/******************************************************************************
 * Copyright (c) 2016, NVIDIA CORPORATION.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * 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.
 *     * Neither the name of the NVIDIA CORPORATION nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 NVIDIA CORPORATION BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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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 _CCCL_HAS_CUDA_COMPILER

#  include <thrust/detail/alignment.h>
#  include <thrust/detail/mpl/math.h>
#  include <thrust/detail/temporary_array.h>
#  include <thrust/distance.h>
#  include <thrust/extrema.h>
#  include <thrust/pair.h>
#  include <thrust/set_operations.h>
#  include <thrust/system/cuda/detail/cdp_dispatch.h>
#  include <thrust/system/cuda/detail/core/agent_launcher.h>
#  include <thrust/system/cuda/detail/execution_policy.h>
#  include <thrust/system/cuda/detail/get_value.h>
#  include <thrust/system/cuda/detail/par_to_seq.h>
#  include <thrust/system/cuda/detail/util.h>

#  include <cstdint>

THRUST_NAMESPACE_BEGIN

namespace cuda_cub
{

namespace __set_operations
{

template <bool UpperBound, class IntT, class Size, class It, class T, class Comp>
THRUST_DEVICE_FUNCTION void binary_search_iteration(It data, Size& begin, Size& end, T key, int shift, Comp comp)
{
  IntT scale = (1 << shift) - 1;
  Size mid   = (begin + scale * end) >> shift;

  T key2    = data[mid];
  bool pred = UpperBound ? !comp(key, key2) : comp(key2, key);
  if (pred)
  {
    begin = mid + 1;
  }
  else
  {
    end = mid;
  }
}

template <bool UpperBound, class Size, class T, class It, class Comp>
THRUST_DEVICE_FUNCTION Size binary_search(It data, Size count, T key, Comp comp)
{
  Size begin = 0;
  Size end   = count;
  while (begin < end)
  {
    binary_search_iteration<UpperBound, int>(data, begin, end, key, 1, comp);
  }
  return begin;
}

template <bool UpperBound, class IntT, class Size, class T, class It, class Comp>
THRUST_DEVICE_FUNCTION Size biased_binary_search(It data, Size count, T key, IntT levels, Comp comp)
{
  Size begin = 0;
  Size end   = count;

  if (levels >= 4 && begin < end)
  {
    binary_search_iteration<UpperBound, IntT>(data, begin, end, key, 9, comp);
  }
  if (levels >= 3 && begin < end)
  {
    binary_search_iteration<UpperBound, IntT>(data, begin, end, key, 7, comp);
  }
  if (levels >= 2 && begin < end)
  {
    binary_search_iteration<UpperBound, IntT>(data, begin, end, key, 5, comp);
  }
  if (levels >= 1 && begin < end)
  {
    binary_search_iteration<UpperBound, IntT>(data, begin, end, key, 4, comp);
  }

  while (begin < end)
  {
    binary_search_iteration<UpperBound, IntT>(data, begin, end, key, 1, comp);
  }
  return begin;
}

template <bool UpperBound, class Size, class It1, class It2, class Comp>
THRUST_DEVICE_FUNCTION Size merge_path(It1 a, Size aCount, It2 b, Size bCount, Size diag, Comp comp)
{
  using T = typename thrust::iterator_traits<It1>::value_type;

  Size begin = thrust::max<Size>(0, diag - bCount);
  Size end   = thrust::min<Size>(diag, aCount);

  while (begin < end)
  {
    Size mid  = (begin + end) >> 1;
    T aKey    = a[mid];
    T bKey    = b[diag - 1 - mid];
    bool pred = UpperBound ? comp(aKey, bKey) : !comp(bKey, aKey);
    if (pred)
    {
      begin = mid + 1;
    }
    else
    {
      end = mid;
    }
  }
  return begin;
}

template <class It1, class It2, class Size, class Size2, class CompareOp>
THRUST_DEVICE_FUNCTION pair<Size, Size>
balanced_path(It1 keys1, It2 keys2, Size num_keys1, Size num_keys2, Size diag, Size2 levels, CompareOp compare_op)
{
  using T = typename iterator_traits<It1>::value_type;

