++ed by:

2 non-PAUSE users.

Mathias Weidner

# NAME

CheckDigits::M10_003 - compute check digits for ISMN

# SYNOPSIS

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

\$ismn = CheckDigits('ismn');

if (\$ismn->is_valid('M-345-24680-5')) {
# do something
}

\$cn = \$ismn->complete('M-345-24680');
# \$cn = 'M-345-24680-5'

\$cd = \$ismn->checkdigit('M-345-24680-5');
# \$cd = '5'

\$bn = \$ismn->basenumber('M-345-24680-5');
# \$bn = 'M-345-24680'
``````

# DESCRIPTION

## ALGORITHM

1. The 'M' as the first number gets the value 3. Beginning left all numbers are weighted alternatively 3 and 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 taken 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.

None by default.

# AUTHOR

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