Insertion Sort in PHP

<?php

class InsertionSort {
   public static function sort(&$arr) {
       // iterate over the array
       for($i = 0; $i < count($arr); $i++) {
           $tmp = $arr[$i];
           $j = $i - 1;
           while($j >= 0 && $arr[$j] > $tmp) {
               $arr[$j + 1] = $arr[$j];
               $j = $j - 1;
           }
           $arr[$j + 1] = $tmp;
       }
   }
}