  Size index1 = merge_path<false>(keys1, num_keys1, keys2, num_keys2, diag, compare_op);
  Size index2 = diag - index1;

  bool star = false;
  if (index2 < num_keys2)
  {
    T x = keys2[index2];

    // Search for the beginning of the duplicate run in both A and B.
    Size start1 = biased_binary_search<false>(keys1, index1, x, levels, compare_op);
    Size start2 = biased_binary_search<false>(keys2, index2, x, levels, compare_op);

    // The distance between x's merge path and its lower_bound is its rank.
    // We add up the a and b ranks and evenly distribute them to
    // get a stairstep path.
    Size run1      = index1 - start1;
    Size run2      = index2 - start2;
    Size total_run = run1 + run2;

    // Attempt to advance b and regress a.
    Size advance2 = max<Size>(total_run >> 1, total_run - run1);
    Size end2     = min<Size>(num_keys2, start2 + advance2 + 1);

    Size run_end2 = index2 + binary_search<true>(keys2 + index2, end2 - index2, x, compare_op);
    run2          = run_end2 - start2;

    advance2      = min<Size>(advance2, run2);
    Size advance1 = total_run - advance2;

    bool round_up = (advance1 == advance2 + 1) && (advance2 < run2);
    if (round_up)
    {
      star = true;
    }

    index1 = start1 + advance1;
  }
  return thrust::make_pair(index1, (diag - index1) + star);
} // func balanced_path

template <int _BLOCK_THREADS,
          int _ITEMS_PER_THREAD                   = 1,
          cub::BlockLoadAlgorithm _LOAD_ALGORITHM = cub::BLOCK_LOAD_DIRECT,
          cub::CacheLoadModifier _LOAD_MODIFIER   = cub::LOAD_LDG,
          cub::BlockScanAlgorithm _SCAN_ALGORITHM = cub::BLOCK_SCAN_WARP_SCANS>
struct PtxPolicy
{
  enum
  {
    BLOCK_THREADS    = _BLOCK_THREADS,
    ITEMS_PER_THREAD = _ITEMS_PER_THREAD,
    ITEMS_PER_TILE   = _BLOCK_THREADS * _ITEMS_PER_THREAD - 1
  };

  static const cub::BlockLoadAlgorithm LOAD_ALGORITHM = _LOAD_ALGORITHM;
  static const cub::CacheLoadModifier LOAD_MODIFIER   = _LOAD_MODIFIER;
  static const cub::BlockScanAlgorithm SCAN_ALGORITHM = _SCAN_ALGORITHM;
}; // PtxPolicy

template <class Arch, class T, class U>
struct Tuning;

namespace mpl = thrust::detail::mpl::math;

template <class T, class U>
struct Tuning<sm30, T, U>
{
  enum
  {
    MAX_INPUT_BYTES             = mpl::max<size_t, sizeof(T), sizeof(U)>::value,
    COMBINED_INPUT_BYTES        = sizeof(T), // + sizeof(Value),
    NOMINAL_4B_ITEMS_PER_THREAD = 7,
    ITEMS_PER_THREAD =
      mpl::min<int,
               NOMINAL_4B_ITEMS_PER_THREAD,
               mpl::max<int,
                        1,
                        static_cast<int>(((NOMINAL_4B_ITEMS_PER_THREAD * 4) + COMBINED_INPUT_BYTES - 1)
                                         / COMBINED_INPUT_BYTES)>::value>::value,
  };

  using type =
    PtxPolicy<128, ITEMS_PER_THREAD, cub::BLOCK_LOAD_WARP_TRANSPOSE, cub::LOAD_DEFAULT, cub::BLOCK_SCAN_WARP_SCANS>;
}; // tuning sm30

template <class T, class U>
struct Tuning<sm52, T, U>
{
  enum
  {
    MAX_INPUT_BYTES             = mpl::max<size_t, sizeof(T), sizeof(U)>::value,
    COMBINED_INPUT_BYTES        = sizeof(T), // + sizeof(U),
    NOMINAL_4B_ITEMS_PER_THREAD = 15,
    ITEMS_PER_THREAD =
      mpl::min<int,
               NOMINAL_4B_ITEMS_PER_THREAD,
               mpl::max<int,
                        1,
                        static_cast<int>(((NOMINAL_4B_ITEMS_PER_THREAD * 4) + COMBINED_INPUT_BYTES - 1)
                                         / COMBINED_INPUT_BYTES)>::value>::value,
  };

