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# gmp_prob_prime

(PHP 4 >= 4.0.4, PHP 5)

gmp_prob_prime -- Check if number is "probably prime"

## Description

int gmp_prob_prime ( resource a [, int reps] )

If this function returns 0, `a` is definitely not prime. If it returns 1, then `a` is "probably" prime. If it returns 2, then `a` is surely prime. Reasonable values of `reps` vary from 5 to 10 (default being 10); a higher value lowers the probability for a non-prime to pass as a "probable" prime.

The function uses Miller-Rabin's probabilistic test.

例 1. gmp_prob_prime() example

`<?php // definitely not a prime echo gmp_prob_prime("6") . "\n"; // probably a prime echo gmp_prob_prime("1111111111111111111") . "\n"; // definitely a prime echo gmp_prob_prime("11") . "\n"; ?>`

The printout of the above program will be:

    0
    1
    2

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