Binary search in PHP example

<?php
function bin_search($arr, $searchKey) {
    $left = 0;
    $right = count($arr);

    while($left < $right) {
        $middle = ($right + $left) / 2;
        if ($arr[$middle] == $searchKey) {
            $res = $middle;
            break;
        } elseif ($arr[$middle] > $searchKey) {
            $right = $middle;
        } else {
            $left = $middle + 1;
        }
    }
    return $res;
}
$exArr = array(1, 1, 2, 2, 3, 9, 11, 16);
$result = bin_search($exArr, 3);
print $result.PHP_EOL;