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Description:

damm 1.0

Damm algorithm decimal check digit
Note that check digits are NOT used for verification of data transfers between
computers – use a CRC or a hash for that purpose! Check digits are used to
check manual entry of a digit into a computer system.
A Damm check digit is a single check digit that can detect any
single-digit error as well as any adjacent-digit transpositions. The digit
computed in this module also detects some important phonetic errors (13<->30,
14<->40, … 19<–>90).
This makes the Damm check digit better than other, more well-known check digits
like the Luhn code (used in credit cards) and the ISBN base-11 check digit. It
is equal in detection strength to a Verhoeff check digit, but much simpler to
compute.
Furthermore, a hexadecimal Damm check digit was added. This single hexadecimal
check digit that detects every single-digit error as well as any adjacent-digit
transpositions. The digit computed in this module also detects some important
phonetic errors (13<->30, 14<->40, … 19<–>90). It also detects all
jump-transposition errors (abc -> cba), 93.5 % of all twin digit errors (aa ->
bb) and 93.5 % of all jump twin digit errors (aca -> bcb).
There are four functions in this module: encode, encode16, check and
check16. The first two, encode and encode16 are used to calculate the
check digit for a number that you have. Pass in a string with the number you
want encoded and get a string with the check digit back. The other two, check
and check16 are used to check that a number that was entered was entered
correctly. Pass in a string with a number including check digit and get back
True/False.

Damm algorithm
The Damm check digit is computed by starting with a check digit of zero and then
continually multiplying this check digit with the digits of a given number,
using the multiplication of a totally anti-symmetric quasigroup. The properties
and the selection of the group ensure the qualities of the check digit stated
above.
For further reference on how the algorithm works see
http://en.wikipedia.org/wiki/Damm_algorithm

License information
Copyright (C) 2013 Johannes Spielmann
This module, damm, is licensed under the terms of the GNU General Public Licenses as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
For a full description of the license, please see the file

LICENSE