FA-60934 / Bond day-count conventions / Member archive

Act/Act ISDA year fraction: a reversed interval is silently swapped · case 04

Callers passing dates in the wrong order get a positive fraction instead of an error value.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Inputs start and end [y,m,d]. If end < start return "end before start". Split the interval at each 1 January; each piece contributes its actual days divided by 366 if the piece lies in a Gregorian leap year, else 365. Sum exactly and return the float rounded to 9 decimals.

Why this case matters

Bond accrual and pricing systems depend on exact day-count arithmetic; a single-day error changes settlement cash.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression reversed interval handling 1	`0.002739726`	`"end before start"`	Failed

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