FA-60912 / Bond day-count conventions / Member archive

Act/Act ISDA year fraction: every calendar piece uses the start year basis · case 02

Spans crossing from a non-leap year into a leap year divide leap-year days by 365.

Member previewVariant 2 · 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 segment denominator year 1	`4.942465753`	`4.939726027`	Failed

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