  using type =
    PtxPolicy<256, ITEMS_PER_THREAD, cub::BLOCK_LOAD_WARP_TRANSPOSE, cub::LOAD_DEFAULT, cub::BLOCK_SCAN_WARP_SCANS>;
}; // tuning sm52

template <class T, class U>
struct Tuning<sm60, T, U>
{
  enum
  {
    MAX_INPUT_BYTES             = mpl::max<size_t, sizeof(T), sizeof(U)>::value,
    COMBINED_INPUT_BYTES        = sizeof(T), // + sizeof(U),
    NOMINAL_4B_ITEMS_PER_THREAD = 19,
    ITEMS_PER_THREAD =
      mpl::min<int,
               NOMINAL_4B_ITEMS_PER_THREAD,
               mpl::max<int,
                        1,
                        static_cast<int>(((NOMINAL_4B_ITEMS_PER_THREAD * 4) + COMBINED_INPUT_BYTES - 1)
                                         / COMBINED_INPUT_BYTES)>::value>::value,
  };

  using type =
    PtxPolicy<512, ITEMS_PER_THREAD, cub::BLOCK_LOAD_WARP_TRANSPOSE, cub::LOAD_DEFAULT, cub::BLOCK_SCAN_WARP_SCANS>;
}; // tuning sm60

template <class KeysIt1,
          class KeysIt2,
          class ValuesIt1,
          class ValuesIt2,
          class KeysOutputIt,
          class ValuesOutputIt,
          class Size,
          class CompareOp,
          class SetOp,
          class HAS_VALUES>
struct SetOpAgent
{
  using key1_type   = typename iterator_traits<KeysIt1>::value_type;
  using key2_type   = typename iterator_traits<KeysIt2>::value_type;
  using value1_type = typename iterator_traits<ValuesIt1>::value_type;
  using value2_type = typename iterator_traits<ValuesIt2>::value_type;

  using key_type   = key1_type;
  using value_type = value1_type;

  using ScanTileState = cub::ScanTileState<Size>;

  template <class Arch>
  struct PtxPlan : Tuning<Arch, key_type, value_type>::type
  {
    using tuning = Tuning<Arch, key_type, value_type>;

    using KeysLoadIt1   = typename core::LoadIterator<PtxPlan, KeysIt1>::type;
    using KeysLoadIt2   = typename core::LoadIterator<PtxPlan, KeysIt2>::type;
    using ValuesLoadIt1 = typename core::LoadIterator<PtxPlan, ValuesIt1>::type;
    using ValuesLoadIt2 = typename core::LoadIterator<PtxPlan, ValuesIt2>::type;

    using BlockLoadKeys1   = typename core::BlockLoad<PtxPlan, KeysLoadIt1>::type;
    using BlockLoadKeys2   = typename core::BlockLoad<PtxPlan, KeysLoadIt2>::type;
    using BlockLoadValues1 = typename core::BlockLoad<PtxPlan, ValuesLoadIt1>::type;
    using BlockLoadValues2 = typename core::BlockLoad<PtxPlan, ValuesLoadIt2>::type;

    using TilePrefixCallback = cub::TilePrefixCallbackOp<Size, ::cuda::std::plus<>, ScanTileState, Arch::ver>;

    using BlockScan = cub::BlockScan<Size, PtxPlan::BLOCK_THREADS, PtxPlan::SCAN_ALGORITHM, 1, 1, Arch::ver>;

    // gather required temporary storage in a union
    //
    union TempStorage
    {
      struct ScanStorage
      {
        typename BlockScan::TempStorage scan;
        typename TilePrefixCallback::TempStorage prefix;
      } scan_storage;

      struct LoadStorage
      {
        core::uninitialized_array<int, PtxPlan::BLOCK_THREADS> offset;
        union
        {
          // FIXME These don't appear to be used anywhere?
          typename BlockLoadKeys1::TempStorage load_keys1;
          typename BlockLoadKeys2::TempStorage load_keys2;
          typename BlockLoadValues1::TempStorage load_values1;
          typename BlockLoadValues2::TempStorage load_values2;

