このプログラムでx2[i]y2[i]の絶対値の２乗がほしいんですけどどうすればよろしいで
しょうか？？（c1.txtはわたしの音声データです）

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

#define PI 3.14159265358979323846

/* sin table　*/
static void make_sintbl(n, sintbl)
int n;
float *sintbl;
{
int i, n2, n4, n8;
double c, s, dc, ds, t;
n2 = n / 2; n4 = n / 4; n8 = n / 8;
t = sin(PI / n);
dc = 2 * t * t; ds = sqrt(dc * (2 - dc));
t = 2 * dc;
c = sintbl[n4] = 1; s = sintbl[0] = 0;
for (i = 1; i < n8; i++) {
c -= dc; dc += t * c;
s += ds; ds -= t * s;
sintbl[i] = s; sintbl[n4 - i] = c;
}
if (n8 != 0) sintbl[n8] = sqrt(0.5);
for (i = 0; i < n4; i++)
sintbl[n2 - i] = sintbl[i];
for (i = 0; i < (n2 + n4); i++)
sintbl[i + n2] = - sintbl[i];
}

/* Bit Reversal */
static void make_bitrev(n, bitrev)
int n;
int *bitrev;
{
int i, j, k, n2;
n2 = n / 2; i = j = 0;
for ( ; ; ) {
bitrev[i] = j;
if (++i >= n) break;
k = n2;
while (k <= j) { j -= k; k /= 2; }
j += k;
}
}

/* FFT main routine */
int fft(n, x, y)
int n;
float *x;
float *y;
{
static int last_n = 0;
static int *bitrev = NULL;
static float *sintbl = NULL;
int i, j, k, ik, h, d, k2, n4, inverse;
float t, s, c, dx, dy;
/* preparation */
if (n < 0) {
n = -n; inverse = 1;
} else inverse = 0;
n4 = n / 4;
if (n != last_n || n == 0) {
last_n = n;
if (sintbl != NULL) free(sintbl);
if (bitrev != NULL) free(bitrev);
if (n == 0) return 0;
sintbl = malloc((n + n4) * sizeof(float));
bitrev = malloc(n * sizeof(int));
if (sintbl == NULL || bitrev == NULL) {
fprintf(stderr, Insufficient Memory\n);
return 1;
}
make_sintbl(n, sintbl);
make_bitrev(n, bitrev);
}
for (i = 0; i < n; i++) {
j = bitrev[i];
if (i < j) {
t = x[i]; x[i] = x[j]; x[j] = t;
t = y[i]; y[i] = y[j]; y[j] = t;
}
}
for (k = 1; k < n; k = k2) {
h = 0; k2 = k + k; d = n / k2;
for (j = 0; j < k; j++) {
c = sintbl[h + n4];
if (inverse) s = - sintbl[h];
else s = sintbl[h];
for (i = j; i < n; i += k2) {
ik = i + k;
dx = s * y[ik] + c * x[ik];
dy = c * y[ik] - s * x[ik];
x[ik] = x[i] - dx; x[i] += dx;
y[ik] = y[i] - dy; y[i] += dy;
}
h += d;
}
}
if (! inverse)
for (i = 0; i < n; i++) {
x[i] /= n; y[i] /= n;
}
return 0;
}

/ Main Program /

#define N 256

int main(argc, argv)
int argc;
char *argv[];
{
FILE *fp;
int i;
static float x1[N], y1[N], x2[N], y2[N], x3[N], y3[N];
if ((fp = fopen(c1.txt, r)) ==NULL){
printf (File Open Error \%s \ file.\n, c1.txt);
exit(1);
}
for (i = 0; i < N; i++) {
fscanf(fp, %f, &x1[i]);
x2[i] = x1[i] ;
y1[i] = y2[i] = 0;
}
if (fft(N, x2, y2)) return EXIT_FAILURE;
for (i = 0; i < N; i++) {
x3[i] = x2[i]; y3[i] = y2[i];
}
if (fft(-N, x3, y3)) return EXIT_FAILURE;
printf( Original data Fourier Transformed Inverse Transformed\n);
for (i = 0; i < N; i++)
printf(%4d | %6.3f %6.3f | %6.3f %6.3f | %6.3f %6.3f\n,
i, x1[i], y1[i], x2[i], y2[i], x3[i], y3[i]);
return EXIT_SUCCESS;
}