NAME

       CheckDigits::MXX_002 - compute check digits for CAS

SYNOPSIS

         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-'

DESCRIPTION

   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.

AUTHOR

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

THANKS

       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)

SEE ALSO

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