LCC04Traversal.h

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#pragma once
 
#include "autopas/containers/cellTraversals/C08BasedTraversal.h"
#include "autopas/containers/linkedCells/traversals/LCC08CellHandler.h"
#include "autopas/containers/linkedCells/traversals/LCTraversalInterface.h"
#include "autopas/utils/ArrayUtils.h"
#include "autopas/utils/ThreeDimensionalMapping.h"
#include "autopas/utils/WrapOpenMP.h"
 
namespace autopas {
 
template <class ParticleCell, class PairwiseFunctor>
class LCC04Traversal : public C08BasedTraversal<ParticleCell, PairwiseFunctor>, public LCTraversalInterface {
 public:
  LCC04Traversal(const std::array<unsigned long, 3> &dims, PairwiseFunctor *pairwiseFunctor, double interactionLength,
                 const std::array<double, 3> &cellLength, DataLayoutOption dataLayout, bool useNewton3)
      : C08BasedTraversal<ParticleCell, PairwiseFunctor>(dims, pairwiseFunctor, interactionLength, cellLength,
                                                         dataLayout, useNewton3),
        _cellOffsets32Pack(computeOffsets32Pack()),
        _cellHandler(pairwiseFunctor, this->_cellsPerDimension, interactionLength, cellLength, this->_overlap,
                     dataLayout, useNewton3),
        _end(utils::ArrayMath::subScalar(utils::ArrayUtils::static_cast_copy_array<long>(this->_cellsPerDimension),
                                         1l)) {}
 
  void traverseParticles() override;
 
  [[nodiscard]] TraversalOption getTraversalType() const override { return TraversalOption::lc_c04; }
 
  [[nodiscard]] bool isApplicable() const override {
    // The cellsize cannot be smaller then the cutoff, if OpenMP is used.
    // Also see: https://github.com/AutoPas/AutoPas/issues/464
    const double minLength = *std::min_element(this->_cellLength.cbegin(), this->_cellLength.cend());
    const unsigned long minDim = *std::min_element(this->_cellsPerDimension.cbegin(), this->_cellsPerDimension.cend());
 
    return minLength >= this->_interactionLength and minDim > 3;
  }
 
  void setSortingThreshold(size_t sortingThreshold) override { _cellHandler.setSortingThreshold(sortingThreshold); }
 
 private:
  void traverseSingleColor(std::vector<ParticleCell> &cells, int color);
 
  void processBasePack32(std::vector<ParticleCell> &cells, const std::array<long, 3> &base3DIndex);
 
  constexpr auto computeOffsets32Pack() const;
 
  [[nodiscard]] constexpr long parity(long x, long y, long z) const { return (x + y + z + 24) % 8; }
 
  std::array<std::array<long, 3>, 32> _cellOffsets32Pack;
 
  LCC08CellHandler<ParticleCell, PairwiseFunctor> _cellHandler;
 
  std::array<long, 3> _end;
};
 
template <class ParticleCell, class PairwiseFunctor>
constexpr auto LCC04Traversal<ParticleCell, PairwiseFunctor>::computeOffsets32Pack() const {
  using std::make_pair;
  using utils::ThreeDimensionalMapping::threeToOneD;
 
  std::array<std::array<long, 3>, 32> cellOffsets32Pack = {};
 
  unsigned int i = 0;
  long z = 0l;
  cellOffsets32Pack[i++] = {1l, 1l, z};
  cellOffsets32Pack[i++] = {1l, 2l, z};
  cellOffsets32Pack[i++] = {2l, 1l, z};
  cellOffsets32Pack[i++] = {2l, 2l, z};
 
