realft.c

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#include "../sms.h"

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

static void four1(float *data, int nn, int isign)
{
	int n,mmax,m,j,istep,i;
	double wtemp,wr,wpr,wpi,wi,theta;
	float tempr,tempi;

	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=2*mmax;
		theta=6.28318530717959/(isign*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

void realft(float *data, int n, int isign)
{
	int i,i1,i2,i3,i4,n2p3;
	float c1=0.5,c2,h1r,h1i,h2r,h2i;
	double wr,wi,wpr,wpi,wtemp,theta;

	theta=3.141592653589793/(double) n;
	if (isign == 1) {
		c2 = -0.5;
		four1(data,n,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;
	n2p3=2*n+3;
	for (i=2;i<=n/2;i++) {
		i4=1+(i3=n2p3-(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);
	}
}

These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.