Hello Daniel!
We don't yet have any transform-only interface in GMP, but this will
probably change at some point.
The current FFT code uses coefficient rings mod 2^m+1, as per the
Schönhage-Strassen algorithm. In this algorithm, m = O(sqrt(n)) where n
= O(log(a) + log(b)) for multiplication of a
[This is a slightly revised version of a question I raised in
direct email. Sending to list per moderator suggestion. Possibly
I should have known to do that to begin with, but there was a
nagging suspicion that the question might be off base.]
This is in regard to operations that arise with asym