[FX.php List] [OFF] Luhn validation for Credit Card?

[Joel Shapiro]

Hi all

I've inherited a project that validates a basic credit card number  
within FMP using the Luhn algorithm

("The Luhn algorithm or Luhn formula, also known as the "modulus 10"  
or "mod 10" algorithm, is a simple checksum formula used to validate  
a variety of identification numbers, such as credit card numbers..."
http://en.wikipedia.org/wiki/Luhn_algorithm )

I'd rather check this in the PHP before submission to FMP.

Googling brings up many PHP code options, but I wanted to check if  
anyone here has one that they've used and like.

(Note, in this project the client manually processes all credit card  
orders after they come into FMP.  They just want to weed out  
definitely-fake cc #s)

TIA,
-Joel