/*
//@HEADER
// ************************************************************************
//
//                        Kokkos v. 2.0
//              Copyright (2019) Sandia Corporation
//
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
// the U.S. Government retains certain rights in this software.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// 3. Neither the name of the Corporation nor the names of the
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY SANDIA CORPORATION "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SANDIA CORPORATION OR THE
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Questions? Contact Christian R. Trott (crtrott@sandia.gov)
//
// ************************************************************************
//@HEADER
*/

#ifndef _LIBCUDACXX___MDSPAN_SUBMDSPAN_HPP
#define _LIBCUDACXX___MDSPAN_SUBMDSPAN_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/dynamic_extent.h>
#include <cuda/std/__mdspan/full_extent_t.h>
#include <cuda/std/__mdspan/layout_left.h>
#include <cuda/std/__mdspan/layout_right.h>
#include <cuda/std/__mdspan/layout_stride.h>
#include <cuda/std/__mdspan/macros.h>
#include <cuda/std/__mdspan/mdspan.h>
#include <cuda/std/__type_traits/conditional.h>
#include <cuda/std/__type_traits/integral_constant.h>
#include <cuda/std/__type_traits/is_convertible.h>
#include <cuda/std/__type_traits/is_same.h>
#include <cuda/std/__type_traits/is_signed.h>
#include <cuda/std/__type_traits/remove_const.h>
#include <cuda/std/__type_traits/remove_reference.h>
#include <cuda/std/__utility/move.h>
#include <cuda/std/__utility/pair.h>
#include <cuda/std/tuple>

_LIBCUDACXX_BEGIN_NAMESPACE_STD

#if _CCCL_STD_VER > 2011

namespace __detail
{

template <size_t _OldExtent, size_t _OldStaticStride, class _Tp>
struct __slice_wrap
{
  _Tp slice;
  size_t old_extent;
  size_t old_stride;
};

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

template <size_t _OldExtent, size_t _OldStaticStride>
__MDSPAN_INLINE_FUNCTION constexpr __slice_wrap<_OldExtent, _OldStaticStride, size_t>
__wrap_slice(size_t __val, size_t __ext, size_t __stride)
{
  return {__val, __ext, __stride};
}

template <size_t _OldExtent, size_t _OldStaticStride, class _IntegerType, _IntegerType _Value0>
__MDSPAN_INLINE_FUNCTION constexpr __slice_wrap<_OldExtent, _OldStaticStride, integral_constant<_IntegerType, _Value0>>
__wrap_slice(size_t __val, size_t __ext, integral_constant<_IntegerType, _Value0> __stride)
{
#  if __MDSPAN_HAS_CXX_17
  if constexpr (_CUDA_VSTD::is_signed_v<_IntegerType>)
  {
    static_assert(_Value0 >= _IntegerType(0), "Invalid slice specifier");
  }
#  endif // __MDSPAN_HAS_CXX_17

  return {__val, __ext, __stride};
}

template <size_t _OldExtent, size_t _OldStaticStride>
__MDSPAN_INLINE_FUNCTION constexpr __slice_wrap<_OldExtent, _OldStaticStride, full_extent_t>
__wrap_slice(full_extent_t __val, size_t __ext, size_t __stride)
{
  return {__val, __ext, __stride};
}

// TODO generalize this to anything that works with get<0> and get<1>
template <size_t _OldExtent, size_t _OldStaticStride>
__MDSPAN_INLINE_FUNCTION constexpr __slice_wrap<_OldExtent, _OldStaticStride, _CUDA_VSTD::tuple<size_t, size_t>>
__wrap_slice(_CUDA_VSTD::tuple<size_t, size_t> const& __val, size_t __ext, size_t __stride)
{
  return {__val, __ext, __stride};
}

template <size_t _OldExtent,
          size_t _OldStaticStride,
          class _IntegerType0,
          _IntegerType0 _Value0,
          class _IntegerType1,
          _IntegerType1 _Value1>
__MDSPAN_INLINE_FUNCTION constexpr __slice_wrap<
  _OldExtent,
  _OldStaticStride,
  _CUDA_VSTD::tuple<integral_constant<_IntegerType0, _Value0>, integral_constant<_IntegerType1, _Value1>>>
__wrap_slice(
  _CUDA_VSTD::tuple<integral_constant<_IntegerType0, _Value0>, integral_constant<_IntegerType1, _Value1>> const& __val,
  size_t __ext,
  size_t __stride)
{
  static_assert(_Value1 >= _Value0, "Invalid slice tuple");
  return {__val, __ext, __stride};
}

