gmp_gcd

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

gmp_gcd — Calculate GCD

Description

GMP gmp_gcd ( GMP $a , GMP $b )

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

Parameters

a: Either a GMP number resource in PHP 5.5 and earlier, a GMP object in PHP 5.6 and later, or a numeric string provided that it is possible to convert the latter to a number.
b: Either a GMP number resource in PHP 5.5 and earlier, a GMP object in PHP 5.6 and later, or a numeric string provided that it is possible to convert the latter to a number.

Return Values

A positive GMP number that divides into both a and b.

Examples

Example #1 gmp_gcd() example


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

The above example will output:

User Contributed Notes

Ludwig Heymbeeck

13 years ago


The following function is more accurate:

function GCD($num1, $num2) {
/* finds the greatest common factor between two numbers */
   while ($num2 != 0){
     $t = $num1 % $num2;
     $num1 = $num2;
     $num2 = $t;
   }
   return $num1;
}

bigkm1 at gmail dot com

9 years ago


here is an elegant recursive solution
<?php    

function gcd($a,$b) {
    return ($a % $b) ? gcd($b,$a % $b) : $b;
}

?>

sean__remove__ at eternalrise_r_emove__ dot com

7 years ago


Here's my solution for getting the GCD of several numbers.

<?php

/*
 * function gcd()
 * 
 * returns greatest common divisor
 * between two numbers
 * tested against gmp_gcd()
 */
function gcd($a, $b)
{
    if ($a == 0 || $b == 0)
        return abs( max(abs($a), abs($b)) );
        
    $r = $a % $b;
    return ($r != 0) ?
        gcd($b, $r) :
        abs($b);
}

/*
 * function gcd_array()
 * 
 * gets greatest common divisor among
 * an array of numbers
 */
function gcd_array($array, $a = 0)
{
    $b = array_pop($array);
    return ($b === null) ?
        (int)$a :
        gcd_array($array, gcd($a, $b));
}

?>

limas at kultur-online dot at

8 years ago


The previous function returns just 1 under php 5.2.4  but the following seems to work (m>0,n>0):

function gcd($m,$n)
{
    $_m=$m;$r=1;
    if($m<$n){$t=$m;$m=$n;$n=$t;}    
    while($r)
    {
        $r=(floor($m/$n)*$n)-$m;      
        $_n=$n;$n=$r;$m=$_m;
    }     
    return abs($_n);
}

scr02001 at student dot mdh dot se

12 years ago


If you do not consier a or b as possible negative numbers, a GCD funktion may return a negative GCD, wich is NOT a greatest common divisor, therefore a funktion like this may be better. This considers the simplyfying of (-3)-(-6) where gcd on -3 and -6 would result in 3, not -3 as with the other function. (-3)-(-6) is (-1)-(-2) NOT (1)-(2)

function eGCD($a,$b){
  if($a < 0)         $a=0-$a;
  if($b < 0 )        $b=0-$b;
  if($a == 0 || $b == 0)    return 1;
  if($a == $b)              return a; 
  
do{
  $rest=(int) $a % $b;  $a=$b; $b=$rest;
  }while($rest >0);
return $a;
}

x-empt-php dot net at ispep dot cx

13 years ago


No need to compile gmp functions in just for the GCD function...  use this one instead:

function GCD($num1, $num2) {
 /* finds the greatest common factor between two numbers */
    if ($num1 < $num2) {
        $t = $num1;
        $num1 = $num2;
        $num2 = $t;
    }
    while ($t = ($num1 % $num2) != 0) {
        $num1 = $num2;
        $num2 = $t;
    }
    return $num2;
}