          // Allocate extra shmem than truly necessary
          // This will permit to avoid range checks in
          // serial set operations, e.g. serial_set_difference
          core::uninitialized_array<key_type, PtxPlan::ITEMS_PER_TILE + PtxPlan::BLOCK_THREADS> keys_shared;

          core::uninitialized_array<value_type, PtxPlan::ITEMS_PER_TILE + PtxPlan::BLOCK_THREADS> values_shared;
        }; // anon union
      } load_storage; // struct LoadStorage
    }; // union TempStorage
  }; // struct PtxPlan

  using ptx_plan = typename core::specialize_plan_msvc10_war<PtxPlan>::type::type;

  using KeysLoadIt1   = typename ptx_plan::KeysLoadIt1;
  using KeysLoadIt2   = typename ptx_plan::KeysLoadIt2;
  using ValuesLoadIt1 = typename ptx_plan::ValuesLoadIt1;
  using ValuesLoadIt2 = typename ptx_plan::ValuesLoadIt2;

  using BlockLoadKeys1   = typename ptx_plan::BlockLoadKeys1;
  using BlockLoadKeys2   = typename ptx_plan::BlockLoadKeys2;
  using BlockLoadValues1 = typename ptx_plan::BlockLoadValues1;
  using BlockLoadValues2 = typename ptx_plan::BlockLoadValues2;

  using TilePrefixCallback = typename ptx_plan::TilePrefixCallback;
  using BlockScan          = typename ptx_plan::BlockScan;

  using TempStorage = typename ptx_plan::TempStorage;

  enum
  {
    ITEMS_PER_THREAD = ptx_plan::ITEMS_PER_THREAD,
    BLOCK_THREADS    = ptx_plan::BLOCK_THREADS,
  };

  struct impl
  {
    //---------------------------------------------------------------------
    // Per-thread fields
    //---------------------------------------------------------------------

    TempStorage& storage;
    ScanTileState& tile_state;
    KeysLoadIt1 keys1_in;
    KeysLoadIt2 keys2_in;
    ValuesLoadIt1 values1_in;
    ValuesLoadIt2 values2_in;
    Size keys1_count;
    Size keys2_count;
    KeysOutputIt keys_out;
    ValuesOutputIt values_out;
    CompareOp compare_op;
    SetOp set_op;
    pair<Size, Size>* partitions;
    std::size_t* output_count;

    //---------------------------------------------------------------------
    // Utility functions
    //---------------------------------------------------------------------

    template <bool IS_FULL_TILE, class T, class It1, class It2>
    THRUST_DEVICE_FUNCTION void
    gmem_to_reg(T (&output)[ITEMS_PER_THREAD], It1 input1, It2 input2, int count1, int count2)
    {
      if (IS_FULL_TILE)
      {
#  pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD - 1; ++ITEM)
        {
          int idx      = BLOCK_THREADS * ITEM + threadIdx.x;
          output[ITEM] = (idx < count1) ? static_cast<T>(input1[idx]) : static_cast<T>(input2[idx - count1]);
        }

        // last ITEM might be a conditional load even for full tiles
        // please check first before attempting to load.
        int ITEM = ITEMS_PER_THREAD - 1;
        int idx  = BLOCK_THREADS * ITEM + threadIdx.x;
        if (idx < count1 + count2)
        {
          output[ITEM] = (idx < count1) ? static_cast<T>(input1[idx]) : static_cast<T>(input2[idx - count1]);
        }
      }
      else
      {
#  pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ++ITEM)
        {
          int idx = BLOCK_THREADS * ITEM + threadIdx.x;
          if (idx < count1 + count2)
          {
            output[ITEM] = (idx < count1) ? static_cast<T>(input1[idx]) : static_cast<T>(input2[idx - count1]);
          }
        }
      }
    }

