FA-72410 / Check-digit algorithms / Member archive

Damm looks up the digit row instead of the interim row · case 05

Most generated check digits disagree with the Damm reference.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Damm quasigroup scheme with the standard order-10 table. Spaces are ignored; the remaining text must be nonempty ASCII digits or the result is None. Digits are processed left to right with interim = T[interim][digit] from 0; "generate" returns the final interim value, "validate" returns whether it is 0.

Why this case matters

Damm checks are used on order and parcel references where transpositions must be detected.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression ["5727", "validate"]	`true`	`false`	Failed

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