gmp_gcd

sean__remove__ at eternalrise_r_emove__ dot com (2008-11-10 19:50:01)

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));
}

?>

jim dot mayes at gmail dot com (2008-04-03 13:53:25)

Try...
function gcd($a, $b){
$b = ( $a == 0 )? 0 : $b;
return ( $a % $b )? gcd($b, abs($a - $b)) : $b;
}
always returns positive number even if one or both numbers are negative (as per the gmp_gcd function)
order agnostic, larger number can be $b or $a doesn't matter
also, other examples here were failing when one of the numbers was 0

limas at kultur-online dot at (2007-12-01 10:44:18)

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);
}

bigkm1 at gmail dot com (2006-08-25 21:33:03)

here is an elegant recursive solution
<?php    

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

?>

scr02001 at student dot mdh dot se (2003-08-16 06:58:39)

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;
}

Ludwig Heymbeeck (2003-01-12 10:33:08)

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;
}

x-empt-php dot net at ispep dot cx (2002-07-06 23:16:36)

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;
}