barcode.xq

xquery version "3.0";
declare namespace mdc = "http://mdc";

declare function mdc:add-check-digit-to-partial-barcode ($partial-barcode as xs:string) as xs:string {
(: the next two variables compute the Codabar barcode sum for 14-digit library barcodes according to the Luhn algorithm:)
let $barcode-sum := 
                (: add up the even sequence :)
                sum(string-to-codepoints($partial-barcode)[position() mod 2 eq 0] ! xs:integer(codepoints-to-string(.)))
                +
                (: add up the odd sequence :)
                sum(string-to-codepoints($partial-barcode)[position() mod 2 eq 1] ! 
                  (if (xs:integer(codepoints-to-string(.)) >=  5) 
                  then xs:integer(codepoints-to-string(.)) * 2 - 9
                  else xs:integer(codepoints-to-string(.)) * 2))

let $check-digit := if ($barcode-sum mod 10 = 0) then 0 else 10 - $barcode-sum mod 10
return concat($partial-barcode, $check-digit)
};
(: check digit returned should be 6 :)
mdc:add-check-digit-to-partial-barcode('3900204393039')