 CheckDigits::MXX_003(3) compute check digits for DEM

## SYNOPSIS

use Algorithm::CheckDigits;
\$dem = CheckDigits('dem');
if (\$dem->is_valid('GD0645027K1')) {
# do something
}
\$cn = \$dem->complete('GD0645027K');
# \$cn = 'GD0645027K1'
\$cd = \$dem->checkdigit('GD0645027K1');
# \$cd = '1'
\$bn = \$dem->basenumber('GD0645027K1');
# \$bn = 'GD0645027K'

## ALGORITHM

The algorithm is a variation of the Verhoeff scheme.
0
All letters are changed to numbers.
1
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 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]>