ftp.nice.ch/pub/next/developer/hardware/dsp/DSPFFT.N.bsa.tar.gz#/DSPFFT/test.c

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//Modified from Numerical Recipies in C
#include <math.h>
#import <stdio.h>
#import <stdlib.h>
#import <sys/time.h>

#define SWAP(a,b) tempr=(a);(a)=(b);(b)=tempr
void four1(data,nn,isign)
float data[];
int nn,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


main(){
	float qq[5000];
	int n,i;
	double total_time;
     struct timeval tp1, tp2;
     struct timezone tzp1, tzp2;
	for (n=16;n<=1024;n*=2){
		gettimeofday(&tp1, &tzp1);		// Time the command
	
	for(i=0;i<1000;i++){
		four1(qq,n,1);
	}
		gettimeofday(&tp2, &tzp2);
		total_time=tp2.tv_sec-tp1.tv_sec+(tp2.tv_usec-tp1.tv_usec)/1000000.0;
		printf("Total Elapsed time for %d points: %f seconds\n",n, total_time);
		}
}

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