CheckDigits::MXX_002 - compute check digits for CAS

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

ALGORITHM
       1.  Beginning right with the second digit all digits are weighted ascending starting with 1.

       2.  The sum of those products is computed.

       3.  The checksum is the last digit of the sum from step 2 (modulo 10).

   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.

       CheckDigits::MXX_002 - compute check digits for CAS

       perl,               CheckDigits,                www.pruefziffernberechnung.de,                www.cas.orghttp://www.cas.org/expertise/cascontent/registry/checkdig.html

perl v5.36.0                                       2022-10-13               Algorithm::CheckDigits::MXX_002(3pm)

         use Algorithm::CheckDigits;

         $cas = CheckDigits('cas');

         if ($cas->is_valid('1333-74-0')) {
               # do something
         }

         $cn = $cas->complete('1333-74-');
         # $cn = '1333-74-0'

         $cd = $cas->checkdigit('1333-74-0');
         # $cd = '0'

         $bn = $cas->basenumber('1333-74-0');
         # $bn = '1333-74-'

       Aaron W. West pointed me to a fault in the computing of the check digit.

       HERMIER   Christophe   made   me   aware  that  CAS  is  now  assigning  10-digit  CAS  Registry  Numbers
       (http://www.cas.org/newsevents/10digitrn.html)