NAME

       CheckDigits::M23_002 - compute check digits for VAT Registration Number (IE)

SYNOPSIS

         use Algorithm::CheckDigits;

         $dni = CheckDigits('ustid_ie');

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

         $cn = $dni->complete('8473625');
         # $cn = '8473625E'

         $cd = $dni->checkdigit('8473625E');
         # $cd = 'E'

         $bn = $dni->basenumber('8473625E');
         # $bn = '8473625'

DESCRIPTION

   ALGORITHM
       1.  Beginning right all digits are weighted with their position in the number (i.e. the
           number left from the check digit is multiplied with 2, the next with 3 and so on).

       2.  All products are added.

       3.  The check digit is the sum from step 2 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 consists solely of numbers and the last digit is a valid
           check digit according to the algorithm given above.

           Returns false otherwise,

       complete($number)
           The check digit for $number is computed and concatenated to the end of $number.

           Returns the complete number with check digit or '' if $number does not consist solely
           of digits and spaces.

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

           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, <mathias@weidner.in-bad-schmiedeberg.de>

SEE ALSO

       perl, CheckDigits, www.pruefziffernberechnung.de.