cuda_toolkit/include/__mdspan/layout_stride.h

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#ifndef _LIBCUDACXX___MDSPAN_LAYOUT_STRIDE_HPP
#define _LIBCUDACXX___MDSPAN_LAYOUT_STRIDE_HPP

#ifndef __cuda_std__
#include <__config>
#endif // __cuda_std__

#include "../__mdspan/compressed_pair.h"
#include "../__mdspan/extents.h"
#include "../__mdspan/macros.h"
#ifdef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
#include "../__mdspan/no_unique_address.h"
#endif
#include "../__mdspan/static_array.h"
#include "../__type_traits/is_same.h"
#include "../__type_traits/is_constructible.h"
#include "../__type_traits/is_convertible.h"
#include "../__type_traits/is_nothrow_constructible.h"
#include "../__type_traits/remove_const.h"
#include "../__utility/integer_sequence.h"
#include "../__utility/move.h"
#include "../algorithm"
#include "../array"
#if __MDSPAN_USE_CONCEPTS && __MDSPAN_HAS_CXX_20
#include "../concepts"
#endif
#include "../numeric"
#include "../span"

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

_LIBCUDACXX_BEGIN_NAMESPACE_STD

#if _LIBCUDACXX_STD_VER > 11

struct layout_left {
  template<class _Extents>
    class mapping;
};
struct layout_right {
  template<class _Extents>
    class mapping;
};

namespace __detail {
  template<class _Layout, class _Mapping>
  constexpr bool __is_mapping_of =
    _CUDA_VSTD::is_same<typename _Layout::template mapping<typename _Mapping::extents_type>, _Mapping>::value;

#if  __MDSPAN_USE_CONCEPTS && __MDSPAN_HAS_CXX_20
  template<class _Mp>
  concept __layout_mapping_alike = requires {
    requires __is_extents<typename _Mp::extents_type>::value;
    { _Mp::is_always_strided() } -> same_as<bool>;
    { _Mp::is_always_exhaustive() } -> same_as<bool>;
    { _Mp::is_always_unique() } -> same_as<bool>;
    bool_constant<_Mp::is_always_strided()>::value;
    bool_constant<_Mp::is_always_exhaustive()>::value;
    bool_constant<_Mp::is_always_unique()>::value;
  };
#endif
} // namespace __detail

struct layout_stride {
  template <class _Extents>
  class mapping
#ifdef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
    : private __detail::__no_unique_address_emulation<
        __detail::__compressed_pair<
          _Extents,
          _CUDA_VSTD::array<typename _Extents::index_type, _Extents::rank()>
        >
      >
#endif
  {
  public:
    using extents_type = _Extents;
    using index_type = typename extents_type::index_type;
    using size_type = typename extents_type::size_type;
    using rank_type = typename extents_type::rank_type;
    using layout_type = layout_stride;

    // This could be a `requires`, but I think it's better and clearer as a `static_assert`.
    static_assert(__detail::__is_extents_v<_Extents>, "layout_stride::mapping must be instantiated with a specialization of _CUDA_VSTD::extents.");


  private:

    //----------------------------------------------------------------------------

    using __strides_storage_t = _CUDA_VSTD::array<index_type, extents_type::rank()>;//_CUDA_VSTD::dextents<index_type, extents_type::rank()>;
    using __member_pair_t = __detail::__compressed_pair<extents_type, __strides_storage_t>;

#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
    _LIBCUDACXX_NO_UNIQUE_ADDRESS __member_pair_t __members;
#else
    using __base_t = __detail::__no_unique_address_emulation<__member_pair_t>;
#endif

    __MDSPAN_FORCE_INLINE_FUNCTION constexpr __strides_storage_t const&
    __strides_storage() const noexcept {
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
      return __members.__second();
#else
      return this->__base_t::__ref().__second();
#endif
    }
    __MDSPAN_FORCE_INLINE_FUNCTION constexpr __strides_storage_t&
    __strides_storage() noexcept {
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
      return __members.__second();
#else
      return this->__base_t::__ref().__second();
#endif
    }

    template<class _SizeType, size_t ... _Ep, size_t ... _Idx>
    _LIBCUDACXX_HOST_DEVICE
    constexpr index_type __get_size(_CUDA_VSTD::extents<_SizeType, _Ep...>,_CUDA_VSTD::integer_sequence<size_t, _Idx...>) const {
      return __MDSPAN_FOLD_TIMES_RIGHT( static_cast<index_type>(extents().extent(_Idx)), 1 );
    }

