SYNOPSIS
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');
# $bn = '1456789'
DESCRIPTION
ALGORITHM
 1.
 Right to left all digits are permutated according to a permutation table.
 2.
 The permutated digits are combined using a die.der table. The first with the second, the result with the third, this result with the fourth and so on.
 3.
 The result of the last combination in the die.der table is in such a way combined that the result is 0 (zero). The number used for this combination is the checksum.
For details look at the source.
METHODS
 is_valid($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 $number does not consist solely of digits.
 basenumber($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.