rlft3.c

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#include <math.h>

void rlft3(float ***data, float **speq, unsigned long nn1, unsigned long nn2,
	unsigned long nn3, int isign)
{
	void fourn(float data[], unsigned long nn[], int ndim, int isign);
	void nrerror(char error_text[]);
	unsigned long i1,i2,i3,j1,j2,j3,nn[4],ii3;
	double theta,wi,wpi,wpr,wr,wtemp;
	float c1,c2,h1r,h1i,h2r,h2i;

	if (1+&data[nn1][nn2][nn3]-&data[1][1][1] != nn1*nn2*nn3)
		nrerror("rlft3: problem with dimensions or contiguity of data array\n");
	c1=0.5;
	c2 = -0.5*isign;
	theta=isign*(6.28318530717959/nn3);
	wtemp=sin(0.5*theta);
	wpr = -2.0*wtemp*wtemp;
	wpi=sin(theta);
	nn[1]=nn1;
	nn[2]=nn2;
	nn[3]=nn3 >> 1;
	if (isign == 1) {
		fourn(&data[1][1][1]-1,nn,3,isign);
		for (i1=1;i1<=nn1;i1++)
			for (i2=1,j2=0;i2<=nn2;i2++) {
				speq[i1][++j2]=data[i1][i2][1];
				speq[i1][++j2]=data[i1][i2][2];
			}
	}
	for (i1=1;i1<=nn1;i1++) {
		j1=(i1 != 1 ? nn1-i1+2 : 1);
		wr=1.0;
		wi=0.0;
		for (ii3=1,i3=1;i3<=(nn3>>2)+1;i3++,ii3+=2) {
			for (i2=1;i2<=nn2;i2++) {
				if (i3 == 1) {
					j2=(i2 != 1 ? ((nn2-i2)<<1)+3 : 1);
					h1r=c1*(data[i1][i2][1]+speq[j1][j2]);
					h1i=c1*(data[i1][i2][2]-speq[j1][j2+1]);
					h2i=c2*(data[i1][i2][1]-speq[j1][j2]);
					h2r= -c2*(data[i1][i2][2]+speq[j1][j2+1]);
					data[i1][i2][1]=h1r+h2r;
					data[i1][i2][2]=h1i+h2i;
					speq[j1][j2]=h1r-h2r;
					speq[j1][j2+1]=h2i-h1i;
				} else {
					j2=(i2 != 1 ? nn2-i2+2 : 1);
					j3=nn3+3-(i3<<1);
					h1r=c1*(data[i1][i2][ii3]+data[j1][j2][j3]);
					h1i=c1*(data[i1][i2][ii3+1]-data[j1][j2][j3+1]);
					h2i=c2*(data[i1][i2][ii3]-data[j1][j2][j3]);
					h2r= -c2*(data[i1][i2][ii3+1]+data[j1][j2][j3+1]);
					data[i1][i2][ii3]=h1r+wr*h2r-wi*h2i;
					data[i1][i2][ii3+1]=h1i+wr*h2i+wi*h2r;
					data[j1][j2][j3]=h1r-wr*h2r+wi*h2i;
					data[j1][j2][j3+1]= -h1i+wr*h2i+wi*h2r;
				}
			}
			wr=(wtemp=wr)*wpr-wi*wpi+wr;
			wi=wi*wpr+wtemp*wpi+wi;
		}
	}
	if (isign == -1)
		fourn(&data[1][1][1]-1,nn,3,isign);
}