Find whether two numbers are mutually prime (coprime)

Use the euclidean method to find out whether two numbers are prime numbers (prime numbers)

$a=200;
$b=13;
//Euclidean division method
if($b>$a){
 $x=$a;$a=$b;$ b=$x;
}
while(1){
 //echo "a=".$a." b=".$b;echo "n";
 if($b==1){echo " Reciprocally prime";break;}
 if($b==0){echo "Not reciprocally prime";break;}
 if($a-$b > $b){
 $a=$a-$b ;
 }else{
 $a=$a-$b;
 $x=$a;$a=$b;$b=$x;
 }
}
?>