* work if %$p$% is composite: you must factor the modulus, take
* a square root mod each factor, and recombine the results
* using the Chinese Remainder Theorem.
+ *
+ * We guarantee that the square root returned is the smallest
+ * one (i.e., the `positive' square root).
*/
extern mp *mp_modsqrt(mp */*d*/, mp */*a*/, mp */*p*/);