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#ifndef _LIBCUDACXX___MDSPAN_COMPRESSED_PAIR_HPP
#define _LIBCUDACXX___MDSPAN_COMPRESSED_PAIR_HPP

#include <cuda/std/detail/__config>

#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

#include <cuda/std/__mdspan/macros.h>
#ifdef _CCCL_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
#  include <cuda/std/__mdspan/no_unique_address.h>
#endif // _CCCL_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS
#include <cuda/std/__type_traits/enable_if.h>
#include <cuda/std/__type_traits/is_empty.h>

_LIBCUDACXX_BEGIN_NAMESPACE_STD

#if _CCCL_STD_VER > 2011

namespace __detail
{

// For no unique address emulation, this is the case taken when neither are empty.
// For real `[[no_unique_address]]`, this case is always taken.
template <class _Tp, class _Up, class _Enable = void>
struct __compressed_pair
{
  _CCCL_NO_UNIQUE_ADDRESS _Tp __t_val;
  _CCCL_NO_UNIQUE_ADDRESS _Up __u_val;
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp& __first() noexcept
  {
    return __t_val;
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp const& __first() const noexcept
  {
    return __t_val;
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up& __second() noexcept
  {
    return __u_val;
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up const& __second() const noexcept
  {
    return __u_val;
  }

  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair() noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  ~__compressed_pair() noexcept = default;
  template <class _TLike, class _ULike>
  __MDSPAN_INLINE_FUNCTION constexpr __compressed_pair(_TLike&& __t, _ULike&& __u)
      : __t_val((_TLike&&) __t)
      , __u_val((_ULike&&) __u)
  {}
};

#  ifdef _CCCL_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS

// First empty.
template <class _Tp, class _Up>
struct __compressed_pair<
  _Tp,
  _Up,
  _CUDA_VSTD::enable_if_t<_CCCL_TRAIT(_CUDA_VSTD::is_empty, _Tp) && !_CCCL_TRAIT(_CUDA_VSTD::is_empty, _Up)>>
    : private _Tp
{
  _Up __u_val;
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp& __first() noexcept
  {
    return *static_cast<_Tp*>(this);
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp const& __first() const noexcept
  {
    return *static_cast<_Tp const*>(this);
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up& __second() noexcept
  {
    return __u_val;
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up const& __second() const noexcept
  {
    return __u_val;
  }

  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair() noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  ~__compressed_pair() noexcept = default;
  template <class _TLike, class _ULike>
  __MDSPAN_INLINE_FUNCTION constexpr __compressed_pair(_TLike&& __t, _ULike&& __u)
      : _Tp((_TLike&&) __t)
      , __u_val((_ULike&&) __u)
  {}
};

// Second empty.
template <class _Tp, class _Up>
struct __compressed_pair<
  _Tp,
  _Up,
  _CUDA_VSTD::enable_if_t<!_CCCL_TRAIT(_CUDA_VSTD::is_empty, _Tp) && _CCCL_TRAIT(_CUDA_VSTD::is_empty, _Up)>>
    : private _Up
{
  _Tp __t_val;
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp& __first() noexcept
  {
    return __t_val;
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp const& __first() const noexcept
  {
    return __t_val;
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up& __second() noexcept
  {
    return *static_cast<_Up*>(this);
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up const& __second() const noexcept
  {
    return *static_cast<_Up const*>(this);
  }

  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair() noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  ~__compressed_pair() noexcept = default;

  template <class _TLike, class _ULike>
  __MDSPAN_INLINE_FUNCTION constexpr __compressed_pair(_TLike&& __t, _ULike&& __u)
      : _Up((_ULike&&) __u)
      , __t_val((_TLike&&) __t)
  {}
};

// Both empty.
template <class _Tp, class _Up>
struct __compressed_pair<
  _Tp,
  _Up,
  _CUDA_VSTD::enable_if_t<_CCCL_TRAIT(_CUDA_VSTD::is_empty, _Tp) && _CCCL_TRAIT(_CUDA_VSTD::is_empty, _Up)>>
// We need to use the __no_unique_address_emulation wrapper here to avoid
// base class ambiguities.
#    ifdef __MDSPAN_COMPILER_MSVC
    // MSVC doesn't allow you to access public static member functions of a type
    // when you *happen* to privately inherit from that type.
    : protected __no_unique_address_emulation<_Tp, 0>
    , protected __no_unique_address_emulation<_Up, 1>
#    else
    : private __no_unique_address_emulation<_Tp, 0>
    , private __no_unique_address_emulation<_Up, 1>
#    endif
{
  using __first_base_t  = __no_unique_address_emulation<_Tp, 0>;
  using __second_base_t = __no_unique_address_emulation<_Up, 1>;

  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp& __first() noexcept
  {
    return this->__first_base_t::__ref();
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp const& __first() const noexcept
  {
    return this->__first_base_t::__ref();
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up& __second() noexcept
  {
    return this->__second_base_t::__ref();
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Up const& __second() const noexcept
  {
    return this->__second_base_t::__ref();
  }

  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair() noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __compressed_pair(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair const&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __compressed_pair& operator=(__compressed_pair&&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  ~__compressed_pair() noexcept = default;
  template <class _TLike, class _ULike>
  __MDSPAN_INLINE_FUNCTION constexpr __compressed_pair(_TLike&& __t, _ULike&& __u) noexcept
      : __first_base_t(_Tp((_TLike&&) __t))
      , __second_base_t(_Up((_ULike&&) __u))
  {}
};

#  endif // !_CCCL_HAS_NO_ATTRIBUTE_NO_UNIQUE_ADDRESS

} // end namespace __detail

#endif // _CCCL_STD_VER > 2011

_LIBCUDACXX_END_NAMESPACE_STD

#endif // _LIBCUDACXX___MDSPAN_COMPRESSED_PAIR_HPP