#include <math.h>#define SWAP(a,b) tempr=(a);(a)=(b);(b)=temprvoid dfour1(double data[], unsigned long nn, int isign){	unsigned long n,mmax,m,j,istep,i;	double wtemp,wr,wpr,wpi,wi,theta;	double 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=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