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# NAME

CheckDigits::M11_013 - compute check digits for VAT Registration Number (GR)

# SYNOPSIS

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

\$ustid = CheckDigits('ustid_gr');

if (\$ustid->is_valid('123456783')) {
# do something
}

\$cn = \$ustid->complete('12345678');
# \$cn = '123456783'

\$cd = \$ustid->checkdigit('123456783');
# \$cd = '3'

\$bn = \$ustid->basenumber('123456783');
# \$bn = '12345678';
``````

# DESCRIPTION

## ALGORITHM

1. Beginning right with the digit before the checkdigit all digits are weighted with 2 ** position. I. e. the last digit is multiplied with 2, the next with 4, then 8 and so on.

2. The weighted digits are added.

3. The sum from step 2 is taken modulo 11.

4. If the sum from step 3 is greater than 9, the check sum is 0 else it is the sum itself.

## METHODS

is_valid(\$number)

Returns true only if `\$number` consists solely of numbers and the rightmost 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 appended to the end of `\$number`.

Returns the complete number with check digit or '' if `\$number` does not consist solely of digits.

basenumber(\$number)

Returns the basenumber of `\$number` if `\$number` has a valid check digit.

Return '' otherwise.

checkdigit(\$number)

Returns the check digits of `\$number` if `\$number` has valid check digits.

Return '' otherwise.

None by default.

# AUTHOR

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