NAME

       CheckDigits::M16_001 - compute check digits for ISAN

SYNOPSIS

         use Algorithm::CheckDigits;

         $isan = CheckDigits('isan');

         if ($isan->is_valid('123A567B8912E01A')) {
               # do something
         }

         $cn = $isan->complete('123A567B8912E01');
         # $cn = '123A567B8912E01A'

         $cd = $isan->checkdigit('123A567B8912E01A');
         # $cd = '4'

         $bn = $isan->basenumber('123A567B8912E01A');
         # $bn = '123A567B8912E01'

DESCRIPTION

   ALGORITHM
       1.  "a(1) = 16"

           "b(i) = a(i) % 17 +d(i)", where d(i) is the decimal value of the hexdigit at position
           i.

           "c(i) = b(i) % 16"

           "a(i) = c(i-1) * 2", for i greater than 1

       2.  Beginning left for each i = 1..16, "a", "b", "c" are computed.

       3.  The check digit is the value for "d(16)" where "c(16)" equals 1.

       4.  The check digit is appended as hexadecimal value to the number.

   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.