    template <class T, class It>
    THRUST_DEVICE_FUNCTION void reg_to_shared(It output, T (&input)[ITEMS_PER_THREAD])
    {
#  pragma unroll
      for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ++ITEM)
      {
        int idx     = BLOCK_THREADS * ITEM + threadIdx.x;
        output[idx] = input[ITEM];
      }
    }

    template <class OutputIt, class T, class SharedIt>
    void THRUST_DEVICE_FUNCTION scatter(
      OutputIt output,
      T (&input)[ITEMS_PER_THREAD],
      SharedIt shared,
      int active_mask,
      Size thread_output_prefix,
      Size tile_output_prefix,
      int tile_output_count)
    {
      using core::sync_threadblock;

      int local_scatter_idx = thread_output_prefix - tile_output_prefix;
#  pragma unroll
      for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ++ITEM)
      {
        if (active_mask & (1 << ITEM))
        {
          shared[local_scatter_idx++] = input[ITEM];
        }
      }
      sync_threadblock();

      for (int item = threadIdx.x; item < tile_output_count; item += BLOCK_THREADS)
      {
        output[tile_output_prefix + item] = shared[item];
      }
    }

    int THRUST_DEVICE_FUNCTION serial_set_op(
      key_type* keys,
      int keys1_beg,
      int keys2_beg,
      int keys1_count,
      int keys2_count,
      key_type (&output)[ITEMS_PER_THREAD],
      int (&indices)[ITEMS_PER_THREAD],
      CompareOp compare_op,
      SetOp set_op)
    {
      int active_mask = set_op(keys, keys1_beg, keys2_beg, keys1_count, keys2_count, output, indices, compare_op);

      return active_mask;
    }

    //---------------------------------------------------------------------
    // Tile operations
    //---------------------------------------------------------------------

    template <bool IS_LAST_TILE>
    void THRUST_DEVICE_FUNCTION consume_tile(Size tile_idx)
    {
      using core::sync_threadblock;
      using core::uninitialized_array;

      pair<Size, Size> partition_beg = partitions[tile_idx + 0];
      pair<Size, Size> partition_end = partitions[tile_idx + 1];

      Size keys1_beg = partition_beg.first;
      Size keys1_end = partition_end.first;
      Size keys2_beg = partition_beg.second;
      Size keys2_end = partition_end.second;

      // number of keys per tile
      //
      int num_keys1 = static_cast<int>(keys1_end - keys1_beg);
      int num_keys2 = static_cast<int>(keys2_end - keys2_beg);

      // load keys into shared memory for further processing
      key_type keys_loc[ITEMS_PER_THREAD];

      gmem_to_reg<!IS_LAST_TILE>(keys_loc, keys1_in + keys1_beg, keys2_in + keys2_beg, num_keys1, num_keys2);

      reg_to_shared(&storage.load_storage.keys_shared[0], keys_loc);

      sync_threadblock();

      int diag_loc = min<int>(ITEMS_PER_THREAD * threadIdx.x, num_keys1 + num_keys2);

      pair<int, int> partition_loc = balanced_path(
        &storage.load_storage.keys_shared[0],
        &storage.load_storage.keys_shared[num_keys1],
        num_keys1,
        num_keys2,
        diag_loc,
        4,
        compare_op);

      int keys1_beg_loc = partition_loc.first;
      int keys2_beg_loc = partition_loc.second;

      // compute difference between next and current thread
      // to obtain number of elements per thread
      int value = threadIdx.x == 0 ? (num_keys1 << 16) | num_keys2 : (partition_loc.first << 16) | partition_loc.second;

      int dst                          = threadIdx.x == 0 ? BLOCK_THREADS - 1 : threadIdx.x - 1;
      storage.load_storage.offset[dst] = value;

      core::sync_threadblock();

      pair<int, int> partition1_loc = thrust::make_pair(
        storage.load_storage.offset[threadIdx.x] >> 16, storage.load_storage.offset[threadIdx.x] & 0xFFFF);

      int keys1_end_loc = partition1_loc.first;
      int keys2_end_loc = partition1_loc.second;

      int num_keys1_loc = keys1_end_loc - keys1_beg_loc;
      int num_keys2_loc = keys2_end_loc - keys2_beg_loc;

