 CheckDigits::M11_013(3) 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';

## 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.
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 hyphens and the two digits in the middle are valid check digits according to the algorithm given above.

Returns false otherwise,

complete(\$number)
The check digit for \$number is computed and inserted into the middle of \$number.

Returns the complete number with check digit or '' if \$number does not consist solely of digits, hyphens and spaces.

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, <[email protected]>