function getCdr($cdr = 0)
{
    $temp = '';
    $c = floor($cdr/26);
    if ($c == 0 || $cdr == 25) {
        $temp .= chr($cdr+65);
    } else {
        $y = $cdr%26;
        $temp .= chr($c+64) . chr($y+65);
    }
    return $temp;
}

仅支持到 zz 但已经满足需求