Merge Sort in PHP

<?php

class MergeSort {
   
   public static function sort(&$arr) {
       $arrClone = $arr;
       MergeSort::_sort($arr, 0, count($arr) - 1, $arrClone);
   }

   public static function _sort(&$arr, $low, $high, $arrClone) {
       if($low < $high) {
           $mid = (int) (($low + $high) / 2);

           MergeSort::_sort($arr, $low, $mid, $arrClone);
           MergeSort::_sort($arr, $mid + 1, $high, $arrClone);

           MergeSort::merge($arr, $low, $mid, $high, $arrClone);
       }
   }

   public static function merge(&$arr, $low, $mid, $high, $arrClone) {
       $i = $low;
       $j = $mid + 1;

       for($k = $low; $k <= $high; $k++) {
           $arrClone[$k] = $arr[$k];
       }
       for($k = $low; $k <= $high; $k++) {
           if($i > $mid) {
               $arr[$k] = $arrClone[$j];
               $j++;
           }
           elseif($j > $high) {
               $arr[$k] = $arrClone[$i];
               $i++;
           }
           elseif($arrClone[$i] > $arrClone[$j]) {
               $arr[$k] = $arrClone[$j];
               $j++;
           }
           else {
               $arr[$k] = $arrClone[$i];
               $i++;
           }
       }
   }
}