FA-72543 / Check-digit algorithms / Member archive

CUSIP doubles the first character of each pair · case 03

Most CUSIPs are rejected.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

CUSIP check: nine ASCII characters, the ninth a digit. Payload values: digits face value, A-Z 10-35, * 36, @ 37, # 38 (anything else "malformed"). Every second payload character (1-based even position) is doubled, and the decimal digits of each value are summed. Return [(10 - sum % 10) % 10, whether it equals the ninth digit].

Why this case matters

Clearing and custody systems validate North American security identifiers.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression ["462107IA0"]	`[4, false]`	`[3, false]`	Failed

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