int Fft::_FFT(double b[], int n)
{
double fn;
int i, in, nn, n2pow, n4pow;
if((n2pow = fastpurelog2(n)) <= 0) return 0;
fn = (double)n;
n4pow = n2pow / 2;
/* radix 2 iteration required; do it now */
if (n2pow % 2)
{
nn = 2;
in = n / nn;
FR2TR(in, b, b + in );
}
else nn = 1;
/* perform radix 4 iterations */
for(i = 1; i <= n4pow; i++)
{
nn *= 4;
in = n / nn;
FR4TR(in, nn, b, b + in, b + 2 * in, b + 3 * in);
}
/* perform inplace reordering */
FORD1(n2pow, b);
FORD2(n2pow, b);
return 1;
}
/*
** FAST(b,n)
** This routine replaces the real float vector b
** of length n with its finite discrete fourier transform.
** DC term is returned in b[0];
** n/2th harmonic real part in b[1].
** jth harmonic is returned as complex number stored as
** b[2*j] + i b[2*j + 1]
** (i.e., remaining coefficients are as a DPCOMPLEX vector).
**
*/
int FAST(real *b, int n) {
real fn;
int i, in, nn, n2pow, n4pow, nthpo;
n2pow = fastlog2(n);
if(n2pow <= 0) return 0;
nthpo = n;
fn = nthpo;
n4pow = n2pow / 2;
/* radix 2 iteration required; do it now */
if(n2pow % 2) {
nn = 2;
in = n / nn;
FR2TR(in, b, b + in);
}
else nn = 1;
/* perform radix 4 iterations */
for(i = 1; i <= n4pow; i++) {
nn *= 4;
in = n / nn;
FR4TR(in, nn, b, b + in, b + 2 * in, b + 3 * in);
}
/* perform inplace reordering */
FORD1(n2pow, b);
FORD2(n2pow, b);
/* take conjugates */
for(i = 3; i < n; i += 2) b[i] = -b[i];
return 1;
}
