gmp_prob_prime

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.

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 printout of the above program will be:

0
1
2
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