# NAME

CheckDigits::M10_004 - compute check digits for 2aus5, EAN, ILN, ISBN13, NVE

# SYNOPSIS

``````  use Algorithm::CheckDigits;

\$ean = CheckDigits('ean');

if (\$ean->is_valid('7622200004607')) {
# do something
}

\$cn = \$ean->complete('762220000460');
# \$cn = '7622200004607'

\$cd = \$ean->checkdigit('7622200004607');
# \$cd = '7'

\$bn = \$ean->basenumber('7622200004607');
# \$bn = '762220000460'
``````

# DESCRIPTION

## ALGORITHM

1. Beginning right all numbers are weighted alternatively 1 and 3 (that is the check digit is weighted 1).

3. The sum of step 3 ist taken modulo 10.

4. The check digit is the difference between 10 and the number from step 3.

To validate the total of the digits of all numbers inclusive check digit taken modulo 10 must be 0.

## METHODS

is_valid(\$number)

Returns true only if `\$number` consists solely of digits, spaces and hyphen 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, spaces and hyphen.

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.

None by default.

# BUGS AND LIMITATIONS

When invoked as `CheckDigits('isbn13')` the module checks whether the first three digits (the country code) are 978 or 979, the current (as of 2006) EAN country codes for books. If at any time other EAN country codes for ISBN-13 will be specified and the then responsible maintainer ignores this in the code, please send a friendly email.

# AUTHOR

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