47 lines
1.0 KiB
C
47 lines
1.0 KiB
C
|
|
#include <math.h>
|
|
|
|
void drealft(double data[], unsigned long n, int isign)
|
|
{
|
|
void dfour1(double data[], unsigned long nn, int isign);
|
|
unsigned long i,i1,i2,i3,i4,np3;
|
|
double c1=0.5,c2,h1r,h1i,h2r,h2i;
|
|
double wr,wi,wpr,wpi,wtemp,theta;
|
|
|
|
theta=3.141592653589793/(double) (n>>1);
|
|
if (isign == 1) {
|
|
c2 = -0.5;
|
|
dfour1(data,n>>1,1);
|
|
} else {
|
|
c2=0.5;
|
|
theta = -theta;
|
|
}
|
|
wtemp=sin(0.5*theta);
|
|
wpr = -2.0*wtemp*wtemp;
|
|
wpi=sin(theta);
|
|
wr=1.0+wpr;
|
|
wi=wpi;
|
|
np3=n+3;
|
|
for (i=2;i<=(n>>2);i++) {
|
|
i4=1+(i3=np3-(i2=1+(i1=i+i-1)));
|
|
h1r=c1*(data[i1]+data[i3]);
|
|
h1i=c1*(data[i2]-data[i4]);
|
|
h2r = -c2*(data[i2]+data[i4]);
|
|
h2i=c2*(data[i1]-data[i3]);
|
|
data[i1]=h1r+wr*h2r-wi*h2i;
|
|
data[i2]=h1i+wr*h2i+wi*h2r;
|
|
data[i3]=h1r-wr*h2r+wi*h2i;
|
|
data[i4] = -h1i+wr*h2i+wi*h2r;
|
|
wr=(wtemp=wr)*wpr-wi*wpi+wr;
|
|
wi=wi*wpr+wtemp*wpi+wi;
|
|
}
|
|
if (isign == 1) {
|
|
data[1] = (h1r=data[1])+data[2];
|
|
data[2] = h1r-data[2];
|
|
} else {
|
|
data[1]=c1*((h1r=data[1])+data[2]);
|
|
data[2]=c1*(h1r-data[2]);
|
|
dfour1(data,n>>1,-1);
|
|
}
|
|
}
|