FA-16945 / Floating-point arithmetic / Member archive

Decimal fused multiply-add applies the wrong addend sign · case 05

Decimal fused multiply-add applies the wrong addend sign.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Decimal fused multiply-add rounds a*b+c once in a fresh precision-limited half-even context. Inputs are decimal strings; return final decimal string and Inexact flag.

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
cancellation	`["11.2", true]`	`["-0.0012", false]`	Failed

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