- bool FFT(int dir,int m,double *x,double *y)
- {
- long nn,i,i1,j,k,i2,l,l1,l2;
- double c1,c2,tx,ty,t1,t2,u1,u2,z;
-
- /* Calculate the number of points */
- nn = 1<<m;
-
- /* Do the bit reversal */
- i2 = nn >> 1;
- j = 0;
- for (i=0;i<nn-1;i++) {
- if (i < j) {
- tx = x[i];
- ty = y[i];
- x[i] = x[j];
- y[i] = y[j];
- x[j] = tx;
- y[j] = ty;
- }
- k = i2;
- while (k <= j) {
- j -= k;
- k >>= 1;
- }
- j += k;
- }
-
- /* Compute the FFT */
- c1 = -1.0;
- c2 = 0.0;
- l2 = 1;
- for (l=0;l<m;l++) {
- l1 = l2;
- l2 <<= 1;
- u1 = 1.0;
- u2 = 0.0;
- for (j=0;j<l1;j++) {
- for (i=j;i<nn;i+=l2) {
- i1 = i + l1;
- t1 = u1 * x[i1] - u2 * y[i1];
- t2 = u1 * y[i1] + u2 * x[i1];
- x[i1] = x[i] - t1;
- y[i1] = y[i] - t2;
- x[i] += t1;
- y[i] += t2;
- }
- z = u1 * c1 - u2 * c2;
- u2 = u1 * c2 + u2 * c1;
- u1 = z;
- }
- c2 = sqrt((1.0 - c1) / 2.0);
- if (dir == 1)
- c2 = -c2;
- c1 = sqrt((1.0 + c1) / 2.0);
- }
-
- /* Scaling for forward transform */
- if (dir == 1) {
- for (i=0;i<nn;i++) {
- x[i] /= (double)nn;
- y[i] /= (double)nn;
- }
- }
-
- return true;
- }
bool FFT(int dir,int m,double *x,double *y)
{
long nn,i,i1,j,k,i2,l,l1,l2;
double c1,c2,tx,ty,t1,t2,u1,u2,z;
/* Calculate the number of points */
nn = 1<<m;
/* Do the bit reversal */
i2 = nn >> 1;
j = 0;
for (i=0;i<nn-1;i++) {
if (i < j) {
tx = x[i];
ty = y[i];
x[i] = x[j];
y[i] = y[j];
x[j] = tx;
y[j] = ty;
}
k = i2;
while (k <= j) {
j -= k;
k >>= 1;
}
j += k;
}
/* Compute the FFT */
c1 = -1.0;
c2 = 0.0;
l2 = 1;
for (l=0;l<m;l++) {
l1 = l2;
l2 <<= 1;
u1 = 1.0;
u2 = 0.0;
for (j=0;j<l1;j++) {
for (i=j;i<nn;i+=l2) {
i1 = i + l1;
t1 = u1 * x[i1] - u2 * y[i1];
t2 = u1 * y[i1] + u2 * x[i1];
x[i1] = x[i] - t1;
y[i1] = y[i] - t2;
x[i] += t1;
y[i] += t2;
}
z = u1 * c1 - u2 * c2;
u2 = u1 * c2 + u2 * c1;
u1 = z;
}
c2 = sqrt((1.0 - c1) / 2.0);
if (dir == 1)
c2 = -c2;
c1 = sqrt((1.0 + c1) / 2.0);
}
/* Scaling for forward transform */
if (dir == 1) {
for (i=0;i<nn;i++) {
x[i] /= (double)nn;
y[i] /= (double)nn;
}
}
return true;
}