Tpetra_Details_getEntryOnHost.hpp

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// @HEADER
// *****************************************************************************
//          Tpetra: Templated Linear Algebra Services Package
//
// Copyright 2008 NTESS and the Tpetra contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER

#ifndef TPETRA_DETAILS_GETENTRYONHOST_HPP
#define TPETRA_DETAILS_GETENTRYONHOST_HPP


#include "TpetraCore_config.h"
#include "Kokkos_Core.hpp"

namespace Tpetra {
namespace Details {

template <class ViewType,
          class IndexType>
typename ViewType::non_const_value_type
getEntryOnHost(const ViewType& x,
               const IndexType ind) {
  using execution_space = typename ViewType::execution_space;
  static_assert(ViewType::rank == 1, "x must be a rank-1 Kokkos::View.");
  // Get a 0-D subview of the entry of the array, and copy to host scalar.
  typename ViewType::non_const_value_type val;
  // DEEP_COPY REVIEW - DEVICE-TO-VALUE
  Kokkos::deep_copy(execution_space(), val, Kokkos::subview(x, ind));
  return val;
}

template <class ViewType,
          class IndexType>
typename ViewType::host_mirror_type::const_type
getEntriesOnHost(const ViewType& x,
                 const IndexType ind,
                 const int count) {
  static_assert(ViewType::rank == 1, "x must be a rank-1 Kokkos::View.");
  // Get a 1-D subview of the entry of the array, and copy to host.
  auto subview = Kokkos::subview(x, Kokkos::make_pair(ind, ind + count));
  return Kokkos::create_mirror_view_and_copy(typename ViewType::host_mirror_type::memory_space(), subview);
}

}  // namespace Details
}  // namespace Tpetra

#endif  // TPETRA_DETAILS_GETENTRYONHOST_HPP