Zsinft.cin
// zsinft.cin is complex double routine for evaluation of the discrete sin transform (dsft)
// The routine below is suppoesed to be compiled together with routines zfour1.cin and zrealft.cin
#include <math.h>
void zsinft(z_type y[], int n)
{
void zrealft(z_type data[], unsigned long n, int isign);
int j,n2=n+2;
z_type sum,y1,y2;
double theta,wi=0.0,wr=1.0,wpi,wpr,wtemp;
theta=M_PI/(double) n;
wtemp=sin((double)0.5*theta);
wpr = -2*wtemp*wtemp;
wpi=sin(theta);
y[1]=0.0;
for (j=2;j<=(n>>1)+1;j++) {
wr=(wtemp=wr)*wpr-wi*wpi+wr;
wi=wi*wpr+wtemp*wpi+wi;
y1=wi*(y[j]+y[n2-j]);
y2=0.5*(y[j]-y[n2-j]);
y[j]=y1+y2;
y[n2-j]=y1-y2;
}
zrealft(y,n,1);
y[1]*=0.5;
sum=y[2]=0.0;
for (j=1;j<=n-1;j+=2) {
sum += y[j];
y[j]=y[j+1];
y[j+1]=sum;
}
}