Расчет ISRC-кода

/*///////////////////////////////////////////////////////////////

 ISRC, PHP, 2010-12-10
 
 ISRC = CC-XXX-YY-NNNNN
    CC = RU
    XXX = COMPANY
    YY = YEAR
    NNNNN = number
 
 Artix, master@7masterov.ru, icq:53666599, skype:artixmaster
 
 * Error in code? Nothing is perfect!
 * Free source for free Linux, use it for free!
 * Please, do not remove this comment!

///////////////////////////////////////////////////////////////*/


function genISRC($country='RU',$company='STK',$year=0,$number=0) {
    static $n=1;
    if ($number>99999) $number=0;
    if ($year==0) $year = date('y');
    if ($number!=0) $n=$number;
    $code=$country.$company.$year.sprintf("%05d",$n++);
    return $code;
}

function checkISRC($code) {
    if (strlen($code)==12)
        if (preg_match('/\d\d\d\d\d\d\d$/',$code))
            return true;
    return false;
}

$x = genISRC();
echo checkISRC($x)? "$x correct\n" : "$x incorrect!\n";