Cleanup TensorPrimitives

[lilinus]

• Delete unused code behind #if !NET directives but the files are only compiled for NETCoreApp.
• Delete IsNan/IsPositive/IsNegative helpers and just use the methods on vector classes directly.

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR modernizes TensorPrimitives’ vector paths by removing #if !NET fallback implementations and switching call sites to use the Vector128/256/512 APIs directly (e.g., Vector*.IsNaN, Vector*.IsPositive/IsNegative, Vector*.Min/Max).

Changes:

• Replaced internal/helper predicates (e.g., IsNaN, IsPositive, IsNegative) with direct Vector128/256/512 calls.
• Removed #if !NET fallback implementations for Exp, Log, and Log2 operators.
• Simplified vector Min/Max operators to expression-bodied calls to Vector*.Min/Max.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.Sign.cs	Uses Vector*.IsNaN directly for NaN detection in Sign.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.Round.cs	Removes #if !NET boundary constants previously used for fallback rounding logic.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.Min.cs	Drops #if !NET float/double special-casing; always uses Vector*.Min.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.Max.cs	Drops #if !NET float/double special-casing; always uses Vector*.Max and removes helper predicates.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.Log2.cs	Removes #if !NET polynomial/vector fallback implementations for Log2.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.Log.cs	Removes #if !NET polynomial/vector fallback implementations for Log.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.Exp.cs	Removes #if !NET polynomial/vector fallback implementations for Exp.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IsRealNumber.cs	Switches to direct Vector*.IsNaN for vectorized real-number testing.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IsPositive.cs	Switches to direct Vector*.IsPositive in vectorized paths.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IsNegative.cs	Switches to direct Vector*.IsNegative in vectorized paths.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IsNaN.cs	Switches to direct Vector*.IsNaN in vectorized paths.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IndexOfMinMagnitude.cs	Replaces helper sign checks with Vector*.IsNegative/IsPositive.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IndexOfMin.cs	Replaces helper sign checks with Vector*.IsNegative/IsPositive.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IndexOfMaxMagnitude.cs	Replaces helper sign checks with Vector*.IsNegative/IsPositive.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.IndexOfMax.cs	Replaces helper sign checks with Vector*.IsNegative/IsPositive.
src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/Common/TensorPrimitives.IIndexOfMinMaxOperator.cs	Replaces NaN detection helper with Vector*.IsNaN during vectorized scans.