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Luhn algorithm for validating credit cards

Posted in: algorithms, php | Save to del.icio.us | Twit This! 9 Jul 2008

The Luhn algorithm also known as the “modulus 10″ or “mod 10″ algorithm, is a checksum formula which can be used to validate credit card numbers. Developed in the 1950’s by IBM scientist Hans Peter Luhn and described in U.S. Patent 2,950,048. A PHP implementation is shown below.

 
function LuhnCheck($strDigits)
{
    $sum = 0;
    $alt = false;
    for($i = strlen($strDigits) - 1; $i >= 0; $i--) 
    {
        if($alt)
        {
           $temp = $strDigits[$i];
           $temp *= 2;
           $strDigits[$i] = ($temp > 9) ? $temp = $temp - 9 : $temp;
        }
        $sum += $strDigits[$i];
        $alt = !$alt;
    }
    return $sum % 10 == 0;
}

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1 Response

1

May 21st, 2009 at 2:36 am

Looks pretty well optimized too. Great post!
Will like to play with this function and read through it more slowly later on when I have some free time

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