merge Sort in php

<?php

function merge(array $arr1,array $arr2){
    $result=[];
    $i=0;
    $j=0;
    while ($i<count($arr1)&&$j<count($arr2)){
        if ($arr2[$j]>$arr1[$i]){
            $result[]=$arr1[$i];
            $i++;
        }else{
            $result[]=$arr2[$j];
            $j++;
        }
    }
    while ($i<count($arr1)){
        $result[]=$arr1[$i];
        $i++;
    }
    while ($j<count($arr2)){
        $result[]=$arr2[$j];
        $j++;
    }

    return $result;

}





function mergeSort(array $arr){
    if (count($arr)<=1)return $arr;
    $mid=floor(count($arr)/2);
    $left=mergeSort(array_slice($arr,0,$mid));
    $right=mergeSort(array_slice($arr,$mid));

    return merge($left,$right);


}