# Four1.cin

// I have converted the zsinft.cin from complex double to float. The result is below. it should be close to the original by the "numerical recipes", but I cannot access the original to check this.

//The routine below is float implementation of the sin fourier transform (FSFT. It is supposed to be compiled together with four1.cin and realft.cin

#define SWAP(a,b) tempr=(a);(a)=(b);(b)=tempr

void four1(float data[], unsigned long nn, int isign)
{
unsigned long n,mmax,m,j,istep,i;
float wtemp,wr,wpr,wpi,wi,theta; //double
float tempr,tempi; // ztype

n=nn << 1;
j=1;
for (i=1;i<n;i+=2) {
if (j > i) {
SWAP(data[j],data[i]);
SWAP(data[j+1],data[i+1]);
}
m=n >> 1;
while (m >= 2 && j > m) {
j -= m;
m >>= 1;
}
j += m;
}
mmax=2;
while (n > mmax) {
istep=mmax << 1;
theta=isign*(6.28318530717959/mmax);
wtemp=sin(0.5*theta);
wpr = -2.0*wtemp*wtemp;
wpi=sin(theta);
wr=1.0;
wi=0.0;
for (m=1;m<mmax;m+=2) {
for (i=m;i<=n;i+=istep) {
j=i+mmax;
tempr=wr*data[j]-wi*data[j+1];
tempi=wr*data[j+1]+wi*data[j];
data[j]=data[i]-tempr;
data[j+1]=data[i+1]-tempi;
data[i] += tempr;
data[i+1] += tempi;
}
wr=(wtemp=wr)*wpr-wi*wpi+wr;
wi=wi*wpr+wtemp*wpi+wi;
}
mmax=istep;
}
}
#undef SWAP