Improve precision of TP exponentiation functions. #99705
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Tagging subscribers to this area: @dotnet/area-system-numerics |
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Are there corresponding changes to be made to VectorMath in corelib? |
Not sure. Do these routines have precision issues as well? |
It's a copy of the same code, e.g. . The code being changed here for Exp for example only applies to .NET 8; on .NET 9 that code from Corelib ends up being used. |
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I was only running the .NET 9 tests when working on this, so clearly something's off here. |
| Vector128<double> a0 = MultiplyAddEstimateOperator<double>.Invoke(Vector128.Create(C12), r, Vector128.Create(C11)); | ||
| Vector128<double> a1 = MultiplyAddEstimateOperator<double>.Invoke(Vector128.Create(C10), r, Vector128.Create(C9)); | ||
| Vector128<double> a2 = MultiplyAddEstimateOperator<double>.Invoke(Vector128.Create(C8), r, Vector128.Create(C7)); | ||
| Vector128<double> a3 = MultiplyAddEstimateOperator<double>.Invoke(Vector128.Create(C6), r, Vector128.Create(C5)); | ||
| Vector128<double> a4 = MultiplyAddEstimateOperator<double>.Invoke(Vector128.Create(C4), r, Vector128.Create(C3)); | ||
| Vector128<double> a5 = MultiplyAddEstimateOperator<double>.Invoke(a0, r2, a1); | ||
| Vector128<double> a6 = MultiplyAddEstimateOperator<double>.Invoke(a2, r2, a3); | ||
| Vector128<double> a7 = MultiplyAddEstimateOperator<double>.Invoke(a4, r2, r + Vector128<double>.One); |
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nit: This many locals isn't really "good" for the JIT and can hinder some optimizations.
It can also make it a little bit harder to follow the intended computation ordering, which can itself limit other optimizations or reorderings the JIT would be allowed to do.
We could reduce the local count significantly if we broke it up like this, and then its also equivalent in codegen to as if there were no locals at all:
Vector128<double> t1 = MultiplyAddEstimate(
MultiplyAddEstimate(Vector128.Create(C12), r, Vector128.Create(C11)),
r2,
MultiplyAddEstimate(Vector128.Create(C10), r, Vector128.Create(C9))
);
Vector128<double> t2 = MultiplyAddEstimate(
MultiplyAddEstimate(Vector128.Create(C8), r, Vector128.Create(C7)),
r2,
MultiplyAddEstimate(Vector128.Create(C6), r, Vector128.Create(C5))
);
t1 = MultiplyAddEstimate(t1, r8, t2);
t2 = MultiplyAddEstimate(Vector128.Create(C4), r, Vector128.Create(C3));
t2 = MultiplyAddEstimate(t2, r2, r + Vector128<double>.One);
MultiplyAddEstimate(t1, r4, t2);
Updating the implementations to use FMA where applicable.
NB tests might require some calibration pending test results from platforms without FMA support.