The gmp_prob_prime() is a built-in function in PHP which is used to check how much is the possibility of given GMP number(GNU Multiple Precision : For large numbers) to be prime or not.

This function uses Miller-Rabin primality test to check if the given GMP number is prime or not.

**Syntax:**

gmp_prob_prime($num)

**Parameters:** The function accepts a GMP number *$num* as mandatory parameter as shown in the above syntax. This parameter can be a GMP object in PHP version 5.6 and later, or we are also allowed to pass numeric string such that it is possible to convert this string in number.

**Return Value:** This function returns value in the range 0-2, **0** if the number is definitely not prime, **1** if the number may be prime else **2** if the number is surely prime.

Examples:

Input : gmp_prob_prime("8") Output : 0 Input : gmp_prob_prime("11111111111111") Output : 1 Input: gmp_prob_prime("127") Output: 2

Below programs illustrate the gmp_prob_prime() function in PHP:

**Program 1:** Program to find the prime probability of GMP number when numeric strings as GMP numbers are passed as arguments.

`<?php ` `// PHP program to find the prime probability of ` `// GMP numbers passed as arguments ` ` ` `// strings as GMP numbers ` `$num` `= ` `"17"` `; ` ` ` `// calculate the possibility ` `// of GMP number to be prime ` `$prob` `= gmp_prob_prime(` `$num` `); ` ` ` `echo` `$prob` `; ` `?> ` |

Output:

2

**Program 2:** Program to find the prime probability of GMP number when GMP numbers are passed as arguments.

`<?php ` `// PHP program to find the prime probability of ` `// GMP numbers passed as arguments ` ` ` `// creating GMP numbers using gmp_init() ` `$num` `= gmp_init(8); ` ` ` `// calculate the possibility of ` `// GMP number to be prime ` `$prob` `= gmp_prob_prime(` `$num` `); ` ` ` `echo` `$prob` `; ` `?> ` |

Output:

0

**Program 3:** Program to find the prime probability of GMP number when GMP numbers are passed as arguments.

`<?php ` `// PHP program to find the prime probability of ` `// GMP numbers passed as arguments ` ` ` `// creating GMP numbers using gmp_init() ` `$num` `= gmp_init(1111111111111111111); ` ` ` `// calculate the possibility of ` `// GMP number to be prime ` `$prob` `= gmp_prob_prime(` `$num` `); ` ` ` `echo` `$prob` `; ` `?> ` |

Output:

1

**Reference:**

php.net/manual/en/function.gmp-prob-prime.php

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