[oak perl] Re: Customizing a Barcode Checkdigit Subroutine

[Belden Lyman]

David B. Peterson wrote:
> 
> There is an interesting property of numbers that you can use for this 
> calculation.
> 
> If you add the individual digits of a number and subtract 9 from it as 
> many times as necessary, you will eventually get the sum of the two 
> numbers.

For any base N counting system where N > 9, N - 1 has similar
properties. Mathemagics are nifty :)

> 
> Here is a little routine I wrote a hell of a long time ago for this 
> purpose.
> 
> sub LUHN10 {
>   my ($a, @cc, $sum);
>   my ($cc = @_[0]);
>   $cc =~ tr/0-9//cd;
>   @cc = split('', $cc);
>   while (@cc) {
>     $sum += pop(@cc);
>     $a = pop(@cc) * 2;
>     $a -= 9 if $a > 9;
>     $sum += $a;
>   }
>   return (!($sum % 10));
> }
> 
> used as such:
> 
> LUHN10('visa: 4444444444445555');
> LUHN10('4444 4444 4444 5555');
> 
> It doesn't care about any non digit chars.
> 

Two thoughts:

1. my ( $cc = @_[0] ); doesn't compile.
    btw, you mean $_[0], or shift(@_), but not @_[0].

2. sort() uses magical variables $a and $b, so it's a good
    idea to stay away from them.


> <rant>
> And as such, I'm always disgusted by commerce sites that require me to 
> leave the spaces out of my credit card number.  It shouldn't matter one 
> iota to the computer, but it sure makes it easier for me to see if I've 
> made a typo when I can put spaces in there.
> </rant>
> 

I agree. Rant at Jennifer, she's writing an e-commerce site right now ;)

Belden


> Have fun.
> 
> -Dave