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//  This code is based on 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.

#ifndef vtkm_worklet_contourtree_degree_delta_h
#define vtkm_worklet_contourtree_degree_delta_h

#include <vtkm/worklet/WorkletMapField.h>
#include <vtkm/exec/ExecutionWholeArray.h>

namespace vtkm {
namespace worklet {
namespace contourtree {

// Worklet for doing regular to candidate
class DegreeDelta : public vtkm::worklet::WorkletMapField
{
public:
  typedef void ControlSignature(FieldIn<IdType> sortID,               // (input) index into sorted vertices [1..N]
                                WholeArrayIn<IdType> sortVector,      // (input) sorted vector of vertices
                                WholeArrayOut<IdType> candidate);     // (output) candidate
  typedef void ExecutionSignature(_1, _2, _3);
  typedef _1   InputDomain;

  vtkm::Id nCandidates;

  // Constructor
  VTKM_EXEC_CONT
  DegreeDelta(vtkm::Id NCandidates) : nCandidates(NCandidates) {}

  template <typename InFieldPortalType, typename OutFieldPortalType>
  VTKM_EXEC
  void operator()(const vtkm::Id& sortID,
                  const InFieldPortalType& sortVector,
                  const OutFieldPortalType& candidate) const
  {
    vtkm::Id iCandidate = sortVector.Get(sortID);
    // last element needs to be subtracted from vector size
    if (sortID == nCandidates-1)
    { // final element
      candidate.Set(iCandidate, (nCandidates - candidate.Get(iCandidate)));
    } // final element
    // otherwise, if the next one is different
    else
    { // not the last element
      vtkm::Id nextCandidate = sortVector.Get(sortID+1);
      if (iCandidate != nextCandidate)
      { // no match
        candidate.Set(iCandidate, (sortID+1 - candidate.Get(iCandidate)));
      } // no match                   
    } // not the last element
  }
}; // DegreeDelta

}
}
}

#endif