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

// a layout right remains a layout right if it is indexed by 0 or more scalars,
// then optionally a pair and finally 0 or more all
template <
  // what we encountered until now preserves the layout right
  bool _Result = true,
  // we only encountered 0 or more scalars, no pair or all
  bool _EncounteredOnlyScalar = true>
struct preserve_layout_right_analysis : integral_constant<bool, _Result>
{
  using layout_type_if_preserved = layout_right;
  using encounter_pair           = preserve_layout_right_analysis<
    // if we encounter a pair, the layout remains a layout right only if it was one before
    // and that only scalars were encountered until now
    _Result && _EncounteredOnlyScalar,
    // if we encounter a pair, we didn't encounter scalars only
    false>;
  using encounter_all = preserve_layout_right_analysis<
    // if we encounter a all, the layout remains a layout right if it was one before
    _Result,
    // if we encounter a all, we didn't encounter scalars only
    false>;
  using encounter_scalar = preserve_layout_right_analysis<
    // if we encounter a scalar, the layout remains a layout right only if it was one before
    // and that only scalars were encountered until now
    _Result && _EncounteredOnlyScalar,
    // if we encounter a scalar, the fact that we encountered scalars only doesn't change
    _EncounteredOnlyScalar>;
};

// a layout left remains a layout left if it is indexed by 0 or more all,
// then optionally a pair and finally 0 or more scalars
template <bool _Result = true, bool _EncounteredOnlyAll = true>
struct preserve_layout_left_analysis : integral_constant<bool, _Result>
{
  using layout_type_if_preserved = layout_left;
  using encounter_pair           = preserve_layout_left_analysis<
    // if we encounter a pair, the layout remains a layout left only if it was one before
    // and that only all were encountered until now
    _Result && _EncounteredOnlyAll,
    // if we encounter a pair, we didn't encounter all only
    false>;
  using encounter_all = preserve_layout_left_analysis<
    // if we encounter a all, the layout remains a layout left only if it was one before
    // and that only all were encountered until now
    _Result && _EncounteredOnlyAll,
    // if we encounter a all, the fact that we encountered scalars all doesn't change
    _EncounteredOnlyAll>;
  using encounter_scalar = preserve_layout_left_analysis<
    // if we encounter a scalar, the layout remains a layout left if it was one before
    _Result,
    // if we encounter a scalar, we didn't encounter scalars only
    false>;
};

struct ignore_layout_preservation : integral_constant<bool, false>
{
  using layout_type_if_preserved = void;
  using encounter_pair           = ignore_layout_preservation;
  using encounter_all            = ignore_layout_preservation;
  using encounter_scalar         = ignore_layout_preservation;
};

template <class _Layout>
struct preserve_layout_analysis : ignore_layout_preservation
{};
template <>
struct preserve_layout_analysis<layout_right> : preserve_layout_right_analysis<>
{};
template <>
struct preserve_layout_analysis<layout_left> : preserve_layout_left_analysis<>
{};

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

template <class _IndexT,
          class _PreserveLayoutAnalysis,
          class _OffsetsArray = __partially_static_sizes<_IndexT, size_t>,
          class _ExtsArray    = __partially_static_sizes<_IndexT, size_t>,
          class _StridesArray = __partially_static_sizes<_IndexT, size_t>,
          class               = _CUDA_VSTD::make_index_sequence<_OffsetsArray::__size>,
          class               = _CUDA_VSTD::make_index_sequence<_ExtsArray::__size>,
          class               = _CUDA_VSTD::make_index_sequence<_StridesArray::__size>>
struct __assign_op_slice_handler;

/* clang-format: off */
template <class _IndexT,
          class _PreserveLayoutAnalysis,
          size_t... _Offsets,
          size_t... _Exts,
          size_t... _Strides,
          size_t... _OffsetIdxs,
          size_t... _ExtIdxs,
          size_t... _StrideIdxs>
struct __assign_op_slice_handler<
  _IndexT,
  _PreserveLayoutAnalysis,
  __partially_static_sizes<_IndexT, size_t, _Offsets...>,
  __partially_static_sizes<_IndexT, size_t, _Exts...>,
  __partially_static_sizes<_IndexT, size_t, _Strides...>,
  _CUDA_VSTD::integer_sequence<size_t, _OffsetIdxs...>,
  _CUDA_VSTD::integer_sequence<size_t, _ExtIdxs...>,
  _CUDA_VSTD::integer_sequence<size_t, _StrideIdxs...>>
{
  // TODO remove this for better compiler performance
  static_assert(__MDSPAN_FOLD_AND((_Strides == dynamic_extent || _Strides > 0) /* && ... */), " ");
  static_assert(__MDSPAN_FOLD_AND((_Offsets == dynamic_extent || _Offsets >= 0) /* && ... */), " ");

