PERF: Remove BSplineInterpolationWeightFunction Kernel, use FastEvaluate

Removed the dynamically allocated `m_Kernel` data member from
`BSplineInterpolationWeightFunction` and replaced the virtual function
call `m_Kernel->Evaluate(x)` by a faster static member function call, to
the newly added `BSplineKernelFunction::FastEvaluate` member function.

May significantly improve the performance of
`BSplineInterpolationWeightFunction`.

Modules/Core/Common/include/itkBSplineInterpolationWeightFunction.h

@@ -20,7 +20,6 @@
 
 #include "itkFunctionBase.h"
 #include "itkContinuousIndex.h"
-#include "itkBSplineKernelFunction.h"
 #include "itkArray.h"
 #include "itkArray2D.h"
 #include "itkMath.h"
@@ -122,12 +121,6 @@ class ITK_TEMPLATE_EXPORT BSplineInterpolationWeightFunction
 
   /** Table mapping linear offset to indices. */
   TableType m_OffsetToIndexTable;
-
-  /** Interpolation kernel type. */
-  using KernelType = BSplineKernelFunction<Self::SplineOrder>;
-
-  /** Interpolation kernel. */
-  typename KernelType::Pointer m_Kernel;
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkBSplineInterpolationWeightFunction.hxx

@@ -19,6 +19,7 @@
 #define itkBSplineInterpolationWeightFunction_hxx
 
 #include "itkBSplineInterpolationWeightFunction.h"
+#include "itkBSplineKernelFunction.h"
 #include "itkImage.h"
 #include "itkMatrix.h"
 #include "itkMath.h"
@@ -44,10 +45,6 @@ BSplineInterpolationWeightFunction<TCoordRep, VSpaceDimension, VSplineOrder>::BS
     }
     ++counter;
   }
-
-
-  // Initialize the interpolation kernel
-  m_Kernel = KernelType::New();
 }
 
 /**
@@ -104,7 +101,7 @@ BSplineInterpolationWeightFunction<TCoordRep, VSpaceDimension, VSplineOrder>::Ev
 
     for (k = 0; k <= SplineOrder; ++k)
     {
-      weights1D[j][k] = m_Kernel->Evaluate(x);
+      weights1D[j][k] = BSplineKernelFunction<SplineOrder>::FastEvaluate(x);
       x -= 1.0;
     }
   }