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// TODO: Move into system::cuda

#pragma once

#include <thrust/detail/config.h>

#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 <thrust/detail/cpp_version_check.h>

#if _CCCL_STD_VER >= 2017

#  if _CCCL_HAS_CUDA_COMPILER

#    include <thrust/system/cuda/config.h>

#    include <thrust/detail/alignment.h>
#    include <thrust/detail/static_assert.h>
#    include <thrust/distance.h>
#    include <thrust/iterator/iterator_traits.h>
#    include <thrust/system/cuda/detail/async/copy.h>
#    include <thrust/system/cuda/detail/async/customization.h>
#    include <thrust/system/cuda/detail/sort.h>
#    include <thrust/system/cuda/future.h>
#    include <thrust/type_traits/is_contiguous_iterator.h>
#    include <thrust/type_traits/is_operator_less_or_greater_function_object.h>
#    include <thrust/type_traits/is_trivially_relocatable.h>
#    include <thrust/type_traits/logical_metafunctions.h>

#    include <type_traits>

_CCCL_SUPPRESS_DEPRECATED_PUSH
THRUST_NAMESPACE_BEGIN

namespace system
{
namespace cuda
{
namespace detail
{

// Non-ContiguousIterator input and output iterators
template <typename DerivedPolicy, typename ForwardIt, typename Size, typename StrictWeakOrdering>
auto async_stable_sort_n(execution_policy<DerivedPolicy>& policy, ForwardIt first, Size n, StrictWeakOrdering comp) ->
  typename std::enable_if<negation<is_contiguous_iterator<ForwardIt>>::value, unique_eager_event>::type
{
  using T = typename iterator_traits<ForwardIt>::value_type;

  auto const device_alloc = get_async_device_allocator(policy);

  // Create device-side buffer.

  // FIXME: Combine this temporary allocation with the main one for CUB.
  auto device_buffer = uninitialized_allocate_unique_n<T>(device_alloc, n);

  auto const device_buffer_ptr = device_buffer.get();

  // Synthesize a suitable new execution policy, because we don't want to
  // try and extract twice from the one we were passed.
  typename ::cuda::std::remove_cvref_t<decltype(policy)>::tag_type tag_policy{};

  // Copy from the input into the buffer.

  auto new_policy0 = thrust::detail::derived_cast(policy).rebind_after(std::move(device_buffer));

  THRUST_STATIC_ASSERT((std::tuple_size<decltype(extract_dependencies(policy))>::value + 1
                        <= std::tuple_size<decltype(extract_dependencies(new_policy0))>::value));

  auto f0 = async_copy_n(new_policy0, tag_policy, first, n, device_buffer_ptr);

  // Sort the buffer.

  auto new_policy1 = thrust::detail::derived_cast(policy).rebind_after(std::move(f0));

  THRUST_STATIC_ASSERT((std::tuple_size<decltype(extract_dependencies(policy))>::value + 1
                        <= std::tuple_size<decltype(extract_dependencies(new_policy1))>::value));

  auto f1 = async_sort_n(new_policy1, tag_policy, device_buffer_ptr, n, comp);

  // Copy from the buffer into the input.
  // FIXME: Combine this with the potential memcpy at the end of the main sort
  // routine.

  auto new_policy2 = thrust::detail::derived_cast(policy).rebind_after(std::move(f1));

  THRUST_STATIC_ASSERT((std::tuple_size<decltype(extract_dependencies(policy))>::value + 1
                        <= std::tuple_size<decltype(extract_dependencies(new_policy2))>::value));

  return async_copy_n(new_policy2, tag_policy, device_buffer_ptr, n, first);
}

// ContiguousIterator iterators
// Non-Scalar value type or user-defined StrictWeakOrdering
template <typename DerivedPolicy, typename ForwardIt, typename Size, typename StrictWeakOrdering>
auto async_stable_sort_n(execution_policy<DerivedPolicy>& policy, ForwardIt first, Size n, StrictWeakOrdering comp) ->
  typename std::enable_if<
    conjunction<is_contiguous_iterator<ForwardIt>,
                disjunction<negation<std::is_scalar<typename iterator_traits<ForwardIt>::value_type>>,
                            negation<is_operator_less_or_greater_function_object<StrictWeakOrdering>>>>::value,
    unique_eager_event>::type
{
  auto const device_alloc = get_async_device_allocator(policy);

  unique_eager_event e;

