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
191
192
193
194
195
196
|
/*
* Program: REALFFT.C
* Author: Philip VanBaren
* Date: 2 September 1993
*
* Description: These routines perform an FFT on real data.
* On a 486/33 compiled using Borland C++ 3.1 with full
* speed optimization and a small memory model, a 1024 point
* FFT takes about 16ms.
* This code is for integer data, but could be converted
* to float or double simply by changing the data types
* and getting rid of the bit-shifting necessary to prevent
* overflow/underflow in fixed-point calculations.
*
* Note: Output is BIT-REVERSED! so you must use the BitReversed to
* get legible output, (i.e. Real_i = buffer[ BitReversed[i] ]
* Imag_i = buffer[ BitReversed[i]+1 ] )
* Input is in normal order.
*
* Copyright (C) 1995 Philip VanBaren
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* For Borland C++/TASM you may define the flag ASMFFTCODE in order to use the
* assembly code for the FFT. This will skip the compilation of the C version
* of the routine; you must be sure to add realffta.asm to your makefile
*/
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include "soundfft.h"
int *BitReversed;
short *SinTable;
int Points = 0;
/*
* Initialize the Sine table and Twiddle pointers (bit-reversed pointers)
* for the FFT routine.
*/
void InitializeFFT(int fftlen)
{
int i;
int temp;
int mask;
/*
* FFT size is only half the number of data points
* The full FFT output can be reconstructed from this FFT's output.
* (This optimization can be made since the data is real.)
*/
Points = fftlen;
if((SinTable=(short *)malloc(Points*sizeof(short)))==NULL)
{
puts("Error allocating memory for Sine table.");
exit(1);
}
if((BitReversed=(int *)malloc(Points/2*sizeof(int)))==NULL)
{
puts("Error allocating memory for BitReversed.");
exit(1);
}
for(i=0;i<Points/2;i++)
{
temp=0;
for(mask=Points/4;mask>0;mask >>= 1)
temp=(temp >> 1) + (i&mask ? Points/2 : 0);
BitReversed[i]=temp;
}
for(i=0;i<Points/2;i++)
{
register double s,c;
s=floor(-32768.0*sin(2*M_PI*i/(Points))+0.5);
c=floor(-32768.0*cos(2*M_PI*i/(Points))+0.5);
if(s>32767.5) s=32767;
if(c>32767.5) c=32767;
SinTable[BitReversed[i] ]=(short)s;
SinTable[BitReversed[i]+1]=(short)c;
}
}
/*
* Free up the memory allotted for Sin table and Twiddle Pointers
*/
void EndFFT(void)
{
free(BitReversed);
free(SinTable);
Points=0;
}
/* Include this only if you don't use the REALFFTA.ASM routine */
/* This is for DOS only */
#ifndef ASMFFTCODE
short *A,*B;
short *sptr;
short *endptr1,*endptr2;
int *br1,*br2;
long HRplus,HRminus,HIplus,HIminus;
/*
* Actual FFT routine. Must call InitializeFFT(fftlen) first!
*/
void RealFFT(short *buffer)
{
int ButterfliesPerGroup=Points/4;
endptr1=buffer+Points;
/*
* Butterfly:
* Ain-----Aout
* \ /
* / \
* Bin-----Bout
*/
while(ButterfliesPerGroup>0)
{
A=buffer;
B=buffer+ButterfliesPerGroup*2;
sptr=SinTable;
while(A<endptr1)
{
register short sin=*sptr;
register short cos=*(sptr+1);
endptr2=B;
while(A<endptr2)
{
long v1=((long)*B*cos + (long)*(B+1)*sin) >> 15;
long v2=((long)*B*sin - (long)*(B+1)*cos) >> 15;
*B=(*A+v1)>>1;
*(A++)=*(B++)-v1;
*B=(*A-v2)>>1;
*(A++)=*(B++)+v2;
}
A=B;
B+=ButterfliesPerGroup*2;
sptr+=2;
}
ButterfliesPerGroup >>= 1;
}
/*
* Massage output to get the output for a real input sequence.
*/
br1=BitReversed+1;
br2=BitReversed+Points/2-1;
while(br1<=br2)
{
register long temp1,temp2;
short sin=SinTable[*br1];
short cos=SinTable[*br1+1];
A=buffer+*br1;
B=buffer+*br2;
HRplus = (HRminus = *A - *B ) + (*B << 1);
HIplus = (HIminus = *(A+1) - *(B+1)) + (*(B+1) << 1);
temp1 = ((long)sin*HRminus - (long)cos*HIplus) >> 15;
temp2 = ((long)cos*HRminus + (long)sin*HIplus) >> 15;
*B = (*A = (HRplus + temp1) >> 1) - temp1;
*(B+1) = (*(A+1) = (HIminus + temp2) >> 1) - HIminus;
br1++;
br2--;
}
/*
* Handle DC bin separately
*/
buffer[0]+=buffer[1];
buffer[1]=0;
}
#endif
|
