```{index} single: probab_prime; Math::GMP function ``` ```{index} single: Math::GMP::probab_prime; Perl function ``` # probab_prime Probabilistic primality test: return `0`, `1`, or `2`. ## Synopsis ```perl my $x = Math::GMP->new(7); my $v = $x->probab_prime(10); # 2 — definitely prime ``` ## What you get back - `0` — definitely composite. - `1` — probably prime (no witness found in `$reps` rounds). - `2` — definitely prime (small numbers, or `libgmp` proved it). `$reps` is the Miller-Rabin round count; higher values cost more but tighten the confidence on a `1` answer. A round count of `25` is a common default for cryptographic work.