  // Determine temporary device storage requirements.

  size_t tmp_size = 0;
  thrust::cuda_cub::throw_on_error(
    thrust::cuda_cub::__merge_sort::doit_step<
      /* Sort items? */ std::false_type,
      /* Stable? */ std::true_type>(
      nullptr,
      tmp_size,
      first,
      static_cast<std::uint8_t*>(nullptr) // Items.
      ,
      n,
      comp,
      nullptr // Null stream, just for sizing.
      ),
    "after merge sort sizing");

  // Allocate temporary storage.

  auto content = uninitialized_allocate_unique_n<std::uint8_t>(device_alloc, tmp_size);

  // The array was dynamically allocated, so we assume that it's suitably
  // aligned for any type of data. `malloc`/`cudaMalloc`/`new`/`std::allocator`
  // make this guarantee.
  auto const content_ptr = content.get();

  void* const tmp_ptr = static_cast<void*>(raw_pointer_cast(content_ptr));

  // Set up stream with dependencies.

  cudaStream_t const user_raw_stream = thrust::cuda_cub::stream(policy);

  if (thrust::cuda_cub::default_stream() != user_raw_stream)
  {
    e = make_dependent_event(
      std::tuple_cat(std::make_tuple(std::move(content), unique_stream(nonowning, user_raw_stream)),
                     extract_dependencies(std::move(thrust::detail::derived_cast(policy)))));
  }
  else
  {
    e = make_dependent_event(std::tuple_cat(
      std::make_tuple(std::move(content)), extract_dependencies(std::move(thrust::detail::derived_cast(policy)))));
  }

  // Run merge sort.

  thrust::cuda_cub::throw_on_error(
    thrust::cuda_cub::__merge_sort::doit_step<
      /* Sort items? */ std::false_type,
      /* Stable? */ std::true_type>(
      tmp_ptr,
      tmp_size,
      first,
      static_cast<std::uint8_t*>(nullptr) // Items.
      ,
      n,
      comp,
      e.stream().native_handle()),
    "after merge sort sizing");

  return e;
}

template <typename T, typename Size, typename StrictWeakOrdering>
typename std::enable_if<is_operator_less_function_object<StrictWeakOrdering>::value, cudaError_t>::type
invoke_radix_sort(
  cudaStream_t stream, void* tmp_ptr, std::size_t& tmp_size, cub::DoubleBuffer<T>& keys, Size& n, StrictWeakOrdering)
{
  return cub::DeviceRadixSort::SortKeys(tmp_ptr, tmp_size, keys, n, 0, sizeof(T) * 8, stream);
}

template <typename T, typename Size, typename StrictWeakOrdering>
typename std::enable_if<is_operator_greater_function_object<StrictWeakOrdering>::value, cudaError_t>::type
invoke_radix_sort(
  cudaStream_t stream, void* tmp_ptr, std::size_t& tmp_size, cub::DoubleBuffer<T>& keys, Size& n, StrictWeakOrdering)
{
  return cub::DeviceRadixSort::SortKeysDescending(tmp_ptr, tmp_size, keys, n, 0, sizeof(T) * 8, stream);
}

