fft(고속 푸리에 변환) 소스인데요...이해가 잘 안갑니다...ㅜ.

=======dft.h============

typedef struct {
	double real, imag;
} COMPLEX;
#define PI 3.141592

void fft(COMPLEX *,int);
void ifft(COMPLEX *,int);
void dft(COMPLEX *,COMPLEX *,int);
void idft(COMPLEX *,COMPLEX *,int);
void rfft(double *,COMPLEX *,int);
void ham(COMPLEX *,int);
void han(COMPLEX *,int);
void triang(COMPLEX *,int);
void black(COMPLEX *,int);
void harris(COMPLEX *,int);
int log2(unsigned int);

=========dft.c==========

#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include "dft.h"

void fft(COMPLEX *x, int m)
{ 
	static COMPLEX *w; 
	static int mstore = 0;
	static int n = 1;
	COMPLEX u,temp,tm;
	COMPLEX *xi,*xip,*xj,*wptr;
	int i,j,k,l,le,windex;
	double arg,w_real,w_imag,wrecur_real,wrecur_imag,wtemp_real;
	if(m != mstore) {

		if(mstore != 0) free(w);
		mstore = m;
		if(m == 0) return; 
		n = 1 << m; 
		le = n/2; 

		w = (COMPLEX *) calloc(le-1,sizeof(COMPLEX));
		if(!w) {
			printf("\nUnable to allocate complex W array\n");
			exit(1);
		}

		arg = PI/le; 
		wrecur_real = w_real = cos(arg);
		wrecur_imag = w_imag = -sin(arg);
		xj = w;
		for (j = 1 ; j < le ; j++) {
			xj->real = (double)wrecur_real;
			xj->imag = (double)wrecur_imag;
			xj++;
			wtemp_real = wrecur_real*w_real - wrecur_imag*w_imag;
			wrecur_imag = wrecur_real*w_imag + wrecur_imag*w_real;
			wrecur_real = wtemp_real;
		}
	}

	le = n;
	windex = 1;
	for (l = 0 ; l < m ; l++) {
		le = le/2;

		for(i = 0 ; i < n ; i = i + 2*le) {
			xi = x + i;
			xip = xi + le;
			temp.real = xi->real + xip->real;
			temp.imag = xi->imag + xip->imag;
			xip->real = xi->real - xip->real;
			xip->imag = xi->imag - xip->imag;
			*xi = temp;
		}


		wptr = w + windex - 1;
		for (j = 1 ; j < le ; j++) {
			u = *wptr;
			for (i = j ; i < n ; i = i + 2*le) {
				xi = x + i;
				xip = xi + le;
				temp.real = xi->real + xip->real;
				temp.imag = xi->imag + xip->imag;
				tm.real = xi->real - xip->real;
				tm.imag = xi->imag - xip->imag; 
				xip->real = tm.real*u.real - tm.imag*u.imag;
				xip->imag = tm.real*u.imag + tm.imag*u.real;
				*xi = temp;
			}
			wptr = wptr + windex;
		}
		windex = 2*windex;
	} 

	j = 0;
	for (i = 1 ; i < (n-1) ; i++) {
		k = n/2;
		while(k <= j) {
			j = j - k;
			k = k/2;
		}
		j = j + k;
		if (i < j) {
			xi = x + i;
			xj = x + j;
			temp = *xj;
			*xj = *xi;
			*xi = temp;
		}
	}
}

main(){
	int i;
	COMPLEX com[1];
	fft(com,1);
	for(i=0;i<sizeof(com);i++)
		printf("%f\n",com[i].real);
}

이거 인데요.....
main() 함수는 제가 임의로 만든거구요....
도저히 이해가 안갑니다....
main()함수를 저렇게 하니까
16개의 데이터가 계산되어서 나오는데요...
무슨값이 계산되어서 나오는지 모르겠어요...
메인에서 입력해준것도 없는데요.....
이거하나로 벌써 며칠째인지....ㅜ.ㅜ
주석 좀 부탁드려요.....