Tpetra_KokkosRefactor_Details_MultiVectorLocalDeepCopy.hpp

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

#ifndef TPETRA_KOKKOS_REFACTOR_DETAILS_MULTI_VECTOR_LOCAL_DEEP_COPY_HPP
#define TPETRA_KOKKOS_REFACTOR_DETAILS_MULTI_VECTOR_LOCAL_DEEP_COPY_HPP

#include "Kokkos_Core.hpp"
#include "Tpetra_Details_copyConvert.hpp"

namespace Tpetra {
namespace Details {

namespace {  // (anonymous)

template <class DstViewType, class SrcViewType>
void copyConvertResolvingPossibleAliasing(const DstViewType& dst,
                                          const SrcViewType& src) {
  // NOTE: It's important to do the addition _inside_ the
  // reinterpret-cast.  If you reinterpret_cast the separate results,
  // you may get the wrong answer (e.g., because ptrdiff_t is signed,
  // and pointers may have arbitrary 64-bit virtual addresses).  I'm
  // speaking from experience here.
  const ptrdiff_t dst_beg = reinterpret_cast<ptrdiff_t>(dst.data());
  const ptrdiff_t dst_end =
      reinterpret_cast<ptrdiff_t>(dst.data() + dst.span());
  const ptrdiff_t src_beg = reinterpret_cast<ptrdiff_t>(src.data());
  const ptrdiff_t src_end =
      reinterpret_cast<ptrdiff_t>(src.data() + src.span());

  if (src_beg == dst_beg && src_end == dst_end) {
    // Do nothing; there's no need to copy
  } else if (dst_end <= src_beg || src_end <= dst_beg) {  // no aliasing
    ::Tpetra::Details::copyConvert(dst, src);
  } else {
    // dst and src alias each other, so we can't call
    // Kokkos::deep_copy(dst,src) directly (Kokkos detects this and
    // throws, at least in debug mode).  Instead, we make temporary
    // host storage (create_mirror always makes a new allocation,
    // unlike create_mirror_view).  Use host because it's cheaper to
    // allocate.  Hopefully users aren't doing aliased copies in a
    // tight loop.
    auto src_copy = Kokkos::create_mirror(Kokkos::HostSpace(), src);

    // DEEP_COPY REVIEW - NOT TESTED
    Kokkos::deep_copy(src_copy, src);
    ::Tpetra::Details::copyConvert(dst, src_copy);
  }
}

}  // namespace

template <class DstViewType,
          class SrcViewType,
          class DstWhichVecsType,
          class SrcWhichVecsType>
void localDeepCopy(const DstViewType& dst,
                   const SrcViewType& src,
                   const bool dstConstStride,
                   const bool srcConstStride,
                   const DstWhichVecsType& dstWhichVecs,
                   const SrcWhichVecsType& srcWhichVecs) {
  using Kokkos::ALL;
  using Kokkos::subview;
  using size_type = typename DstViewType::size_type;

  if (dstConstStride && srcConstStride) {
    copyConvertResolvingPossibleAliasing(dst, src);
  } else {
    const size_type numCols = dstConstStride ? static_cast<size_type>(srcWhichVecs.size()) : static_cast<size_type>(dstWhichVecs.size());
    for (size_type j = 0; j < numCols; ++j) {
      const size_type dst_col = dstConstStride ? j : static_cast<size_type>(dstWhichVecs[j]);
      const auto dst_j        = subview(dst, ALL(), dst_col);
      const size_type src_col = srcConstStride ? j : static_cast<size_type>(srcWhichVecs[j]);
      const auto src_j        = subview(src, ALL(), src_col);

      copyConvertResolvingPossibleAliasing(dst_j, src_j);
    }
  }
}

template <class DstViewType,
          class SrcViewType>
void localDeepCopyConstStride(const DstViewType& dst,
                              const SrcViewType& src) {
  return copyConvertResolvingPossibleAliasing(dst, src);
}

}  // namespace Details
}  // namespace Tpetra

#endif  // TPETRA_KOKKOS_REFACTOR_DETAILS_MULTI_VECTOR_LOCAL_DEEP_COPY_HPP