#include <math.h>
#include <stdio.h>

static float sqrarg;
#define SQR(a) (sqrarg=(a),sqrarg*sqrarg)

#define WINDOW(j,a,b) (1.0-fabs((((j)-1)-(a))*(b)))       /* Parzen */
/* #define WINDOW(j,a,b) 1.0 */                           /* Square */
/* #define WINDOW(j,a,b) (1.0-SQR((((j)-1)-(a))*(b))) */  /* Welch  */

void spctrm(fp,p,m,k,ovrlap)
FILE *fp;
float p[];
int m,k,ovrlap;
{
	int mm,m44,m43,m4,kk,joffn,joff,j2,j;
	float w,facp,facm,*w1,*w2,sumw=0.0,den=0.0;
	float *vector();
	void four1(),free_vector();

	mm=m+m;
	m43=(m4=mm+mm)+3;
	m44=m43+1;
	w1=vector(1,m4);
	w2=vector(1,m);
	facm=m-0.5;
	facp=1.0/(m+0.5);
	for (j=1;j<=mm;j++) sumw += SQR(WINDOW(j,facm,facp));
	for (j=1;j<=m;j++) p[j]=0.0;
	if (ovrlap)
		for (j=1;j<=m;j++) fscanf(fp,"%f",&w2[j]);
	for (kk=1;kk<=k;kk++) {
		for (joff = -1;joff<=0;joff++) {
			if (ovrlap) {
				for (j=1;j<=m;j++) w1[joff+j+j]=w2[j];
				for (j=1;j<=m;j++) fscanf(fp,"%f",&w2[j]);
				joffn=joff+mm;
				for (j=1;j<=m;j++) w1[joffn+j+j]=w2[j];
			} else {
				for (j=joff+2;j<=m4;j+=2)
					fscanf(fp,"%f",&w1[j]);
			}
		}
		for (j=1;j<=mm;j++) {
			j2=j+j;
			w=WINDOW(j,facm,facp);
			w1[j2] *= w;
			w1[j2-1] *= w;
		}
		four1(w1,mm,1);
		p[1] += (SQR(w1[1])+SQR(w1[2]));
		for (j=2;j<=m;j++) {
			j2=j+j;
			p[j] += (SQR(w1[j2])+SQR(w1[j2-1])
				+SQR(w1[m44-j2])+SQR(w1[m43-j2]));
		}
		den += sumw;
	}
	den *= m4;
	for (j=1;j<=m;j++) p[j] /= den;
	free_vector(w2,1,m);
	free_vector(w1,1,m4);
}

#undef SQR
#undef WINDOW