    //----------------------------------------------------------------------------

    template <class>
    friend class mapping;

    //----------------------------------------------------------------------------

    // Workaround for non-deducibility of the index sequence template parameter if it's given at the top level
    template <class>
    struct __deduction_workaround;

    template <size_t... _Idxs>
    struct __deduction_workaround<_CUDA_VSTD::index_sequence<_Idxs...>>
    {
      template <class _OtherExtents>
      __MDSPAN_INLINE_FUNCTION
      static constexpr bool _eq_impl(mapping const& __self, mapping<_OtherExtents> const& __other) noexcept {
        return    __MDSPAN_FOLD_AND((__self.stride(_Idxs) == __other.stride(_Idxs)) /* && ... */)
               && __MDSPAN_FOLD_AND((__self.extents().extent(_Idxs) == __other.extents().extent(_Idxs)) /* || ... */);
      }
      template <class _OtherExtents>
      __MDSPAN_INLINE_FUNCTION
      static constexpr bool _not_eq_impl(mapping const& __self, mapping<_OtherExtents> const& __other) noexcept {
        return    __MDSPAN_FOLD_OR((__self.stride(_Idxs) != __other.stride(_Idxs)) /* || ... */)
               || __MDSPAN_FOLD_OR((__self.extents().extent(_Idxs) != __other.extents().extent(_Idxs)) /* || ... */);
      }

      template <class... _Integral>
      __MDSPAN_FORCE_INLINE_FUNCTION
      static constexpr size_t _call_op_impl(mapping const& __self, _Integral... __idxs) noexcept {
        return __MDSPAN_FOLD_PLUS_RIGHT((__idxs * __self.stride(_Idxs)), /* + ... + */ 0);
      }

      __MDSPAN_INLINE_FUNCTION
      static constexpr size_t _req_span_size_impl(mapping const& __self) noexcept {
        // assumes no negative strides; not sure if I'm allowed to assume that or not
        return __impl::_call_op_impl(__self, (__self.extents().template __extent<_Idxs>() - 1)...) + 1;
      }

      template<class _OtherMapping>
      __MDSPAN_INLINE_FUNCTION
      static constexpr const __strides_storage_t fill_strides(const _OtherMapping& __map) {
        return __strides_storage_t{static_cast<index_type>(__map.stride(_Idxs))...};
      }

      __MDSPAN_INLINE_FUNCTION
      static constexpr const __strides_storage_t& fill_strides(const __strides_storage_t& __s) {
        return __s;
      }

      template<class _IntegralType>
      __MDSPAN_INLINE_FUNCTION
      static constexpr const __strides_storage_t fill_strides(const _CUDA_VSTD::array<_IntegralType,extents_type::rank()>& __s) {
        return __strides_storage_t{static_cast<index_type>(__s[_Idxs])...};
      }

      template<class _IntegralType>
      __MDSPAN_INLINE_FUNCTION
      static constexpr const __strides_storage_t fill_strides(const _CUDA_VSTD::span<_IntegralType,extents_type::rank()>& __s) {
        return __strides_storage_t{static_cast<index_type>(__s[_Idxs])...};
      }

      __MDSPAN_INLINE_FUNCTION
      static constexpr const __strides_storage_t fill_strides(
        __detail::__extents_to_partially_static_sizes_t<
          _CUDA_VSTD::dextents<index_type, extents_type::rank()>>&& __s) {
        return __strides_storage_t{static_cast<index_type>(__s.template __get_n<_Idxs>())...};
      }

      template<size_t K>
      __MDSPAN_INLINE_FUNCTION
      static constexpr size_t __return_zero() { return 0; }

      template<class _Mapping>
      __MDSPAN_INLINE_FUNCTION
      static constexpr typename _Mapping::index_type
        __OFFSET(const _Mapping& m) { return m(__return_zero<_Idxs>()...); }
    };

    // Can't use defaulted parameter in the __deduction_workaround template because of a bug in MSVC warning C4348.
    using __impl = __deduction_workaround<_CUDA_VSTD::make_index_sequence<_Extents::rank()>>;