// ContiguousIterator iterators
// Scalar value type
// operator< or operator>
template <typename DerivedPolicy, typename ForwardIt, typename Size, typename StrictWeakOrdering>
auto async_stable_sort_n(execution_policy<DerivedPolicy>& policy, ForwardIt first, Size n, StrictWeakOrdering comp) ->
  typename std::enable_if<conjunction<is_contiguous_iterator<ForwardIt>,
                                      std::is_scalar<typename iterator_traits<ForwardIt>::value_type>,
                                      is_operator_less_or_greater_function_object<StrictWeakOrdering>>::value,
                          unique_eager_event>::type
{
  using T = typename iterator_traits<ForwardIt>::value_type;

  auto const device_alloc = get_async_device_allocator(policy);

  unique_eager_event e;

  cub::DoubleBuffer<T> keys(raw_pointer_cast(&*first), nullptr);

  // Determine temporary device storage requirements.

  size_t tmp_size = 0;
  thrust::cuda_cub::throw_on_error(
    invoke_radix_sort(
      nullptr // Null stream, just for sizing.
      ,
      nullptr,
      tmp_size,
      keys,
      n,
      comp),
    "after radix sort sizing");

  // Allocate temporary storage.

  size_t keys_temp_storage = thrust::detail::aligned_storage_size(sizeof(T) * n, 128);

  auto content = uninitialized_allocate_unique_n<std::uint8_t>(device_alloc, keys_temp_storage + tmp_size);

  // The array was dynamically allocated, so we assume that it's suitably
  // aligned for any type of data. `malloc`/`cudaMalloc`/`new`/`std::allocator`
  // make this guarantee.
  auto const content_ptr = content.get();

  keys.d_buffers[1] = thrust::detail::aligned_reinterpret_cast<T*>(raw_pointer_cast(content_ptr));

  void* const tmp_ptr = static_cast<void*>(raw_pointer_cast(content_ptr + keys_temp_storage));

  // Set up stream with dependencies.

  cudaStream_t const user_raw_stream = thrust::cuda_cub::stream(policy);

  if (thrust::cuda_cub::default_stream() != user_raw_stream)
  {
    e = make_dependent_event(
      std::tuple_cat(std::make_tuple(std::move(content), unique_stream(nonowning, user_raw_stream)),
                     extract_dependencies(std::move(thrust::detail::derived_cast(policy)))));
  }
  else
  {
    e = make_dependent_event(std::tuple_cat(
      std::make_tuple(std::move(content)), extract_dependencies(std::move(thrust::detail::derived_cast(policy)))));
  }

  // Run radix sort.

  thrust::cuda_cub::throw_on_error(
    invoke_radix_sort(e.stream().native_handle(), tmp_ptr, tmp_size, keys, n, comp), "after radix sort launch");

  if (0 != keys.selector)
  {
    auto new_policy0 = thrust::detail::derived_cast(policy).rebind_after(std::move(e));

    THRUST_STATIC_ASSERT((std::tuple_size<decltype(extract_dependencies(policy))>::value + 1
                          <= std::tuple_size<decltype(extract_dependencies(new_policy0))>::value));

    // Synthesize a suitable new execution policy, because we don't want to
    // try and extract twice from the one we were passed.
    typename ::cuda::std::remove_cvref_t<decltype(policy)>::tag_type tag_policy{};

    using return_future = decltype(e);
    return return_future(async_copy_n(new_policy0, tag_policy, keys.d_buffers[1], n, keys.d_buffers[0]));
  }
  else
  {
    return e;
  }
}

} // namespace detail
} // namespace cuda
} // namespace system

namespace cuda_cub
{

// ADL entry point.
template <typename DerivedPolicy, typename ForwardIt, typename Sentinel, typename StrictWeakOrdering>
auto async_stable_sort(execution_policy<DerivedPolicy>& policy, ForwardIt first, Sentinel last, StrictWeakOrdering comp)
  // A GCC 5 bug requires an explicit trailing return type here, so stick with
  // THRUST_DECLTYPE_RETURNS for now.
  THRUST_DECLTYPE_RETURNS(
    thrust::system::cuda::detail::async_stable_sort_n(policy, first, thrust::distance(first, last), comp))

} // namespace cuda_cub

_CCCL_SUPPRESS_DEPRECATED_POP
THRUST_NAMESPACE_END

#  endif // _CCCL_CUDA_COMPILER

#endif
