CheckDigits::M10_003(3) 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'

## ALGORITHM

1.
The 'M' as the first number gets the value 3. Beginning left all numbers are weighted alternatively 3 and 1.
2.
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, <[email protected]>