      // perform serial set operation
      //
      int indices[ITEMS_PER_THREAD];

      int active_mask = serial_set_op(
        &storage.load_storage.keys_shared[0],
        keys1_beg_loc,
        keys2_beg_loc + num_keys1,
        num_keys1_loc,
        num_keys2_loc,
        keys_loc,
        indices,
        compare_op,
        set_op);
      sync_threadblock();
#  if 0
        if (ITEMS_PER_THREAD*threadIdx.x >= num_keys1 + num_keys2)
          active_mask = 0;
#  endif

      // look-back scan over thread_output_count
      // to compute global thread_output_base and tile_otput_count;
      Size tile_output_count    = 0;
      Size thread_output_prefix = 0;
      Size tile_output_prefix   = 0;
      Size thread_output_count  = static_cast<Size>(__popc(active_mask));

      if (tile_idx == 0) // first tile
      {
        BlockScan(storage.scan_storage.scan).ExclusiveSum(thread_output_count, thread_output_prefix, tile_output_count);
        if (threadIdx.x == 0)
        {
          // Update tile status if this is not the last tile
          if (!IS_LAST_TILE)
          {
            tile_state.SetInclusive(0, tile_output_count);
          }
        }
      }
      else
      {
        TilePrefixCallback prefix_cb(tile_state, storage.scan_storage.prefix, ::cuda::std::plus<>{}, tile_idx);

        BlockScan(storage.scan_storage.scan).ExclusiveSum(thread_output_count, thread_output_prefix, prefix_cb);
        tile_output_count  = prefix_cb.GetBlockAggregate();
        tile_output_prefix = prefix_cb.GetExclusivePrefix();
      }

      sync_threadblock();

      // scatter results
      //
      scatter(keys_out,
              keys_loc,
              &storage.load_storage.keys_shared[0],
              active_mask,
              thread_output_prefix,
              tile_output_prefix,
              tile_output_count);

      if (HAS_VALUES::value)
      {
        value_type values_loc[ITEMS_PER_THREAD];
        gmem_to_reg<!IS_LAST_TILE>(values_loc, values1_in + keys1_beg, values2_in + keys2_beg, num_keys1, num_keys2);

        sync_threadblock();

        reg_to_shared(&storage.load_storage.values_shared[0], values_loc);

        sync_threadblock();

        // gather items from shared mem
        //
#  pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ++ITEM)
        {
          if (active_mask & (1 << ITEM))
          {
            values_loc[ITEM] = storage.load_storage.values_shared[indices[ITEM]];
          }
        }

        sync_threadblock();

        scatter(values_out,
                values_loc,
                &storage.load_storage.values_shared[0],
                active_mask,
                thread_output_prefix,
                tile_output_prefix,
                tile_output_count);
      }

      if (IS_LAST_TILE && threadIdx.x == 0)
      {
        *output_count = tile_output_prefix + tile_output_count;
      }
    }

    //---------------------------------------------------------------------
    // Constructor
    //---------------------------------------------------------------------

    THRUST_DEVICE_FUNCTION
    impl(TempStorage& storage_,
         ScanTileState& tile_state_,
         KeysIt1 keys1_,
         KeysIt2 keys2_,
         ValuesIt1 values1_,
         ValuesIt2 values2_,
         Size keys1_count_,
         Size keys2_count_,
         KeysOutputIt keys_out_,
         ValuesOutputIt values_out_,
         CompareOp compare_op_,
         SetOp set_op_,
         pair<Size, Size>* partitions_,
         std::size_t* output_count_)
        : storage(storage_)
        , tile_state(tile_state_)
        , keys1_in(core::make_load_iterator(ptx_plan(), keys1_))
        , keys2_in(core::make_load_iterator(ptx_plan(), keys2_))
        , values1_in(core::make_load_iterator(ptx_plan(), values1_))
        , values2_in(core::make_load_iterator(ptx_plan(), values2_))
        , keys1_count(keys1_count_)
        , keys2_count(keys2_count_)
        , keys_out(keys_out_)
        , values_out(values_out_)
        , compare_op(compare_op_)
        , set_op(set_op_)
        , partitions(partitions_)
        , output_count(output_count_)
    {
      int tile_idx  = blockIdx.x;
      int num_tiles = gridDim.x;

      if (tile_idx < num_tiles - 1)
      {
        consume_tile<false>(tile_idx);
      }
      else
      {
        consume_tile<true>(tile_idx);
      }
    }
  }; // struct impl