    //----------------------------------------------------------------------------

#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
    __MDSPAN_INLINE_FUNCTION constexpr explicit
    mapping(__member_pair_t&& __m) : __members(_CUDA_VSTD::move(__m)) {}
#else
    __MDSPAN_INLINE_FUNCTION constexpr explicit
    mapping(__base_t&& __b) : __base_t(_CUDA_VSTD::move(__b)) {}
#endif

  public: // but not really
    __MDSPAN_INLINE_FUNCTION
    static constexpr mapping
    __make_mapping(
      __detail::__extents_to_partially_static_sizes_t<_Extents>&& __exts,
      __detail::__extents_to_partially_static_sizes_t<
        _CUDA_VSTD::dextents<index_type, _Extents::rank()>>&& __strs
    ) noexcept {
      // call the private constructor we created for this purpose
      return mapping(
#ifdef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
        __base_t{
#endif
          __member_pair_t(
            extents_type::__make_extents_impl(_CUDA_VSTD::move(__exts)),
            __strides_storage_t{__impl::fill_strides(_CUDA_VSTD::move(__strs))}
          )
#ifdef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
        }
#endif
      );
    }
    //----------------------------------------------------------------------------


  public:

    //--------------------------------------------------------------------------------

    __MDSPAN_INLINE_FUNCTION_DEFAULTED constexpr mapping() noexcept = default;
    __MDSPAN_INLINE_FUNCTION_DEFAULTED constexpr mapping(mapping const&) noexcept = default;

    __MDSPAN_TEMPLATE_REQUIRES(
      class _IntegralTypes,
      /* requires */ (
        // MSVC 19.32 does not like using index_type here, requires the typename _Extents::index_type
        // error C2641: cannot deduce template arguments for '_CUDA_VSTD::layout_stride::mapping'
        _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, const remove_const_t<_IntegralTypes>&, typename _Extents::index_type) &&
        _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, typename _Extents::index_type, const remove_const_t<_IntegralTypes>&)
      )
    )
    __MDSPAN_INLINE_FUNCTION
    constexpr
    mapping(
      extents_type const& __e,
      _CUDA_VSTD::array<_IntegralTypes, extents_type::rank()> const& __s
    ) noexcept
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
      : __members{
#else
      : __base_t(__base_t{__member_pair_t(
#endif
          __e, __strides_storage_t(__impl::fill_strides(__s))
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
        }
#else
        )})
#endif
    {
      /*
       * TODO: check preconditions
       * - __s[i] > 0 is true for all i in the range [0, rank_ ).
       * - REQUIRED-SPAN-SIZE(__e, __s) is a representable value of type index_type ([basic.fundamental]).
       * - If rank_ is greater than 0, then there exists a permutation P of the integers in the
       *   range [0, rank_), such that __s[ pi ] >= __s[ pi − 1 ] * __e.extent( pi − 1 ) is true for
       *   all i in the range [1, rank_ ), where pi is the ith element of P.
       */
    }

    __MDSPAN_TEMPLATE_REQUIRES(
      class _IntegralTypes,
      /* requires */ (
        // MSVC 19.32 does not like using index_type here, requires the typename _Extents::index_type
        // error C2641: cannot deduce template arguments for '_CUDA_VSTD::layout_stride::mapping'
        _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, const remove_const_t<_IntegralTypes>&, typename _Extents::index_type) &&
        _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, typename _Extents::index_type, const remove_const_t<_IntegralTypes>&)
      )
    )
    __MDSPAN_INLINE_FUNCTION
    constexpr
    mapping(
      extents_type const& __e,
      _CUDA_VSTD::span<_IntegralTypes, extents_type::rank()> const& __s
    ) noexcept
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
      : __members{
#else
      : __base_t(__base_t{__member_pair_t(
#endif
          __e, __strides_storage_t(__impl::fill_strides(__s))
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
        }
#else
        )})
#endif
    {
      /*
       * TODO: check preconditions
       * - __s[i] > 0 is true for all i in the range [0, rank_ ).
       * - REQUIRED-SPAN-SIZE(__e, __s) is a representable value of type index_type ([basic.fundamental]).
       * - If rank_ is greater than 0, then there exists a permutation P of the integers in the
       *   range [0, rank_), such that __s[ pi ] >= __s[ pi − 1 ] * __e.extent( pi − 1 ) is true for
       *   all i in the range [1, rank_ ), where pi is the ith element of P.
       */
    }

