gmp_prob_prime

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

gmp_prob_prime — Check if number is "probably prime"

说明

gmp_prob_prime ( GMP $a [, int $reps = 10 ] ) : int

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

参数

a

The number being checked as a prime.

可以是一个 GMP 数据 resouce，或一个可以转换为数值的字符串。

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.

可以是一个 GMP 数据 resouce，或一个可以转换为数值的字符串。

返回值

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.

范例

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";
?>

以上例程会输出：

0
1
2

User Contributed Notes

florin dot ciuica at yahoo dot com 26-Sep-2014 10:00


<?php

    $max = 2147483647;

    

    $primesFound = 0;

    $probablePrimes = 0;



    for ($x = 1; $x <= $max; $x++) {

        $primeStatus = gmp_prob_prime($x);

        if ($primeStatus == 1) {

            $probablePrimes++;

        } else if ($primeStatus == 2) {

            $primesFound++;

        }

    }

    echo "Total primes found: " . $primesFound . " between 1 and " . $max . ". Probable primes in this interval: " . $probablePrimes;

?>



Based on that the following results were obtained:



1 - 100000      - certain primes found: 9592,     probable: 0

1 - 1000000     - certain primes found: 78498,    probable: 0

1 - 10000000    - certain primes found: 78498,    probable: 586081

1 - 100000000   - certain primes found: 78498,    probable: 5682957

1 - 1000000000  - certain primes found: 78498,    probable: 50769036

1 - 2147483647  - certain primes found: 78498,    probable: 105019067