  using __offsets_storage_t = __partially_static_sizes<_IndexT, size_t, _Offsets...>;
  using __extents_storage_t = __partially_static_sizes<_IndexT, size_t, _Exts...>;
  using __strides_storage_t = __partially_static_sizes<_IndexT, size_t, _Strides...>;
  __offsets_storage_t __offsets;
  __extents_storage_t __exts;
  __strides_storage_t __strides;

#  ifdef __INTEL_COMPILER
#    if __INTEL_COMPILER <= 1800
  __MDSPAN_INLINE_FUNCTION constexpr __assign_op_slice_handler(__assign_op_slice_handler&& __other) noexcept
      : __offsets(_CUDA_VSTD::move(__other.__offsets))
      , __exts(_CUDA_VSTD::move(__other.__exts))
      , __strides(_CUDA_VSTD::move(__other.__strides))
  {}
  __MDSPAN_INLINE_FUNCTION constexpr __assign_op_slice_handler(
    __offsets_storage_t&& __o, __extents_storage_t&& __e, __strides_storage_t&& __s) noexcept
      : __offsets(_CUDA_VSTD::move(__o))
      , __exts(_CUDA_VSTD::move(__e))
      , __strides(_CUDA_VSTD::move(__s))
  {}
#    endif
#  endif

// Don't define this unless we need it; they have a cost to compile
#  ifndef __MDSPAN_USE_RETURN_TYPE_DEDUCTION
  using __extents_type = _CUDA_VSTD::extents<_IndexT, _Exts...>;
#  endif

  // For size_t slice, skip the extent and stride, but add an offset corresponding to the value
  template <size_t _OldStaticExtent, size_t _OldStaticStride>
  __MDSPAN_FORCE_INLINE_FUNCTION // NOLINT (misc-unconventional-assign-operator)
    constexpr auto
    operator=(__slice_wrap<_OldStaticExtent, _OldStaticStride, size_t>&& __slice) noexcept -> __assign_op_slice_handler<
      _IndexT,
      typename _PreserveLayoutAnalysis::encounter_scalar,
      __partially_static_sizes<_IndexT, size_t, _Offsets..., dynamic_extent>,
      __partially_static_sizes<_IndexT, size_t, _Exts...>,
      __partially_static_sizes<_IndexT, size_t, _Strides...> /* intentional space here to work around ICC bug*/>
  {
    return {__partially_static_sizes<_IndexT, size_t, _Offsets..., dynamic_extent>(
              __construct_psa_from_all_exts_values_tag, __offsets.template __get_n<_OffsetIdxs>()..., __slice.slice),
            _CUDA_VSTD::move(__exts),
            _CUDA_VSTD::move(__strides)};
  }

  // Treat integral_constant slice like size_t slice, but with a compile-time offset.
  // The result's extents_type can't take advantage of that,
  // but it might help for specialized layouts.
  template <size_t _OldStaticExtent, size_t _OldStaticStride, class _IntegerType, _IntegerType _Value0>
  __MDSPAN_FORCE_INLINE_FUNCTION // NOLINT (misc-unconventional-assign-operator)
    constexpr auto
    operator=(__slice_wrap<_OldStaticExtent, _OldStaticStride, integral_constant<_IntegerType, _Value0>>&&) noexcept
    -> __assign_op_slice_handler<
      _IndexT,
      typename _PreserveLayoutAnalysis::encounter_scalar,
      __partially_static_sizes<_IndexT, size_t, _Offsets..., _Value0>,
      __partially_static_sizes<_IndexT, size_t, _Exts...>,
      __partially_static_sizes<_IndexT, size_t, _Strides...> /* intentional space here to work around ICC bug*/>
  {
#  if __MDSPAN_HAS_CXX_17
    if constexpr (_CUDA_VSTD::is_signed_v<_IntegerType>)
    {
      static_assert(_Value0 >= _IntegerType(0), "Invalid slice specifier");
    }
#  endif // __MDSPAN_HAS_CXX_17
    return {__partially_static_sizes<_IndexT, size_t, _Offsets..., _Value0>(
              __construct_psa_from_all_exts_values_tag, __offsets.template __get_n<_OffsetIdxs>()..., size_t(_Value0)),
            _CUDA_VSTD::move(__exts),
            _CUDA_VSTD::move(__strides)};
  }

