FFT functions

[Paul Underwood]

> A generic interface for saving transformed operands might not be
> straightforward to design.  E.g., how should one handle operands of
> different sizes?
> 

To be more precise, the programmer could use say 20 rounds of generic
mpz_mul and mpz_mod before and after 1000's in the main loop of:

mpz_FFT_forward(pa, a, n);
mpz_FFT_forward(pb, b, n);
...
then calls to for example:
mpz_FFT_point_mul(pab, pa, pb);
mpz_FFT_point_mul(pa2, pa, pa);
mpz_FFT_reverse(ab, pab, n);
mpz_FFT_reverse(a2, pa2, n);

Best Wishes

Paul