16.0/15.0), ((1.0/16.0)-1.0) * (32.0/31.0),
36 ((1.0/32.0)-1.0) * (64.0/63.0), ((1.0/64.0)-1.0) * (128.0/127.0),
37 ((1.0/128.0)-1.0) * (256.0/255.0), ((1.0/256.0)-1.0) * (512.0/511.0),
38 ((1.0/512.0)-1.0) * (1024.0/1023.0), ((1.0/1024.0)-1.0) * (2048.0/2047.0),
39 ((1.0/2048.0)-1.0) * (4096.0/4095.0), ((1.0/4096.0)-1.0) * (8192.0/8191.0),
40 ((1.0/8192.0)-1.0) * (16384.0/16383.0), ((1.0/16384.0)-1.0) * (32768.0/32767.0)
41 };
42
43 // Mpeg layer 1
extractlayer1(void)44 void MPEGaudio::extractlayer1(void)
45 {
46 REAL fraction[MAXCHANNEL][MAXSUBBAND];
47 REAL scalefactor[MAXCHANNEL][MAXSUBBAND];
48
49 int bitalloc[MAXCHANNEL][MAXSUBBAND],
50 sample[MAXCHANNEL][MAXSUBBAND];
51
52 register int i,j;
53 int s=stereobound,l;
54
55
56 // Bitalloc
57 for(i=0;i<s;i++)
58 {
59 bitalloc[LS][i]=getbits(4);
60 bitalloc[RS][i]=getbits(4);
61 }
62 for(;i<MAXSUBBAND;i++)
63 bitalloc[LS][i]=
64 bitalloc[RS][i]=getbits(4);
65
66 // Scale index
67 if(inputstereo)
68 for(i=0;i<MAXSUBBAND;i++)
69 {
70 if(bitalloc[LS][i])scalefactor[LS][i]=scalefactorstable[getbits(6)];
71 if(bitalloc[RS][i])scalefactor[RS][i]=scalefactorstable[getbits(6)];
72 }
73 else
74 for(i=0;i<MAXSUBBAND;i++)
75 if(bitalloc[LS][i])scalefactor[LS][i]=scalefactorstable[getbits(6)];
76
77 for(l=0;l<SCALEBLOCK;l++)
78 {
79 // Sample
80 for(i=0;i<s;i++)
81 {
82 if((j=bitalloc[LS][i]))sample[LS][i]=getbits(j+1);
83 if((j=bitalloc[RS][i]))sample[RS][i]=getbits(j+1);
84 }
85 for(;i<MAXSUBBAND;i++)
86 if((j=bitalloc[LS][i]))sample[LS][i]=sample[RS][i]=getbits(j+1);
87
88
89 // Fraction
90 if(outputstereo)
91 for(i=0;i<MAXSUBBAND;i++)
92 {
93 if((j=bitalloc[LS][i]))
94 fraction[LS][i]=(REAL(sample[LS][i])*factortable[j]+offsettable[j])
95 *scalefactor[LS][i];
96 else fraction[LS][i]=0.0;
97 if((j=bitalloc[RS][i]))
98 fraction[RS][i]=(REAL(sample[RS][i])*factortable[j]+offsettable[j])
99 *scalefactor[RS][i];
100 else fraction[RS][i]=0.0;
101 }
102 else
103 for(i=0;i<MAXSUBBAND;i++)
104 if((j=bitalloc[LS][i]))
105 fraction[LS][i]=(REAL(sample[LS][i])*factortable[j]+offsettable[j])
106 *scalefactor[LS][i];
107 else fraction[LS][i]=0.0;
108
109 subbandsynthesis(fraction[LS],fraction[RS]);
110 }
111 }
112