Merge sort in PHP

gistfile1.php

<?php

function mergesort(&$array)
{
    _mergesort($array, 0, count($array));
}

function _mergesort(&$array, $left, $right)
{
    if ($right - $left <= 1) return;
    $mid = intval($left + ($right - $left) / 2);
    _mergesort($array, $left, $mid);
    _mergesort($array, $mid, $right);
    merge($array, $left, $mid, $right);
}

function merge(&$array, $left, $mid, $right)
{
    $l_index = $left;
    $r_index = $mid;
    $result = array();

    while ($l_index < $mid && $r_index < $right) {
        if ($array[$l_index] <= $array[$r_index]) {
            $result[] = $array[$l_index];
            $l_index++;
        } else {
            $result[] = $array[$r_index];
            $r_index++;
        }
    }
    while ($l_index < $mid) {
        $result[] = $array[$l_index];
        $l_index++;
    }
    while ($r_index < $right) {
        $result[] = $array[$r_index];
        $r_index++;
    }
    arrayCopy($result, $array, $left, $right);
}

function arrayCopy($resource, &$array, $start, $end)
{
    $res_index = 0;
    for ($i = $start; $i < $end; $i++) {
        $array[$i] = $resource[$res_index];
        $res_index++;
    }
}

$ar = array(3,1,5,11,12,3,9);
mergesort($ar);
var_dump($ar);
/*
array(7) {
  [0]=>
  int(1)
  [1]=>
  int(3)
  [2]=>
  int(3)
  [3]=>
  int(5)
  [4]=>
  int(9)
  [5]=>
  int(11)
  [6]=>
  int(12)
}
*/