Tpetra_Details_IntRowPtrHelper.hpp

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#ifndef TPETRA_INTROWPTR_HELPER_HPP
#define TPETRA_INTROWPTR_HELPER_HPP

#include "Tpetra_CrsMatrix_fwd.hpp"
#include "Kokkos_Core.hpp"
#include "KokkosSparse_spmv_handle.hpp"

namespace Tpetra {
namespace Details {

template <typename LocalMatrix,
          typename IntLocalMatrix = KokkosSparse::CrsMatrix<typename LocalMatrix::value_type,
                                                            typename LocalMatrix::ordinal_type,
                                                            typename LocalMatrix::device_type,
                                                            void, int>>
struct IntRowPtrHelper {
  static_assert(is_crs_matrix_v<LocalMatrix> == is_crs_matrix_v<IntLocalMatrix>, "Expected both to be CrsMatrix or BlockCrsMatrix");

  using Rowptrs    = typename LocalMatrix::row_map_type;
  using IntRowptrs = typename IntLocalMatrix::row_map_type;

  IntRowPtrHelper(size_t nnz, const typename LocalMatrix::row_map_type& rowptrs)
    : nnz_(nnz) {
    if (shouldUseIntRowptrs())
      fillRowptrsInt(rowptrs);
    // otherwise, leave rowptrs_int empty
  }

  bool shouldUseIntRowptrs() const {
    // Use int-valued rowptrs if:
    // - number of entries doesn't overflow int
    // - LocalMatrix's rowptrs is not already int-typed
    return nnz_ <= size_t(INT_MAX) && !std::is_same_v<int, typename Rowptrs::non_const_value_type>;
  }

  void fillRowptrsInt(const Rowptrs& rowptrs) {
    // Populate rowptrs_int as a deep copy of rowptrs, converted to int.
    // This needs to be in its own public function because KOKKOS_LAMBDA cannot be used inside constructor or protected/private
    typename IntRowptrs::non_const_type rowptrs_temp(
        Kokkos::view_alloc(Kokkos::WithoutInitializing, "rowptrs_int"), rowptrs.extent(0));
    Kokkos::parallel_for(
        Kokkos::RangePolicy<typename LocalMatrix::execution_space>(0, rowptrs.extent(0)),
        KOKKOS_LAMBDA(int i) {
          rowptrs_temp(i) = int(rowptrs(i));
        });
    rowptrs_int_ = rowptrs_temp;
  }

  IntLocalMatrix getIntRowptrMatrix(const LocalMatrix& A) {
    if constexpr (KokkosSparse::is_crs_matrix_v<LocalMatrix>) {
      return IntLocalMatrix("", A.numRows(), A.numCols(), A.nnz(),
                            A.values, rowptrs_int_, A.graph.entries);
    } else {
      return IntLocalMatrix("", A.numRows(), A.numCols(), A.nnz(),
                            A.values, rowptrs_int_, A.graph.entries, A.blockDim());
    }
  }

  size_t nnz_;
  IntRowptrs rowptrs_int_;
};
}  // namespace Details
}  // namespace Tpetra

#endif  // TPETRA_INTROWPTR_HELPER_HPP