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//  this software.
//============================================================================
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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.

//=======================================================================================
//
// COMMENTS:
//
// Any vector needed by the functor for lookup purposes will be passed as a parameter to
// the constructor and saved, with the actual function call being the operator ()
//
// Vectors marked I/O are intrinsically risky unless there is an algorithmic guarantee
// that the read/writes are completely independent - which for our case actually occurs
// The I/O vectors should therefore be justified in comments both here & in caller
//
//=======================================================================================

#ifndef vtkm_worklet_contourtree_saddle_ascent_transferrer_h
#define vtkm_worklet_contourtree_saddle_ascent_transferrer_h

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

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Worklet for setting initial chain maximum value
class SaddleAscentTransferrer : public vtkm::worklet::WorkletMapField
{
public:
  typedef void ControlSignature(
    FieldIn<IdType> vertexID,          // (input) active vertex
    FieldIn<IdType> newOutdegree,      // (input) updated updegree
    FieldIn<IdType> newFirstEdge,      // (input) updated first edge of vertex
    WholeArrayIn<IdType> activeEdges,  // (input) active edges
    WholeArrayIn<IdType> firstEdge,    // (input) first edges
    WholeArrayOut<IdType> edgeSorter); // (output) edge sorter
  typedef void ExecutionSignature(_1, _2, _3, _4, _5, _6);
  typedef _1 InputDomain;

  // Constructor
  VTKM_EXEC_CONT
  SaddleAscentTransferrer() {}

  template <typename InFieldPortalType, typename OutFieldPortalType>
  VTKM_EXEC void operator()(const vtkm::Id& vertexID,
                            const vtkm::Id& newOutdegree,
                            const vtkm::Id& newFirstEdge,
                            const InFieldPortalType& activeEdges,
                            const InFieldPortalType& firstEdge,
                            const OutFieldPortalType& edgeSorter) const
  {
    // loop through the edges from the vertex
    for (vtkm::Id edge = 0; edge < newOutdegree; edge++)
    {
      // compute which index in the new sorting array
      vtkm::Id edgeSorterIndex = newFirstEdge + edge;
      // now retrieve the old edge
      vtkm::Id edgeID = activeEdges.Get(firstEdge.Get(vertexID) + edge);
      // adding them to the edge sort array
      edgeSorter.Set(edgeSorterIndex, edgeID);
    }
  }

}; // SaddleAscentTransferrer
}
}
}

#endif
