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#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

#if THRUST_DEVICE_COMPILER == THRUST_DEVICE_COMPILER_NVCC
#  include <thrust/distance.h>
#  include <thrust/swap.h>
#  include <thrust/system/cuda/detail/par_to_seq.h>
#  include <thrust/system/cuda/detail/parallel_for.h>
#  include <thrust/system/cuda/detail/transform.h>

#  include <iterator>

THRUST_NAMESPACE_BEGIN

namespace cuda_cub
{

namespace __swap_ranges
{

template <class ItemsIt1, class ItemsIt2>
struct swap_f
{
  ItemsIt1 items1;
  ItemsIt2 items2;

  typedef typename iterator_traits<ItemsIt1>::value_type value1_type;
  typedef typename iterator_traits<ItemsIt2>::value_type value2_type;

  THRUST_FUNCTION
  swap_f(ItemsIt1 items1_, ItemsIt2 items2_)
      : items1(items1_)
      , items2(items2_)
  {}

  template <class Size>
  void THRUST_DEVICE_FUNCTION operator()(Size idx)
  {
    value1_type item1 = items1[idx];
    value2_type item2 = items2[idx];
    // XXX thrust::swap is buggy
    // if reference_type of ItemIt1/ItemsIt2
    // is a proxy reference, then KABOOM!
    // to avoid this, just copy the value first before swap
    // *todo* specialize on real & proxy references
    using thrust::swap;
    swap(item1, item2);
    items1[idx] = item1;
    items2[idx] = item2;
  }
};
} // namespace __swap_ranges

template <class Derived, class ItemsIt1, class ItemsIt2>
ItemsIt2 _CCCL_HOST_DEVICE
swap_ranges(execution_policy<Derived>& policy, ItemsIt1 first1, ItemsIt1 last1, ItemsIt2 first2)
{
  typedef typename iterator_traits<ItemsIt1>::difference_type size_type;

  size_type num_items = static_cast<size_type>(thrust::distance(first1, last1));

  cuda_cub::parallel_for(policy, __swap_ranges::swap_f<ItemsIt1, ItemsIt2>(first1, first2), num_items);

  return first2 + num_items;
}

} // namespace cuda_cub

THRUST_NAMESPACE_END
#endif