gmp_prob_prime()

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

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$repsvary 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,$ais definitely not prime. If it returns 1, then$ais "probably" prime. If it returns 2, then$ais surely prime.

范例

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

<?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