are there any functions for computing a square root of a modulo p (prime)?

[Zimmermann Paul]

> *There's no API functions to calculate quadratic residues directly but you
> do have mpz_legendre() so all the tools are there to calculate it even for
> p = 1 mod 8. It's not deterministic though.*

indeed, see http://en.wikipedia.org/wiki/Tonelli%E2%80%93Shanks_algorithm.
The Tonelli–Shanks algorithm is so useful in many applications, that it
would make sense to have it implemented in GMP.

Paul