Re: PL/pgSQL function to validate UPC and EAN barcodes

Miles Keaton presumably uttered the following on 06/25/05 01:44:
> I've made a PL/pgSQL function to validate UPC and EAN barcodes.
>
> It works correctly, but is a little ugly.
>
> Wondering if any PL/pgSQL experts can offer some suggestions.  (I'm
> new to PL/pgSQL.)
>
> Main questions:
> #1 - I wanted to add a "0" to the front of the barcode if it was only
> 12 characters long.  Seems that the incoming "barcode" variable was
> immutable, so I had to create a new variable ("b") to hold the
> possibly-new version.   Any more elegant way to do this?
>
> #2 - The big ugly : having to cast every digit in the substring into
> an integer so I could add them together.   Any shorter way to do this?
>
> For details on how it's validated, see "COMPUTING THE CHECKSUM DIGIT", here:
> http://www.barcodeisland.com/ean13.phtml
>
> Thanks!
>
>
> ------------
> CREATE OR REPLACE FUNCTION valid_barcode(barcode text) RETURNS boolean
> AS $function$
> DECLARE
>   b text;
>   odd int;
>   even int;
>   s int;
> BEGIN
>   IF LENGTH(barcode) < 12 OR LENGTH(barcode) > 13 THEN
>     return false;
>   END IF;
>   -- normalize UPC and EAN to both be 13 digits
>   IF LENGTH(barcode) = 12 THEN
>     b = '0' || barcode;
>   ELSE
>     b = barcode;
>   END IF;
>   -- sum of odd digits times 3, plus sum of even digits
>   even = CAST(SUBSTR(b, 1, 1) AS int) + CAST(SUBSTR(b, 3, 1) AS int) +
> CAST(SUBSTR(b, 5, 1) AS int) + CAST(SUBSTR(b, 7, 1) AS int) +
> CAST(SUBSTR(b, 9, 1) AS int) + CAST(SUBSTR(b, 11, 1) AS int);
>   odd = CAST(SUBSTR(b, 2, 1) AS int) + CAST(SUBSTR(b, 4, 1) AS int) +
> CAST(SUBSTR(b, 6, 1) AS int) + CAST(SUBSTR(b, 8, 1) AS int) +
> CAST(SUBSTR(b, 10, 1) AS int) + CAST(SUBSTR(b, 12, 1) AS int);
>   s = (3 * odd) + even;
>   -- remainder to nearest 10 should be same as last check digit
>   IF (CAST((CEIL(CAST(s AS float8) / 10) * 10) AS int) % s) =
> CAST(SUBSTR(b, 13, 1) AS int) THEN
>     return true;
>   ELSE
>     return false;
>   END IF;
> END;
> $function$ LANGUAGE plpgsql;
>

Perhaps it would be faster to accept the UPC code as a bigint in your
function then your initial tests would be by value (if barcode <
10,000,000,000,000,000 ... etc); you would only have to cast once in the
case of a short barcode (b = '0' || barcode)::bigint

Then you could create a loop, with a counter i starting at
1,000,000,000,000;
i := 1000000000000
WHILE i > 0 LOOP
    odd := odd + (b/i); b := b - ((b/i) *i); i = i/10;
    even := even + (b/i); b := b - ((b/i)*i); i = i/10;
END LOOP;
-- and so on

The math may be a bit off there, but the idea is to play with the number
as a number instead of a lot of casting. Just a thought.

Sven