Validate Danish CPR

validate-cpr.php

//  Validate CPR-nr.
function is_cpr_valid($cpr) {

    $cleaned = preg_replace("/[^0-9]/", "", $cpr);

    if (strlen($cleaned) != 10) {
        return FALSE;
    }

    $valid_dates = Array('010165', '010166', '010170', '010180', '010187', '010190');

    if (in_array(substr($cleaned, 0, 6), $valid_dates)) {
        return TRUE;
    }

    $cpr_arr = str_split($cleaned, 1);
    $mul_arr = str_split("4327654321", 1);

    $sum = 0;
    for ($i = 0; $i < count($cpr_arr); $i++) {
        $sum += $cpr_arr[$i] * $mul_arr[$i];
    }

    if ($sum % 11 == 0) {
        return TRUE;
    } else {
        return FALSE;
    }
}