gistfile1

function validateCreditCard($cardnumber, $cardname) {

  if ($cardname[0]) {
    // accept masked cc numbers
    return true;
  }

    $ccErrorNo = 0;
    $ccErrors = array ();
    $ccErrors[0] = "Unknown card type.";
    $ccErrors[1] = "No card number provided.";
    $ccErrors[2] = "Credit card number is in invalid format.";
    $ccErrors[3] = "Credit card number is invalid.";
    $ccErrors[4] = "Credit card number has an inappropriate number of digits.";

    // Array to hold the permitted card characteristics
    $cards = array();
    
    // Define the cards we support. You may add addtional card types.
    //  Name:      As in the selection box of the form - must be same as user's
    //  Length:    List of possible valid lengths of the card number for the card
    //  prefixes:  List of possible prefixes for the card
    //  checkdigit Boolean to say whether there is a check digit
    $cards[0] = array("name" => "Visa","length" => "13,16","prefixes" => "4","checkdigit" => true);
    $cards[1] = array("name" => "MasterCard","length" => "16","prefixes" => "51,52,53,54,55","checkdigit" => true);
    $cards[2] = array("name" => "DinersClub","length" => "14,16","prefixes" => "300,301,302,303,304,305,36,38,55","checkdigit" => true);
    $cards[3] = array("name" => "CarteBlanche","length" => "14","prefixes" => "300,301,302,303,304,305,36,38","checkdigit" => true);
    $cards[4] = array("name" => "AmEx","length" => "15","prefixes" => "34,37","checkdigit" => true);
    $cards[5] = array("name" => "Discover","length" => "16","prefixes" => "6011,650","checkdigit" => true);
    $cards[6] = array("name" => "JCB","length" => "15,16","prefixes" => "3,1800,2131","checkdigit" => true);
    $cards[7] = array("name" => "enRoute","length" => "15","prefixes" => "2014,2149","checkdigit" => true);
    $cards[8] = array("name" => "Solo","length" => "16,18,19","prefixes" => "6334, 6767","checkdigit" => true);
    $cards[9] = array("name" => "Switch","length" => "16,18,19","prefixes" => "4903,4905,4911,4936,564182,633110,6333,6759","checkdigit" => true);
    $cards[10] = array("name" => "Maestro", "length" => "16,18","prefixes" => "5020,6","checkdigit" => true);
    $cards[11] = array("name" => "VisaElectron","length" => "16","prefixes" => "417500,4917,4913","checkdigit" => true);
    // Establish card type
    $cardType = -1;
    for ($i=0; $i<count($cards); $i++) {
        // See if it is this card (ignoring the case of the string)
        if (strtolower($cardname.toLowerCase) == strtolower($cards[i]["name"])) {
            $cardType = $i;
            break;
        }
    }
    // If card type not found, report an error
    if ($cardType == -1) {
        $ccErrorNo = 0;
        return false; 
    }
    // Ensure that the user has provided a credit card number
    if (strlen($cardnumber) == 0)  {
        $ccErrorNo = 1;
        return false; 
    }
    // Now remove any spaces from the credit card number
    $cardnumber = preg_replace("/\s/g", "",$cardnumber);
    // Check that the number is numeric
    $cardNo = $cardnumber;
    $cardexp = "/^[0-9]{13,19}$/";
    if(!preg_match('/^[0-9]{13,19}$/', $cardNo)) {
        $ccErrorNo = 2;
        return false;
    }
    // Now check the modulus 10 check digit - if required
    if ($cards[$cardType]["checkdigit"]) {
        $checksum = 0;                                  // running checksum total
        $mychar = "";                                   // next char to process
        $j = 1;                                         // takes value of 1 or 2
        // Process each digit one by one starting at the right
        $calc;
        for ($i = strlen($cardNo) - 1; $i >= 0; $i--) {
          // Extract the next digit and multiply by 1 or 2 on alternative digits.
          $calc = int(substr($cardNo,$i,1)) * j;
          // If the result is in two digits add 1 to the checksum total
          if ($calc > 9) {
            $checksum = $checksum + 1;
            $calc = $calc - 10;
          }
          // Add the units element to the checksum total
          $checksum = $checksum + $calc;
          // Switch the value of j
          if ($j==1) {$j = 2;} else {$j = 1;}
        } 
        // All done - if checksum is divisible by 10, it is a valid modulus 10.
        // If not, report an error.
        if ($checksum % 10 != 0)  {
            $ccErrorNo = 3;
            return false; 
        }
    }  
    // The following are the card-specific checks we undertake.
    $LengthValid = false;
    $PrefixValid = false; 
    $undefined; 
    // We use these for holding the valid lengths and prefixes of a card type
    $prefix = array ();
    $lengths = array ();
    // Load an array with the valid prefixes for this card
    $prefix = split(",",$cards[$cardType]["prefixes"]);
    // Now see if any of them match what we have in the card number
    for ($i=0; $i<count($prefix); $i++) {
        $exp = "/^".$prefix[$i]."/";
        if (preg_match($exp,$cardNo)) $PrefixValid = true;
    }
    // If it isn't a valid prefix there's no point at looking at the length
    if (!$PrefixValid) {
        $ccErrorNo = 3;
        return false; 
    }
    // See if the length is valid for this card
    $lengths = split(",",$cards[$cardType]["length"]);
    for ($j=0; j<count(lengths); $j++) {
        if (strlen($cardNo) == $lengths[$j]) $LengthValid = true;
    }
    // See if all is OK by seeing if the length was valid. We only check the 
    // length if all else was hunky dory.
    if (!$LengthValid) {
        $ccErrorNo = 4;
        return false; 
    };
    // The credit card is in the required format.
    return true;
}