Credit card identification

gistfile1.txt

function CreditCardCompany($ccNum)
{
    /*
     * mastercard: Must have a prefix of 51 to 55, and must be 16 digits in length.
     * Visa: Must have a prefix of 4, and must be either 13 or 16 digits in length.
     * American Express: Must have a prefix of 34 or 37, and must be 15 digits in length.
     * Diners Club: Must have a prefix of 300 to 305, 36, or 38, and must be 14 digits in length.
     * Discover: Must have a prefix of 6011, and must be 16 digits in length.
     * JCB: Must have a prefix of 3, 1800, or 2131, and must be either 15 or 16 digits in length.
     */

    if (ereg("^5[1-5][0-9]{14}$", $ccNum))
        return "Mastercard";

    if (ereg("^4[0-9]{12}([0-9]{3})?$", $ccNum))
        return "Visa";

    if (ereg("^3[47][0-9]{13}$", $ccNum))
        return "American Express";

    if (ereg("^6011[0-9]{12}$", $ccNum))
        return "Discover";
    return 'Credit';
}