#if !(__MDSPAN_USE_CONCEPTS && __MDSPAN_HAS_CXX_20)
    __MDSPAN_TEMPLATE_REQUIRES(
      class _StridedLayoutMapping,
      /* requires */ (
        _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, extents_type, typename _StridedLayoutMapping::extents_type) &&
        __detail::__is_mapping_of<typename _StridedLayoutMapping::layout_type, _StridedLayoutMapping> &&
        _StridedLayoutMapping::is_always_unique() &&
        _StridedLayoutMapping::is_always_strided()
      )
    )
#else
    template<class _StridedLayoutMapping>
    requires(
         __detail::__layout_mapping_alike<_StridedLayoutMapping> &&
         _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, extents_type, typename _StridedLayoutMapping::extents_type) &&
         _StridedLayoutMapping::is_always_unique() &&
         _StridedLayoutMapping::is_always_strided()
    )
#endif
    __MDSPAN_CONDITIONAL_EXPLICIT(
      (!_CUDA_VSTD::is_convertible<typename _StridedLayoutMapping::extents_type, extents_type>::value) &&
      (__detail::__is_mapping_of<layout_left, _StridedLayoutMapping> ||
       __detail::__is_mapping_of<layout_right, _StridedLayoutMapping> ||
       __detail::__is_mapping_of<layout_stride, _StridedLayoutMapping>)
    ) // needs two () due to comma
    __MDSPAN_INLINE_FUNCTION constexpr
    mapping(_StridedLayoutMapping const& __other) noexcept // NOLINT(google-explicit-constructor)
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
      : __members{
#else
      : __base_t(__base_t{__member_pair_t(
#endif
          __other.extents(), __strides_storage_t(__impl::fill_strides(__other))
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
        }
#else
        )})
#endif
    {
      /*
       * TODO: check preconditions
       * - __other.stride(i) > 0 is true for all i in the range [0, rank_ ).
       * - __other.required_span_size() is a representable value of type index_type ([basic.fundamental]).
       * - OFFSET(__other) == 0
       */
    }

    //--------------------------------------------------------------------------------

    __MDSPAN_INLINE_FUNCTION_DEFAULTED __MDSPAN_CONSTEXPR_14_DEFAULTED
    mapping& operator=(mapping const&) noexcept = default;

    __MDSPAN_INLINE_FUNCTION constexpr const extents_type& extents() const noexcept {
#ifndef _LIBCUDACXX_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
      return __members.__first();
#else
      return this->__base_t::__ref().__first();
#endif
    };

    __MDSPAN_INLINE_FUNCTION
    constexpr _CUDA_VSTD::array< index_type, extents_type::rank() > strides() const noexcept {
      return __strides_storage();
    }

    __MDSPAN_INLINE_FUNCTION
    constexpr index_type required_span_size() const noexcept {
      index_type __span_size = 1;
      for(unsigned __r = 0; __r < extents_type::rank(); __r++) {
        // Return early if any of the extents are zero
        if(extents().extent(__r)==0) return 0;
        __span_size += ( static_cast<index_type>(extents().extent(__r) - 1 ) * __strides_storage()[__r]);
      }
      return __span_size;
    }


    __MDSPAN_TEMPLATE_REQUIRES(
      class... _Indices,
      /* requires */ (
        sizeof...(_Indices) == _Extents::rank() &&
        __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _Indices, index_type) /*&& ...*/ ) &&
        __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _Indices) /*&& ...*/)
      )
    )
    __MDSPAN_FORCE_INLINE_FUNCTION
    constexpr index_type operator()(_Indices... __idxs) const noexcept {
      // Should the op_impl operate in terms of `index_type` rather than `size_t`?
      // Casting `size_t` to `index_type` here.
      return static_cast<index_type>(__impl::_call_op_impl(*this, static_cast<index_type>(__idxs)...));
    }

