Realft.cin

// realft.cin is conversion of routine zrealft.cin from complex double to float, // as I could not access the original. I hope, it is close to the original from the Numerical recipes and does exactly the same.

void realft(float data[], unsigned long n, int isign) { /* void zfour1(z_type data[], unsigned long nn, int isign);*/ unsigned long i,i1,i2,i3,i4,np3; float c1=0.5,c2,h1r,h1i,h2r,h2i; //z_type float wr,wi,wpr,wpi,wtemp,theta; //double

theta=M_PI/(float) (n>>1); if (isign == 1) { c2 = -(float)0.5; four1(data,n>>1,1); } else { c2=(float)0.5; theta = -theta; }       wtemp=sin((float)0.5*theta); wpr = -(float)2.0*wtemp*wtemp; wpi=sin(theta); wr=(float)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]); four1(data,n>>1,-1); } }

Keywords
Fourier transform, sinft, DSFT]], cosft, DCFT]]