src/gromacs/mdspan/accessor_policy.h

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  40 /*
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  78 /*! \libinternal \file
  79  * \brief Declares accessor policies for mdspan.
  80  *
  81  * Implement ways how to convert a linear offset from a pointer to memory access.
  82  * \author David Hollman <dshollm@sandia.gov>
  83  * \author Christian Blau <cblau@gwdg.de>
  84  * \libinternal
  85  * \ingroup mdspan
  86  */
  87 #ifndef MDSPAN_ACCESSOR_POLICY_H
  88 #define MDSPAN_ACCESSOR_POLICY_H
  89
  90 #include <cstddef>
  91
  92 namespace gmx
  93 {
  94
  95 /*! \libinternal \brief The most basic memory access model for mdspan.
  96  * \tparam ElementType the type held in memory to be accessed
  97  */
  98 template<class ElementType>
  99 class accessor_basic
 100 {
 101     public:
 102         //! Type of element to be accessed.
 103         using element_type  = ElementType;
 104         //! Pointer to element to be accessed.
 105         using pointer       = ElementType*;
 106         //! How to determine a memory offset, provided by self accessor.
 107         using offset_policy = accessor_basic;
 108         //! Type of references.
 109         using reference     = ElementType&;
 110
 111         /*! \brief Shift a pointer by an offset.
 112          * \param[in] p Pointer to reference memory location.
 113          * \param[in] i offset from memory location.
 114          * \returns pointer to offset memory location.
 115          */
 116         constexpr typename offset_policy::pointer
 117         offset( pointer p, ptrdiff_t i ) const noexcept
 118         { return typename offset_policy::pointer(p+i); }
 119
 120         /*! \brief Access element from an offset to given pointer.
 121          * \param[in] p Pointer to reference memory location.
 122          * \param[in] i offset from memory location.
 123          * \returns reference to element stored at offset from memory location.
 124          */
 125         constexpr reference access( pointer p, ptrdiff_t i ) const noexcept
 126         { return p[i]; }
 127
 128         /*! \brief Decay pointer to pointer to ElementType.
 129          * NOTE This function does nothing, because it is the trivial implementation of an accessor.
 130          * \returns input pointer as pointer to ElementType
 131          */
 132         constexpr ElementType* decay( pointer p ) const noexcept
 133         { return p; }
 134 };
 135
 136 }      // namespace gmx
 137 #endif /* end of include guard: MDSPAN_ACCESSOR_POLICY_H */