    __MDSPAN_INLINE_FUNCTION static constexpr bool is_always_unique() noexcept { return true; }
    __MDSPAN_INLINE_FUNCTION static constexpr bool is_always_exhaustive() noexcept {
      return false;
    }
    __MDSPAN_INLINE_FUNCTION static constexpr bool is_always_strided() noexcept { return true; }

    __MDSPAN_INLINE_FUNCTION static constexpr bool is_unique() noexcept { return true; }
    __MDSPAN_INLINE_FUNCTION constexpr bool is_exhaustive() const noexcept {
      return required_span_size() == __get_size( extents(), _CUDA_VSTD::make_index_sequence<extents_type::rank()>());
    }
    __MDSPAN_INLINE_FUNCTION static constexpr bool is_strided() noexcept { return true; }


    __MDSPAN_TEMPLATE_REQUIRES(
      class _Ext = _Extents,
      /* requires */ (
        _Ext::rank() > 0
      )
    )
    __MDSPAN_INLINE_FUNCTION
    constexpr index_type stride(rank_type __r) const noexcept {
      return __strides_storage()[__r];
    }

#if !(__MDSPAN_USE_CONCEPTS && __MDSPAN_HAS_CXX_20)
    __MDSPAN_TEMPLATE_REQUIRES(
      class _StridedLayoutMapping,
      /* requires */ (
        __detail::__is_mapping_of<typename _StridedLayoutMapping::layout_type, _StridedLayoutMapping> &&
        (extents_type::rank() == _StridedLayoutMapping::extents_type::rank()) &&
        _StridedLayoutMapping::is_always_strided()
      )
    )
#else
    template<class _StridedLayoutMapping>
    requires(
         __detail::__layout_mapping_alike<_StridedLayoutMapping> &&
         (extents_type::rank() == _StridedLayoutMapping::extents_type::rank()) &&
         _StridedLayoutMapping::is_always_strided()
    )
#endif
    __MDSPAN_INLINE_FUNCTION
    friend constexpr bool operator==(const mapping& __x, const _StridedLayoutMapping& __y) noexcept {
      bool __strides_match = true;
      for(rank_type __r = 0; __r < extents_type::rank(); __r++)
        __strides_match = __strides_match && (__x.stride(__r) == __y.stride(__r));
      return (__x.extents() == __y.extents()) &&
             (__impl::__OFFSET(__y)== static_cast<typename _StridedLayoutMapping::index_type>(0)) &&
             __strides_match;
    }

    // This one is not technically part of the proposal. Just here to make implementation a bit more optimal hopefully
    __MDSPAN_TEMPLATE_REQUIRES(
      class _OtherExtents,
      /* requires */ (
        (extents_type::rank() == _OtherExtents::rank())
      )
    )
    __MDSPAN_INLINE_FUNCTION
    friend constexpr bool operator==(mapping const& __lhs, mapping<_OtherExtents> const& __rhs) noexcept {
      return __impl::_eq_impl(__lhs, __rhs);
    }

#if !__MDSPAN_HAS_CXX_20
    __MDSPAN_TEMPLATE_REQUIRES(
      class _StridedLayoutMapping,
      /* requires */ (
        __detail::__is_mapping_of<typename _StridedLayoutMapping::layout_type, _StridedLayoutMapping> &&
        (extents_type::rank() == _StridedLayoutMapping::extents_type::rank()) &&
        _StridedLayoutMapping::is_always_strided()
      )
    )
    __MDSPAN_INLINE_FUNCTION
    friend constexpr bool operator!=(const mapping& __x, const _StridedLayoutMapping& __y) noexcept {
      return not (__x == __y);
    }

    __MDSPAN_TEMPLATE_REQUIRES(
      class _OtherExtents,
      /* requires */ (
        (extents_type::rank() == _OtherExtents::rank())
      )
    )
    __MDSPAN_INLINE_FUNCTION
    friend constexpr bool operator!=(mapping const& __lhs, mapping<_OtherExtents> const& __rhs) noexcept {
      return __impl::_not_eq_impl(__lhs, __rhs);
    }
#endif

  };
};

#endif // _LIBCUDACXX_STD_VER > 11

_LIBCUDACXX_END_NAMESPACE_STD

#endif // _LIBCUDACXX___MDSPAN_LAYOUT_STRIDE_HPP