text: //============================================================================
  //  Copyright (c) Kitware, Inc.
  //  All rights reserved.
  //  See LICENSE.txt for details.
  //
  //  This software is distributed WITHOUT ANY WARRANTY; without even
  //  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
  //  PURPOSE.  See the above copyright notice for more information.
  //============================================================================
  // Copyright (c) 2018, The Regents of the University of California, through
  // Lawrence Berkeley National Laboratory (subject to receipt of any required approvals
  // from the U.S. Dept. of Energy).  All rights reserved.
  //
  // Redistribution and use in source and binary forms, with or without modification,
  // are permitted provided that the following conditions are met:
  //
  // (1) Redistributions of source code must retain the above copyright notice, this
  //     list of conditions and the following disclaimer.
  //
  // (2) Redistributions in binary form must reproduce the above copyright notice,
  //     this list of conditions and the following disclaimer in the documentation
  //     and/or other materials provided with the distribution.
  //
  // (3) Neither the name of the University of California, Lawrence Berkeley National
  //     Laboratory, U.S. Dept. of Energy nor the names of its contributors may be
  //     used to endorse or promote products derived from this software without
  //     specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
  // ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  // WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  // IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
  // INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  // BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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  // OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  // OF THE POSSIBILITY OF SUCH DAMAGE.
  //
  //=============================================================================
  //
  //  This code is an extension of the algorithm presented in the paper:
  //  Parallel Peak Pruning for Scalable SMP Contour Tree Computation.
  //  Hamish Carr, Gunther Weber, Christopher Sewell, and James Ahrens.
  //  Proceedings of the IEEE Symposium on Large Data Analysis and Visualization
  //  (LDAV), October 2016, Baltimore, Maryland.
  //
  //  The PPP2 algorithm and software were jointly developed by
  //  Hamish Carr (University of Leeds), Gunther H. Weber (LBNL), and
  //  Oliver Ruebel (LBNL)
  //==============================================================================
  
  #ifndef vtk_m_worklet_contourtree_distributed_bract_maker_boundary_tree_node_comparator_h
  #define vtk_m_worklet_contourtree_distributed_bract_maker_boundary_tree_node_comparator_h
  
  #include <vtkm/cont/ArrayHandle.h>
  #include <vtkm/cont/ArrayHandleMultiplexer.h>
  #include <vtkm/cont/ExecutionObjectBase.h>
  #include <vtkm/worklet/contourtree_augmented/Types.h>
  
  
  namespace vtkm
  {
  namespace worklet
  {
  namespace contourtree_distributed
  {
  namespace bract_maker
  {
  
  
  /// device implementation of the comparator used for sorting hyperarcs
  class BoundaryTreeNodeComparatorImpl
  {
  public:
    using IdArrayPortalType = vtkm::cont::ArrayHandle<vtkm::Id>::ReadPortalType;
    // The ContourTreeMesh uses a smart ArrayHandleIndex instead of a regular IdArrayType array.
    // That is why we use a ArrayHandleMultiplexer here.
    using SortIndexPortalType =
      vtkm::cont::ArrayHandleMultiplexer<vtkm::cont::ArrayHandle<vtkm::Id>,
                                         vtkm::cont::ArrayHandleIndex>::ReadPortalType;
  
    // constructor - takes vectors as parameters
    VTKM_CONT
    BoundaryTreeNodeComparatorImpl(const IdArrayPortalType& regularIdPortal,
                                   const SortIndexPortalType& meshSortIndexPortal)
      : RegularIdPortal(regularIdPortal)
      , MeshSortIndexPortal(meshSortIndexPortal)
    { // constructor
    } // constructor
  
    // () operator - gets called to do comparison
    VTKM_EXEC
    bool operator()(const vtkm::Id& i, const vtkm::Id& j) const
    { // operator()
      // retrieve the sort order
      vtkm::Id sortIndexI = MeshSortIndexPortal.Get(RegularIdPortal.Get(i));
      vtkm::Id sortIndexJ = MeshSortIndexPortal.Get(RegularIdPortal.Get(j));
  
      // now test on that
      if (sortIndexI < sortIndexJ)
      {
        return true;
      }
      else if (sortIndexJ < sortIndexI)
      {
        return false;
      }
  
      // fallback out of paranoia
      return false;
  
    } // operator()
  
  private:
    IdArrayPortalType RegularIdPortal;
    SortIndexPortalType MeshSortIndexPortal;
  }; // BoundaryTreeNodeComparatorImpl
  
  /// comparator used to compare hyperarcs for sort
  class BoundaryTreeNodeComparator : public vtkm::cont::ExecutionObjectBase
  {
  public:
    // constructor - takes vectors as parameters
    VTKM_CONT
    BoundaryTreeNodeComparator(
      const vtkm::worklet::contourtree_augmented::IdArrayType& regularId,
      const vtkm::cont::ArrayHandleMultiplexer<vtkm::cont::ArrayHandle<vtkm::Id>,
                                               vtkm::cont::ArrayHandleIndex>& meshSortIndex)
      : RegularId(regularId)
      , MeshSortIndex(meshSortIndex)
    { // constructor
    } // constructor
  
    VTKM_CONT BoundaryTreeNodeComparatorImpl PrepareForExecution(vtkm::cont::DeviceAdapterId device,
                                                                 vtkm::cont::Token& token) const
    {
      return BoundaryTreeNodeComparatorImpl(this->RegularId.PrepareForInput(device, token),
                                            this->MeshSortIndex.PrepareForInput(device, token));
    }
  
  private:
    vtkm::worklet::contourtree_augmented::IdArrayType RegularId;
    /// The ContourTreeMesh uses a smart ArrayHandleIndex instead of a regular IdArrayType array that is why we use a ArrayHandleMultiplexer here
    vtkm::cont::ArrayHandleMultiplexer<vtkm::cont::ArrayHandle<vtkm::Id>,
                                       vtkm::cont::ArrayHandleIndex>
      MeshSortIndex;
  }; // BoundaryTreeNodeComparator
  
  } // namespace bract_maker
  } // namespace contourtree_distributed
  } // namespace worklet
  } // namespace vtkm
  
  #endif
  