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gmp_gcd

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

gmp_gcdCalculate 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:

3

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User Contributed Notes 7 notes

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9
bigkm1 at gmail dot com
11 years ago
here is an elegant recursive solution
<?php   

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

?>
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5
Ludwig Heymbeeck
14 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;
}
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3
sean__remove__ at eternalrise_r_emove__ dot com
9 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));
}

?>
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0
delboy1978uk at gmail dot com
28 days ago
I wanted this functionality without having to install the extension.

So here's a script I wrote to find out the greatest common denominator:

<?php

// Our fraction, 3/12, could be written better
$numerator = 3;
$denominator = 12;

/**
* @param int $num
* @return array The common factors of $num
*/
function getFactors($num)
{
   
$factors = [];
   
// get factors of the numerator
   
for ($x = 1; $x <= $num; $x ++) {
        if (
$num % $x == 0) {
           
$factors[] = $x;
        }
    }
    return
$factors;
}

/**
* @param int $x
* @param int $y
*/
function getGreatestCommonDenominator($x, $y)
{
   
// first get the common denominators of both numerator and denominator
   
$factorsX = getFactors($x);
   
$factorsY = getFactors($y);
   
   
// common denominators will be in both arrays, so get the intersect
   
$commonDenominators = array_intersect($factorsX, $factorsY);
   
   
// greatest common denominator is the highest number (last in the array)
   
$gcd = array_pop($commonDenominators);
    return
$gcd;
}

// divide the numerator and denomiator by the gcd to get our refactored fraction
$gcd = getGreatestCommonDenominator($numerator, $denominator);
echo (
$numerator / $gcd) .'/'. ($denominator / $gcd); // we can use divide (/) because we know result is an int :-)

Which you can see running here https://3v4l.org/uTucY
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0
limas at kultur-online dot at
9 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);
}
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-1
scr02001 at student dot mdh dot se
14 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;
}
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-5
x-empt-php dot net at ispep dot cx
15 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;
}
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