[release/10.0] Non-zero result of Vector3.Cross with parallel vectors#119450
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artl93 merged 3 commits intorelease/10.0from Sep 8, 2025
Merged
[release/10.0] Non-zero result of Vector3.Cross with parallel vectors#119450artl93 merged 3 commits intorelease/10.0from
artl93 merged 3 commits intorelease/10.0from
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Co-authored-by: Tanner Gooding <tagoo@outlook.com>
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CC. @jeffhandley for initial bar check |
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This has my support for .NET 10 RC2. Functional fix for a regression introduced in .NET 9. If a customer reports being blocked by this in .NET 9 I would also support a reactive backport to .NET 9 servicing.
/cc @artl93
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Tagging subscribers to this area: @dotnet/area-system-numerics |
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Backport of #119438 to release/10.0
/cc @tannergooding @pedrobsaila
Customer Impact
Developers using
Vector3.Cross(x, x)(that is the cross-product of parallel vectors) to be zero and would get a non-zero result.Regression
This was regressed sometime in .NET 9 and wasn't caught due to it being non-LTS. The fix was introduced as part of an optimization to use
MultiplyAddEstimatewhich allows the use ofFusedMultiplyAddon hardware that supports it, similarly to other vector math libraries (such as DirectX Math). This instruction is more accurate but can also cause a non-zero result in some edge cases due to the additional precision and inherent rounding error.Testing
An explicit regression test was added.
Risk
Low risk. This simply changes out
MultiplyAddEstimate(a, b, c)for an explicit(a * b) + cinstead so that fusing can no longer occur.