> +/* 15-point FFT exptab */
> +for (i = 0; i < 19; i++) {
> +if (i < 15) {
> +double theta = 2 * M_PI * i / 15;
> +s->exptab[i].re = cos(theta);
> +s->exptab[i].im = sin(theta);
> +} else { /* Wrap around to simplify fft[1]5 */
> +
First off, many thanks.
> +const int inv_1 = l_ptwo << ((4 - b_ptwo) & 3);
> +const int inv_2 = 0xeeef & ((1U << b_ptwo) - 1);
It would be nice to add a comment here that the expression for inv_1
is (2^b_ptwo)^-1 mod 15 and inv_2 is 15^-1 mod 2^b_ptwo. (A general
PFA FFT would need to
