Getting the number of weeks in a year

function nbWeekInAYear ($year) {
        $nbWeek = date('W',mktime(0, 0, 0, 12, 31, $year));
        if ($nbWeek==1) {
            $nbWeek = 52;
        }
        return $nbWeek;
}

echo nbWeekInAYear(2009)."\n"; //53 
echo nbWeekInAYear(2010)."\n"; //52
echo nbWeekInAYear(2011)."\n"; //52
echo nbWeekInAYear(2012)."\n"; //52
echo nbWeekInAYear(2013)."\n"; //52
echo nbWeekInAYear(2014)."\n"; //52
echo nbWeekInAYear(2015)."\n"; //53
echo nbWeekInAYear(2016)."\n"; //52