NAME
CheckDigits::M11_001  compute check digits for ISBN, ISSN, VAT RN (PT), HKID (HK), Wagon number (BR), NHS (GB), VAT (SL)
SYNOPSIS
use Algorithm::CheckDigits;
$isbn = CheckDigits('isbn');
if ($isbn>is_valid('3882291923')) {
# do something
}
$cn = $isbn>complete('388229192');
# $cn = '3882291923'
$cd = $isbn>checkdigit('3882291923');
# $cd = '3'
$bn = $isbn>basenumber('3882291923');
# $bn = '388229192'
DESCRIPTION
ALGORITHM
The sequence of digits is processed right to left. Every digit is multiplied with their position in the sequence (i.e. the digit left to the check digit has the weight 2 then 3 etc.).
With a Hongkong ID (hkid) the leftmost char is replaced with its position in the alphabet and then multiplied with 8 (its weight).
The sum of all products is computed.
The sum of step 2 is taken modulo 11.
The checkdigit is the difference of the sum from step 3 to eleven under the following conditions:
 isbn,issn

If the difference is 10, the check digit is 'X'.
If the difference is 11, the check digit is 0.
 ustid_pt

If the difference is greater then 9, the check digit is '0'.
 hkid

If the difference is 10, the check digit is 'A'.
If the difference is 11, the check digit is 0.
 wagonnr_br

If the difference is 10, the check digit is 0.
If the difference is 11, the check digit is 1.
 nhs_gb

If the difference is 10, the number would not be taken.
If the difference is 11, the check digit is 0.
 vat_sl

This is a little bit unclear, don't trust on the method for this type.
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, <mamawe@cpan.org>
SEE ALSO
perl, CheckDigits, www.pruefziffernberechnung.de.