  // For a _CUDA_VSTD::full_extent, offset 0 and old extent
  template <size_t _OldStaticExtent, size_t _OldStaticStride>
  __MDSPAN_FORCE_INLINE_FUNCTION // NOLINT (misc-unconventional-assign-operator)
    constexpr auto
    operator=(__slice_wrap<_OldStaticExtent, _OldStaticStride, full_extent_t>&& __slice) noexcept
    -> __assign_op_slice_handler<
      _IndexT,
      typename _PreserveLayoutAnalysis::encounter_all,
      __partially_static_sizes<_IndexT, size_t, _Offsets..., 0>,
      __partially_static_sizes<_IndexT, size_t, _Exts..., _OldStaticExtent>,
      __partially_static_sizes<_IndexT,
                               size_t,
                               _Strides...,
                               _OldStaticStride> /* intentional space here to work around ICC bug*/>
  {
    return {
      __partially_static_sizes<_IndexT, size_t, _Offsets..., 0>(
        __construct_psa_from_all_exts_values_tag, __offsets.template __get_n<_OffsetIdxs>()..., size_t(0)),
      __partially_static_sizes<_IndexT, size_t, _Exts..., _OldStaticExtent>(
        __construct_psa_from_all_exts_values_tag, __exts.template __get_n<_ExtIdxs>()..., __slice.old_extent),
      __partially_static_sizes<_IndexT, size_t, _Strides..., _OldStaticStride>(
        __construct_psa_from_all_exts_values_tag, __strides.template __get_n<_StrideIdxs>()..., __slice.old_stride)};
  }

  // For a _CUDA_VSTD::tuple, add an offset and add a new dynamic extent (strides still preserved)
  template <size_t _OldStaticExtent, size_t _OldStaticStride>
  __MDSPAN_FORCE_INLINE_FUNCTION // NOLINT (misc-unconventional-assign-operator)
    constexpr auto
    operator=(__slice_wrap<_OldStaticExtent, _OldStaticStride, tuple<size_t, size_t>>&& __slice) noexcept
    -> __assign_op_slice_handler<
      _IndexT,
      typename _PreserveLayoutAnalysis::encounter_pair,
      __partially_static_sizes<_IndexT, size_t, _Offsets..., dynamic_extent>,
      __partially_static_sizes<_IndexT, size_t, _Exts..., dynamic_extent>,
      __partially_static_sizes<_IndexT,
                               size_t,
                               _Strides...,
                               _OldStaticStride> /* intentional space here to work around ICC bug*/>
  {
    return {
      __partially_static_sizes<_IndexT, size_t, _Offsets..., dynamic_extent>(
        __construct_psa_from_all_exts_values_tag,
        __offsets.template __get_n<_OffsetIdxs>()...,
        _CUDA_VSTD::get<0>(__slice.slice)),
      __partially_static_sizes<_IndexT, size_t, _Exts..., dynamic_extent>(
        __construct_psa_from_all_exts_values_tag,
        __exts.template __get_n<_ExtIdxs>()...,
        _CUDA_VSTD::get<1>(__slice.slice) - _CUDA_VSTD::get<0>(__slice.slice)),
      __partially_static_sizes<_IndexT, size_t, _Strides..., _OldStaticStride>(
        __construct_psa_from_all_exts_values_tag, __strides.template __get_n<_StrideIdxs>()..., __slice.old_stride)};
  }

