FA-17024 / Floating-point arithmetic / Member archive

Log divided difference uses log1p even when the normalized decrement rounds to minus one · case 04

Log divided difference uses log1p even when the normalized decrement rounds to minus one.

Member previewVariant 4 · 3 implementations · 10 checks per implementation

Case contract

Evaluate (log(b)-log(a))/(b-a) for positive finite endpoints with continuous limit 1/a. Close ratios use log1p; fixtures have finite outputs. Finite results are rendered to eleven significant decimal digits; modeled domain violations and arithmetic errors are explicit strings.

Why this case matters

An offline floating representation model isolates a reproducible arithmetic fault.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
far reverse	`"arithmetic-error"`	`"1.3815510558e-297"`	Failed

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