NAME

       CheckDigits::M23_002 - compute check digits for Tax Identification Number (IE)

SYNOPSIS

         use Algorithm::CheckDigits;

         $dni = CheckDigits('tin_ie');

         if ($dni->is_valid('8473625E')) {
               # do something
         }

         $cn = $dni->complete('1234567.W');
         # $cn = '1234567TW'

         $cd = $dni->checkdigit('1234577IA');
         # $cd = 'I'

         $bn = $dni->basenumber('1234577WW');
         # $bn = '1234577.W'

DESCRIPTION

   ALGORITHM
       The irish TIN (Tax Identification Number) or VAT Regstration Number consists of 7 digits,
       a letter in the range from 'A' - 'W' as checksum, and an optionally letter in the range
       from 'A' - 'I' or the letter 'W'.

       1.  In reverse order, each digit is multiplied by a weight started at 2.  (i.e. the number
           left from the check digit is multiplied with 2, the next with 3 and so on).

       2.  If there is an optional letter following the checksum letter (position 9), this letter
           is mapped to a numeric value based on the following mapping: "A" = 1, "B" = 2, ... "H"
           = 8, "I" = 9. "W" or absence of this letter means a value of 0. This numeric value is
           multiplied with 9.

       3.  All products from step 1 and 2 are added.

       4.  The check digit is the sum from step 3 modulo 23. This number is expressed as the
           corresponding letter from the alphabet where A-V correspond to 1-22 and W stands for
           check digit 0.

   METHODS
       is_valid($number)
           Returns true only if $number complies with the rules given above and there is a valid
           check digit at position eight.

           Returns false otherwise,

       complete($number)
           The check digit for $number is computed and inserted at position eight of $number.

           Returns the complete number with check digit or '' if $number does not consist solely
           of digits and an optional letter at position nine.

       basenumber($number)
           Returns the basenumber of $number if $number has a valid check digit. As a placeholder
           for the checksum a point ('.') is inserted at position eight when the checksum
           contains the optional letter at position nine.

           Return '' otherwise.

       checkdigit($number)
           Returns the checkdigit of $number if $number has a valid check digit.

           Return '' otherwise.

   EXPORT
       None by default.

AUTHOR

       Mathias Weidner, "<mamawe@cpan.org>"

SEE ALSO

       perl, CheckDigits, https://ec.europa.eu/taxation_customs/tin/