Cache Exp in SoftMax calculation (#111615)

* fix softmax

* Sum(destination)

Author: BarionLP

src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/TensorPrimitives.Single.cs

@@ -859,9 +859,9 @@ public static void SoftMax(ReadOnlySpan<float> x, Span<float> destination)
 
             ValidateInputOutputSpanNonOverlapping(x, destination);
 
-            float expSum = Aggregate<ExpOperator_Single, AddOperator_Single>(x);
-
-            InvokeSpanScalarIntoSpan<ExpOperator_Single, DivideOperator_Single>(x, expSum, destination);
+            InvokeSpanIntoSpan<ExpOperator_Single>(x, destination);
+            float expSum = Sum(destination);
+            InvokeSpanScalarIntoSpan<DivideOperator_Single>(destination, expSum, destination);
         }
 
         /// <summary>Computes the element-wise difference between single-precision floating-point numbers in the specified tensors.</summary>

src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorPrimitives.SoftMax.cs

@@ -36,9 +36,9 @@ public static void SoftMax<T>(ReadOnlySpan<T> x, Span<T> destination)
 
             ValidateInputOutputSpanNonOverlapping(x, destination);
 
-            T expSum = Aggregate<T, ExpOperator<T>, AddOperator<T>>(x);
-
-            InvokeSpanScalarIntoSpan<T, ExpOperator<T>, DivideOperator<T>>(x, expSum, destination);
+            InvokeSpanIntoSpan<T, ExpOperator<T>>(x, destination);
+            T expSum = Sum(destination);
+            InvokeSpanScalarIntoSpan<T, DivideOperator<T>>(destination, expSum, destination);
         }
     }
 }