PHP: Check if number is "probably prime"

Description

int gmp_prob_prime ( resource $a [, int $reps ] )

The function uses Miller-Rabin's probabilistic test to check if a number is a prime.

Parameters

a

The number being checked as a prime.

It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.

reps

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.

It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.

Return Values

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.

Examples

Example #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 above example will output:

0
1
2