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gmp_fact	gmp_gcdext

GMP Functions	Last updated: Mon, 26 Oct 2026

gmp_gcd

(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

gmp_gcd — Calculate GCD

Description

function gmp_gcd(GMP|int|string $num1, GMP|int|string $num2): GMP

Calculate greatest common divisor of num1 and num2. The result is always positive even if either of, or both, input operands are negative.

Parameters

num1: A GMP object, an int, or a string that can be interpreted as a number following the same logic as if the string was used in gmp_init() with automatic base detection (i.e. when base is equal to 0).
num2: A GMP object, an int, or a string that can be interpreted as a number following the same logic as if the string was used in gmp_init() with automatic base detection (i.e. when base is equal to 0).

Return Values

A positive GMP number that divides into both num1 and num2.

Examples

Example #1 gmp_gcd() example

<?php
$gcd = gmp_gcd("12", "21");
echo gmp_strval($gcd) . "\n";
?>

The above example will output:

See Also

gmp_lcm() - Calculate LCM

gmp_fact	gmp_gcdext

GMP Functions	Last updated: Mon, 26 Oct 2026