  // z = 1ul; z = 2ul
  for (z = 1l; z < 3l; ++z) {
    for (long y = 0l; y < 4l; y++) {
      for (long x = 0l; x < 4l; x++) {
        if ((x == 0l and y == 0l) or (x == 3l and y == 0l) or (x == 0l and y == 3l) or (x == 3l and y == 3l)) {
          continue;
        }
        cellOffsets32Pack[i++] = {x, y, z};
      }
    }
  }
 
  z = 3ul;
  cellOffsets32Pack[i++] = {1l, 1l, z};
  cellOffsets32Pack[i++] = {1l, 2l, z};
  cellOffsets32Pack[i++] = {2l, 1l, z};
  cellOffsets32Pack[i++] = {2l, 2l, z};
 
  if (i != 32) {
    utils::ExceptionHandler::exception("Internal error: Wrong number of offsets (expected: 32, actual: {})", i);
  }
 
  return cellOffsets32Pack;
}
 
template <class ParticleCell, class PairwiseFunctor>
void LCC04Traversal<ParticleCell, PairwiseFunctor>::processBasePack32(std::vector<ParticleCell> &cells,
                                                                      const std::array<long, 3> &base3DIndex) {
  using utils::ThreeDimensionalMapping::threeToOneD;
  std::array<long, 3> index{};
  const std::array<long, 3> signedDims = utils::ArrayUtils::static_cast_copy_array<long>(this->_cellsPerDimension);
 
  for (auto offset32Pack : _cellOffsets32Pack) {
    // compute 3D index
    bool isIn = true;
    for (int d = 0; d < 3; ++d) {
      index[d] = base3DIndex[d] + offset32Pack[d];
      isIn &= (index[d] >= 0l) and (index[d] < _end[d]);
    }
 
    if (isIn) {
      const unsigned long ulIndex = threeToOneD(index, signedDims);
      _cellHandler.processBaseCell(cells, ulIndex);
    }
  }
}
 
template <class ParticleCell, class PairwiseFunctor>
void LCC04Traversal<ParticleCell, PairwiseFunctor>::traverseParticles() {
  auto &cells = *(this->_cells);
  AUTOPAS_OPENMP(parallel) {
    for (int color = 0; color < 4; ++color) {
      traverseSingleColor(cells, color);
 
      if (color < 3) {
        AUTOPAS_OPENMP(barrier)
      }
    }
  }  // close parallel region
}
 
template <class ParticleCell, class PairwiseFunctor>
void LCC04Traversal<ParticleCell, PairwiseFunctor>::traverseSingleColor(std::vector<ParticleCell> &cells, int color) {
  // we need to traverse one body-centered cubic (BCC) grid, which consists of two cartesian grids
 
  // colors 0 and 2 form one cartesian grid
  // colors 1 and 3 form another cartesian grid, whose origin is shifted by (2,2,2)
 
  // determine a starting point of one of the grids
  std::array<long, 3> startOfThisColor{};
 
  switch (color % 2) {
    case 0:
      // colours 0 and 2
      startOfThisColor = {-2l, -2l, -2l};
      break;
    case 1:
      // colours 1 and 3
      startOfThisColor = {0l, 0l, 0l};
      break;
  }
 
  // calculate whether the calculated starting point is part of the color
  long correctParity = parity(startOfThisColor[0], startOfThisColor[1], startOfThisColor[2]);
  if (color >= 2) {
    correctParity += 4;
  }
 
  // to fix intel64 icpc compiler complaints about perfectly nested loop (tested with version 19.0.4.20190416).
  const long startX = startOfThisColor[0], endX = _end[0];
  const long startY = startOfThisColor[1], endY = _end[1];
  const long startZ = startOfThisColor[2], endZ = _end[2];
 
  // first cartesian grid
  // grids are interlinked: one grid fills the gaps in the other grid
  AUTOPAS_OPENMP(for schedule(dynamic, 1) collapse(3) nowait)
  for (long z = startZ; z < endZ; z += 4) {
    for (long y = startY; y < endY; y += 4) {
      for (long x = startX; x < endX; x += 4) {
        const long par = parity(x, y, z);
 
        if (par != correctParity) {
          continue;
        }
 
        const std::array<long, 3> base3DIndex = {x, y, z};
        processBasePack32(cells, base3DIndex);
      }
    }
  }
}
 
}  // namespace autopas