  // For a _CUDA_VSTD::tuple of two integral_constant, do something like
  // we did above for a tuple of two size_t, but make sure the
  // result's extents type make the values compile-time constants.
  template <size_t _OldStaticExtent,
            size_t _OldStaticStride,
            class _IntegerType0,
            _IntegerType0 _Value0,
            class _IntegerType1,
            _IntegerType1 _Value1>
  __MDSPAN_FORCE_INLINE_FUNCTION // NOLINT (misc-unconventional-assign-operator)
    constexpr auto
    operator=(__slice_wrap<_OldStaticExtent,
                           _OldStaticStride,
                           tuple<integral_constant<_IntegerType0, _Value0>, integral_constant<_IntegerType1, _Value1>>>&&
                __slice) noexcept
    -> __assign_op_slice_handler<
      _IndexT,
      typename _PreserveLayoutAnalysis::encounter_pair,
      __partially_static_sizes<_IndexT, size_t, _Offsets..., size_t(_Value0)>,
      __partially_static_sizes<_IndexT, size_t, _Exts..., size_t(_Value1 - _Value0)>,
      __partially_static_sizes<_IndexT,
                               size_t,
                               _Strides...,
                               _OldStaticStride> /* intentional space here to work around ICC bug*/>
  {
    static_assert(_Value1 >= _Value0, "Invalid slice specifier");
    return {
      // We're still turning the template parameters _Value0 and _Value1
      // into (constexpr) run-time values here.
      __partially_static_sizes<_IndexT, size_t, _Offsets..., size_t(_Value0)>(
        __construct_psa_from_all_exts_values_tag, __offsets.template __get_n<_OffsetIdxs>()..., _Value0),
      __partially_static_sizes<_IndexT, size_t, _Exts..., size_t(_Value1 - _Value0)>(
        __construct_psa_from_all_exts_values_tag, __exts.template __get_n<_ExtIdxs>()..., _Value1 - _Value0),
      __partially_static_sizes<_IndexT, size_t, _Strides..., _OldStaticStride>(
        __construct_psa_from_all_exts_values_tag, __strides.template __get_n<_StrideIdxs>()..., __slice.old_stride)};
  }

  // TODO defer instantiation of this?
  using layout_type =
    conditional_t<_PreserveLayoutAnalysis::value,
                  typename _PreserveLayoutAnalysis::layout_type_if_preserved,
                  layout_stride>;

  // TODO noexcept specification
  template <class NewLayout>
  __MDSPAN_INLINE_FUNCTION __MDSPAN_DEDUCE_RETURN_TYPE_SINGLE_LINE(
    (constexpr /* auto */
     _make_layout_mapping_impl(NewLayout) noexcept),
    (
      /* not layout stride, so don't pass dynamic_strides */
      /* return */ typename NewLayout::template mapping<_CUDA_VSTD::extents<_IndexT, _Exts...>>(
        extents<_IndexT, _Exts...>::__make_extents_impl(_CUDA_VSTD::move(__exts))) /* ; */
      ))

    __MDSPAN_INLINE_FUNCTION __MDSPAN_DEDUCE_RETURN_TYPE_SINGLE_LINE(
      (constexpr /* auto */
       _make_layout_mapping_impl(layout_stride) noexcept),
      (
        /* return */ layout_stride::template mapping<_CUDA_VSTD::extents<_IndexT, _Exts...>>::__make_mapping(
          _CUDA_VSTD::move(__exts), _CUDA_VSTD::move(__strides)) /* ; */
        ))

      template <class _OldLayoutMapping> // mostly for deferred instantiation, but maybe we'll use this in the future
      __MDSPAN_INLINE_FUNCTION __MDSPAN_DEDUCE_RETURN_TYPE_SINGLE_LINE(
        (constexpr /* auto */
         make_layout_mapping(_OldLayoutMapping const&) noexcept),
        (
          /* return */ this->_make_layout_mapping_impl(layout_type{}) /* ; */
          ))
};

//==============================================================================

#  if __MDSPAN_USE_RETURN_TYPE_DEDUCTION
// Forking this because the C++11 version will be *completely* unreadable
template <class _ET, class _ST, size_t... _Exts, class _LP, class _AP, class... _SliceSpecs, size_t... _Idxs>
__MDSPAN_INLINE_FUNCTION constexpr auto _submdspan_impl(
  _CUDA_VSTD::integer_sequence<size_t, _Idxs...>,
  mdspan<_ET, _CUDA_VSTD::extents<_ST, _Exts...>, _LP, _AP> const& __src,
  _SliceSpecs&&... __slices) noexcept
{
  using __index_t = _ST;
  auto __handled  = __MDSPAN_FOLD_ASSIGN_LEFT(
    (__detail::__assign_op_slice_handler<__index_t, __detail::preserve_layout_analysis<_LP>>{
      __partially_static_sizes<__index_t, size_t>{},
      __partially_static_sizes<__index_t, size_t>{},
      __partially_static_sizes<__index_t, size_t>{}}),
    /* = ... = */
    __detail::__wrap_slice<_Exts, dynamic_extent>(
      __slices, __src.extents().template __extent<_Idxs>(), __src.mapping().stride(_Idxs)));

