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 {
 8     $cardnumber = preg_replace ("/D|s/","", $cardnumber);
 9     $cardlength = strlen($cardnumber);
10     if($cardlength !=0){
11         $parity = $cardlength %2;
12         $sum =0;
13         for($i=0; $i<$cardlength; $i++){
14             $digit = $cardnumber[$i];
15             if($i %2== $parity) $digit = $digit *2;
16             if($digit >9) $digit = $digit -9;
17             $sum = $sum + $digit;
18         }
19         $valid =($sum %10==0);
20         return $valid;
21     }
22     return false;
23 }