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lib/Algorithm/CheckDigits/M11_001.pm  view on Meta::CPAN

	my $number = shift;

	if ($number =~ /^[-0-9A-Za-z]+$/) {

		$number =~ s/-//g;
		my @digits = split(//,$number);
		my $sum    = 0;
		my $weight = 2;

		for (my $i = $#digits; $i >= 0; $i--) {

			$digits[$i] = 1 + ord(uc($digits[$i])) - ord('A')
				if ($digits[$i] =~ /[A-Z]/i);
			$sum += $weight * $digits[$i];
			++$weight;

		}
		$sum %= 11;
		return $cd->{$self->{type}}[11-$sum] if ($cd->{$self->{type}});
	}
	return -1;
} # _compute_checkdigit()

# Preloaded methods go here.

1;
__END__

=head1 NAME

CheckDigits::M11_001 - compute check digits for ISBN, ISSN, VAT RN
(PT), HKID (HK), Wagon number (BR), NHS (GB), VAT (SL)

=head1 SYNOPSIS

  use Algorithm::CheckDigits;

  $isbn = CheckDigits('isbn');

  if ($isbn->is_valid('3-88229-192-3')) {
	# do something
  }

  $cn = $isbn->complete('3-88229-192-');
  # $cn = '3-88229-192-3'

  $cd = $isbn->checkdigit('3-88229-192-3');
  # $cd = '3'

  $bn = $isbn->basenumber('3-88229-192-3');
  # $bn = '3-88229-192-'
  
=head1 DESCRIPTION

=head2 ALGORITHM

=over 4

=item 1

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).

=item 2

The sum of all products is computed.

=item 3

The sum of step 2 is taken modulo 11.

=item 4

The checkdigit is the difference of the sum from step 3 to eleven
under the following conditions:

=over 8

=item isbn,issn

If the difference is 10, the check digit is 'X'.

If the difference is 11, the check digit is 0.

=item ustid_pt

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

=item hkid

If the difference is 10, the check digit is 'A'.

If the difference is 11, the check digit is 0.

=item wagonnr_br

If the difference is 10, the check digit is 0.

If the difference is 11, the check digit is 1.

=item nhs_gb

If the difference is 10, the number would not be taken.

If the difference is 11, the check digit is 0.

=item vat_sl

This is a little bit unclear, don't trust on the method for this type.

=back

=back

=head2 METHODS

=over 4