PHP信用卡卡号验证函数

/** ????* 验证银行卡号是否是信用卡 ????* @param $cardnumber ????* @return bool ????*/ ???function validateCard ($cardnumber){ ???????$cardnumber = preg_replace ("/\D|\s/","", $cardnumber); ???????$cardlength = strlen($cardnumber);if($cardlength !=0){ ???????????$parity = $cardlength %2; ???????????$sum =0; ???????????for($i=0; $i<$cardlength; $i++){ ???????????????$digit = $cardnumber[$i]; ???????????????if($i %2== $parity) $digit = $digit *2; ???????????????if($digit >9) $digit = $digit -9; ???????????????$sum = $sum + $digit; ???????????} ???????????$valid =($sum %10==0); ???????????return $valid; ???????} ???????return false; ???}