src/gromacs/mdspan/layouts.h

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  40 /*
  41  *                          Kokkos v. 2.0
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  78 /*! \libinternal \file
  79  * \brief Declares gmx::layout_right for mdspan.
  80  *
  81  * \author David Hollman <dshollm@sandia.gov>
  82  * \author Christian Blau <cblau@gwdg.de>
  83  * \ingroup mdspan
  84  */
  85 #ifndef MDSPAN_LAYOUTS_H
  86 #define MDSPAN_LAYOUTS_H
  87 #include <cstddef>
  88
  89 #include <type_traits>
  90
  91 namespace gmx
  92 {
  93
  94 /*! \libinternal \brief Right-aligned array layout indexer.
  95  * Carries the mapping class performing the translation from multidimensional
  96  * index to one-dimensional number.
  97  */
  98 class layout_right
  99 {
 100
 101     public:
 102         /*! \libinternal \brief Mapping from multidimensional indices within extents to 1D index.
 103          * \tparam Extents the extents of the multidimensional integers for the mapping.
 104          */
 105         template<class Extents>
 106         class mapping
 107         {
 108             private:
 109                 //! The extents.
 110                 Extents m_extents;
 111
 112             public:
 113                 //! exposing the type of indices
 114                 using index_type   = ptrdiff_t;
 115                 //! exposing the type of the extents
 116                 using extents_type = Extents;
 117                 //! Default constructor.
 118                 constexpr mapping() noexcept = default;
 119                 //! Default move constructor.
 120                 constexpr mapping( mapping && ) noexcept = default;
 121                 //! Default copy constructor.
 122                 constexpr mapping( const mapping & ) noexcept = default;
 123                 //! Default move assignment
 124                 mapping &operator= ( mapping && ) noexcept = default;
 125                 //! Default copy assignment
 126                 mapping &operator= ( const mapping & ) noexcept = default;
 127                 /*! \brief Construct mapping, setting extents
 128                  * \param[in] ext the extents
 129                  */
 130                 constexpr mapping( const Extents &ext ) noexcept
 131                     : m_extents( ext ) {}
 132                 /*! \brief Return the extents.
 133                  * \returns extents
 134                  */
 135                 constexpr const Extents &extents() const noexcept { return m_extents; }
 136
 137             private:
 138                 /* \brief End recursion helper function for static offset calculation.
 139                  * \param[in] sum The accumulated offset over all dimensions
 140                  * \returns The offset.
 141                  */
 142                 static constexpr index_type
 143                 offset( const size_t /*r*/, const ptrdiff_t sum)
 144                 { return sum; }
 145
 146                 /* \brief Statically calculate offset from index and extent.
 147                  * For a multidimensional index (i0,i1,..,in), in a right memory
 148                  * layout, 'i0' denotes the slowest moving dimension and
 149                  * 'in' the fastest moving dimension.
 150                  * The overall offset within extents N = (N0,..,Nn) is then
 151                  * offest = i0 * N1 * .. * Nn + i1 * N2 * .. * Nn + in-1 * Nn + in
 152                  *        = (((i0*N1+i1)*N2+i2)*N3+i3) ...
 153                  * \param[in] r current rank
 154                  * \param[in] sum current sum up to this rank
 155                  * \param[in] i index
 156                  * \oaram[in] indices The rest of the paramter pack.
 157                  * \returns The offset.
 158                  */
 159                 template<class ... Indices >
 160                 inline constexpr index_type
 161                 offset( const size_t r, ptrdiff_t sum, const index_type i, Indices... indices) const noexcept
 162                 {
 163                     return offset( r+1, sum * m_extents.extent(r) + i, indices ...);
 164                 }
 165
 166             public:
 167                 /*! \brief Return the size of the underlying one-dimensional
 168                  * data structure, so that the mapping is always valid.
 169                  *
 170                  * \returns number of span elements
 171                  */
 172                 constexpr index_type required_span_size() const noexcept
 173                 {
 174                     index_type size = 1;
 175                     for (size_t r = 0; r < m_extents.rank(); r++)
 176                     {
 177                         size *= m_extents.extent(r);
 178                     }
 179                     return size;
 180                 }
 181
 182                 /*! \brief Map the multidimensional indices to 1D.
 183                  * Requires number of indicies have the same dimensionality as the mapping.
 184                  * \tparam Indices type of the indices to be mapped
 185                  * \param[in] indices the indices to be mapped
 186                  * \returns One-dimensional integer index.
 187                  */
 188                 template<class ... Indices >
 189                 std::enable_if_t<sizeof ... (Indices) == Extents::rank(), index_type>
 190                 constexpr operator()( Indices ... indices ) const noexcept
 191                 { return offset( 0, 0, indices ... ); }
 192
 193                 //! Report that this mapping is always unique.
 194                 static constexpr bool is_always_unique()     noexcept { return true; }
 195                 //! Report that this mapping is always contiguous.
 196                 static constexpr bool is_always_contiguous() noexcept { return true; }
 197                 //! Report that this mapping is always strided.
 198                 static constexpr bool is_always_strided()    noexcept { return true; }
 199
 200                 //! Report that this mapping is unique.
 201                 constexpr bool is_unique()     const noexcept { return true; }
 202                 //! Report that this mapping is contiguous.
 203                 constexpr bool is_contiguous() const noexcept { return true; }
 204                 //! Report that this mapping is strided.
 205                 constexpr bool is_strided()    const noexcept { return true; }
 206                 /*!\brief Return the stride of dimension r.
 207                  * \param[in] R rank of the stride to be queried.
 208                  * \returns the stride along dimension r.
 209                  */
 210                 constexpr index_type stride(const size_t R) const noexcept
 211                 {
 212                     ptrdiff_t stride = 1;
 213                     for (size_t r = m_extents.rank()-1; r > R; r--)
 214                     {
 215                         stride *= m_extents.extent(r);
 216                     }
 217                     return stride;
 218                 }
 219
 220         }; // class mapping
 221
 222 };         // class layout_right
 223
 224 }          // namespace gmx
 225 #endif     /* end of include guard: MDSPAN_LAYOUTS_H */