Tpetra_Details_Blas.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_BLAS_HPP
#define TPETRA_DETAILS_BLAS_HPP


#include "TpetraCore_config.h"
#include "Kokkos_Core.hpp"
#include "Kokkos_Complex.hpp"
#include <type_traits>

namespace Tpetra {
namespace Details {
namespace Blas {

template<class ScalarType>
struct BlasSupportsScalar {
  static constexpr bool value =
    std::is_same<ScalarType, float>::value ||
    std::is_same<ScalarType, double>::value ||
    std::is_same<ScalarType, ::Kokkos::complex<float> >::value ||
    std::is_same<ScalarType, ::Kokkos::complex<double> >::value;
};

template<class LayoutType>
struct BlasSupportsLayout {
  static constexpr bool value =
    std::is_same<LayoutType, ::Kokkos::LayoutLeft>::value;
};

template<class ViewType,
         class IndexType = int>
IndexType
getStride2DView (const ViewType& A)
{
  static_assert (ViewType::rank == 2, "A must be a rank-2 Kokkos::View.");
  static_assert (std::is_same<typename ViewType::array_layout, Kokkos::LayoutLeft>::value ||
                 std::is_same<typename ViewType::array_layout, Kokkos::LayoutRight>::value ||
                 std::is_same<typename ViewType::array_layout, Kokkos::LayoutStride>::value,
                 "A's layout must be either LayoutLeft, LayoutRight, or LayoutStride.");
  static_assert (std::is_integral<IndexType>::value,
                 "IndexType must be a built-in integer type.");
  IndexType stride[8];
  A.stride (stride);
  // BLAS implementations do not like zero LDA, even if (e.g.,) the
  // number of rows is actually zero.  See e.g., GitHub Issue #3235.
  const auto LDA = (A.extent (1) > 1) ? stride[1] : A.extent (0);
  return LDA == 0 ? IndexType (1) : LDA;
}

namespace Impl {

template<class ViewType,
         class ArrayLayout,
         class IndexType>
struct GetStride1DView {
  typedef ArrayLayout array_layout;

  static IndexType getStride (const ViewType& x)
  {
    static_assert (ViewType::rank == 1, "x must be a rank-1 Kokkos::View.");
    static_assert (std::is_same<typename ViewType::array_layout, Kokkos::LayoutLeft>::value ||
                   std::is_same<typename ViewType::array_layout, Kokkos::LayoutRight>::value ||
                   std::is_same<typename ViewType::array_layout, Kokkos::LayoutStride>::value,
                   "x's layout must be either LayoutLeft, LayoutRight, or LayoutStride.");
    static_assert (std::is_same<typename ViewType::array_layout, array_layout>::value,
                   "ViewType::array_layout must be the same as array_layout.");
    static_assert (std::is_integral<IndexType>::value,
                   "IndexType must be a built-in integer type.");
    IndexType stride[8];
    x.stride (stride);
    return stride[0];
  }
};

template<class ViewType,
         class IndexType>
struct GetStride1DView<ViewType, Kokkos::LayoutLeft, IndexType> {
  typedef Kokkos::LayoutLeft array_layout;

  static IndexType getStride (const ViewType&)
  {
    static_assert (ViewType::rank == 1, "x must be a rank-1 Kokkos::View.");
    static_assert (std::is_same<typename ViewType::array_layout, array_layout>::value,
                   "ViewType::array_layout must be the same as array_layout.");
    static_assert (std::is_integral<IndexType>::value,
                   "IndexType must be a built-in integer type.");
    return static_cast<IndexType> (1);
  }
};

template<class ViewType,
         class IndexType>
struct GetStride1DView<ViewType, Kokkos::LayoutRight, IndexType> {
  typedef Kokkos::LayoutRight array_layout;

  static IndexType getStride (const ViewType&)
  {
    static_assert (ViewType::rank == 1, "x must be a rank-1 Kokkos::View.");
    static_assert (std::is_same<typename ViewType::array_layout, array_layout>::value,
                   "ViewType::array_layout must be the same as array_layout.");
    static_assert (std::is_integral<IndexType>::value,
                   "IndexType must be a built-in integer type.");
    return static_cast<IndexType> (1);
  }
};

} // namespace Impl

template<class ViewType,
         class IndexType = int>
IndexType
getStride1DView (const ViewType& x)
{
  typedef Impl::GetStride1DView<ViewType, typename ViewType::array_layout, IndexType> impl_type;
  return impl_type::getStride (x);
}

} // namespace Blas
} // namespace Details
} // namespace Tpetra

#endif // TPETRA_DETAILS_BLAS_HPP