обрезка массива

function cutTheArray($array, $start, $length = null) {
    $count = count($array);
    if($start < 0) {
        $start = $count + $start;
    }

    if($length !== null) {
        if($length < 0) {
            $length = $count - $start + $length;
        }
        return array_slice($array, $start, $length);
    } else {
        return array_slice($array, $start);
    }
}

cutTheArray([1, 2, 3, 4, 5, 6], 2, 1); // [3]
cutTheArray([1, 2, 3, 4, 5, 6], 0, 3); // [1, 2, 3]
cutTheArray([1, 2, 3, 4, 5, 6], -2); // [5, 6]