CheckDigits::MXX_006 - compute check digits with Verhoeff scheme

use Algorithm::CheckDigits;
$verhoeff = CheckDigits('verhoeff');
if ($verhoeff->is_valid('14567894')) {
# do something
}
$cn = $verhoeff->complete('1456789');
# $cn = '14567894'
$cd = $verhoeff->checkdigit('14567894');
# $cd = '4'
$bn = $verhoeff->basenumber('14567894');
# $bn = '1456789'

- 1.
- Right to left all digits are permutated according to a
permutation table.

- 2.
- The permutated digits are combined using a dieeder table.
The first with the second, the result with the third, this result with the
fourth and so on.

- 3.
- The result of the last combination in the dieeder table is
in such a way combined that the result is 0 (zero). The number used for
this combination is the checksum.

For details look at the source.

- 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.

- 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.

Mathias Weidner, <mathias@weidner.in-bad-schmiedeberg.de>

Jonathan Peters wrote Algorithm::Verhoeff from which I took the routine to
compute the checkdigits.

perl, CheckDigits, <http://www.cs.utsa.edu/~wagner/laws/verhoeff.html>,
<http://www.cs.nmsu.edu/~cssem/Dickcheckdoc.pdf>