PHP验证信用卡卡号函数

 1 /**
 2      * 验证银行卡号是否是信用卡
 3      * @param $cardnumber
 4      * @return bool
 5      */
 6     function validateCard ($cardnumber){
 7         $cardnumber = preg_replace ("/\D|\s/","", $cardnumber);
 8         $cardlength = strlen($cardnumber);if($cardlength !=0){
 9             $parity = $cardlength %2;
10             $sum =0;
11             for($i=0; $i<$cardlength; $i++){
12                 $digit = $cardnumber[$i];
13                 if($i %2== $parity) $digit = $digit *2;
14                 if($digit >9) $digit = $digit -9;
15                 $sum = $sum + $digit;
16             }
17             $valid =($sum %10==0);
18             return $valid;
19         }
20         return false;
21     }