  size_t __offset_size = __src.mapping()(__handled.__offsets.template __get_n<_Idxs>()...);
  auto __offset_ptr    = __src.accessor().offset(__src.data_handle(), __offset_size);
  auto __map           = __handled.make_layout_mapping(__src.mapping());
  auto __acc_pol       = typename _AP::offset_policy(__src.accessor());
  return mdspan<_ET,
                remove_const_t<_CUDA_VSTD::remove_reference_t<decltype(__map.extents())>>,
                typename decltype(__handled)::layout_type,
                remove_const_t<_CUDA_VSTD::remove_reference_t<decltype(__acc_pol)>>>(
    _CUDA_VSTD::move(__offset_ptr), _CUDA_VSTD::move(__map), _CUDA_VSTD::move(__acc_pol));
}
#  else

template <class _ET, class _AP, class _Src, class _Handled, size_t... _Idxs>
auto _submdspan_impl_helper(_Src&& __src, _Handled&& __h, _CUDA_VSTD::integer_sequence<size_t, _Idxs...>)
  -> mdspan<_ET, typename _Handled::__extents_type, typename _Handled::layout_type, typename _AP::offset_policy>
{
  return {__src.accessor().offset(__src.data_handle(), __src.mapping()(__h.__offsets.template __get_n<_Idxs>()...)),
          __h.make_layout_mapping(__src.mapping()),
          typename _AP::offset_policy(__src.accessor())};
}

template <class _ET, class _ST, size_t... _Exts, class _LP, class _AP, class... _SliceSpecs, size_t... _Idxs>
__MDSPAN_INLINE_FUNCTION __MDSPAN_DEDUCE_RETURN_TYPE_SINGLE_LINE(
  (constexpr /* auto */ _submdspan_impl(_CUDA_VSTD::integer_sequence<size_t, _Idxs...> __seq,
                                        mdspan<_ET, _CUDA_VSTD::extents<_ST, _Exts...>, _LP, _AP> const& __src,
                                        _SliceSpecs&&... __slices) noexcept),
  (
    /* return */ _submdspan_impl_helper<_ET, _AP>(
      __src,
      __MDSPAN_FOLD_ASSIGN_LEFT(
        (__detail::__assign_op_slice_handler<size_t, __detail::preserve_layout_analysis<_LP>>{
          __partially_static_sizes<_ST, size_t>{},
          __partially_static_sizes<_ST, size_t>{},
          __partially_static_sizes<_ST, size_t>{}}),
        /* = ... = */
        __detail::__wrap_slice<_Exts, dynamic_extent>(
          __slices, __src.extents().template __extent<_Idxs>(), __src.mapping().stride(_Idxs))),
      __seq) /* ; */
    ))

#  endif

template <class _Tp>
struct _is_layout_stride : false_type
{};
template <>
struct _is_layout_stride<layout_stride> : true_type
{};

} // namespace __detail

//==============================================================================

__MDSPAN_TEMPLATE_REQUIRES(
  class _ET,
  class _EXT,
  class _LP,
  class _AP,
  class... _SliceSpecs,
  /* requires */
  ((_CCCL_TRAIT(_CUDA_VSTD::is_same, _LP, layout_left) || _CCCL_TRAIT(_CUDA_VSTD::is_same, _LP, layout_right)
    || __detail::_is_layout_stride<_LP>::value)
   && __MDSPAN_FOLD_AND((_CCCL_TRAIT(_CUDA_VSTD::is_convertible, _SliceSpecs, size_t)
                         || _CCCL_TRAIT(_CUDA_VSTD::is_convertible, _SliceSpecs, tuple<size_t, size_t>)
                         || _CCCL_TRAIT(_CUDA_VSTD::is_convertible, _SliceSpecs, full_extent_t)) /* && ... */)
   && sizeof...(_SliceSpecs) == _EXT::rank()))
__MDSPAN_INLINE_FUNCTION
__MDSPAN_DEDUCE_RETURN_TYPE_SINGLE_LINE(
  (constexpr submdspan(mdspan<_ET, _EXT, _LP, _AP> const& __src, _SliceSpecs... __slices) noexcept),
  (
    /* return */
    __detail::_submdspan_impl(_CUDA_VSTD::make_index_sequence<sizeof...(_SliceSpecs)>{}, __src, __slices...) /*;*/
    ))
/* clang-format: on */

#endif // _CCCL_STD_VER > 2011

_LIBCUDACXX_END_NAMESPACE_STD

#endif // _LIBCUDACXX___MDSPAN_SUBMDSPAN_HPP