FA-72414 / Check-digit algorithms / Member archive

Damm processes digits right to left · case 04

Check digits only match for palindromic payloads.

Member previewVariant 4 · 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 ["7689245619132", "generate"]	`0`	`9`	Failed

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