  //---------------------------------------------------------------------
  // Agent entry point
  //---------------------------------------------------------------------

  THRUST_AGENT_ENTRY(
    KeysIt1 keys1,
    KeysIt2 keys2,
    ValuesIt1 values1,
    ValuesIt2 values2,
    Size keys1_count,
    Size keys2_count,
    KeysOutputIt keys_output,
    ValuesOutputIt values_output,
    CompareOp compare_op,
    SetOp set_op,
    pair<Size, Size>* partitions,
    std::size_t* output_count,
    ScanTileState tile_state,
    char* shmem)
  {
    TempStorage& storage = *reinterpret_cast<TempStorage*>(shmem);

    impl(storage,
         tile_state,
         keys1,
         keys2,
         values1,
         values2,
         keys1_count,
         keys2_count,
         keys_output,
         values_output,
         compare_op,
         set_op,
         partitions,
         output_count);
  }
}; // struct SetOpAgent

template <class KeysIt1, class KeysIt2, class Size, class CompareOp>
struct PartitionAgent
{
  template <class Arch>
  struct PtxPlan : PtxPolicy<256>
  {};

  using ptx_plan = core::specialize_plan<PtxPlan>;

  //---------------------------------------------------------------------
  // Agent entry point
  //---------------------------------------------------------------------

  THRUST_AGENT_ENTRY(
    KeysIt1 keys1,
    KeysIt2 keys2,
    Size keys1_count,
    Size keys2_count,
    Size num_partitions,
    pair<Size, Size>* partitions,
    CompareOp compare_op,
    int items_per_tile,
    char* /*shmem*/)
  {
    Size partition_idx = blockDim.x * blockIdx.x + threadIdx.x;
    if (partition_idx < num_partitions)
    {
      Size partition_at         = min<Size>(partition_idx * items_per_tile, keys1_count + keys2_count);
      pair<Size, Size> diag     = balanced_path(keys1, keys2, keys1_count, keys2_count, partition_at, 4ll, compare_op);
      partitions[partition_idx] = diag;
    }
  }
}; // struct PartitionAgent

template <class ScanTileState, class Size>
struct InitAgent
{
  template <class Arch>
  struct PtxPlan : PtxPolicy<128>
  {};

  using ptx_plan = core::specialize_plan<PtxPlan>;

  //---------------------------------------------------------------------
  // Agent entry point
  //---------------------------------------------------------------------

  THRUST_AGENT_ENTRY(ScanTileState tile_state, Size num_tiles, char* /*shmem*/)
  {
    tile_state.InitializeStatus(num_tiles);
  }
}; // struct InitAgent

//---------------------------------------------------------------------
// Serial set operations
//---------------------------------------------------------------------

// serial_set_intersection
// -----------------------
// emit A if A and B are in range and equal.
struct serial_set_intersection
{
  // max_input_size <= 32
  template <class T, class CompareOp, int ITEMS_PER_THREAD>
  int THRUST_DEVICE_FUNCTION operator()(
    T* keys,
    int keys1_beg,
    int keys2_beg,
    int keys1_count,
    int keys2_count,
    T (&output)[ITEMS_PER_THREAD],
    int (&indices)[ITEMS_PER_THREAD],
    CompareOp compare_op)
  {
    int active_mask = 0;

    int aBegin = keys1_beg;
    int bBegin = keys2_beg;
    int aEnd   = keys1_beg + keys1_count;
    int bEnd   = keys2_beg + keys2_count;

    T aKey = keys[aBegin];
    T bKey = keys[bBegin];

#  pragma unroll
    for (int i = 0; i < ITEMS_PER_THREAD; ++i)
    {
      bool pA = compare_op(aKey, bKey);
      bool pB = compare_op(bKey, aKey);

      // The outputs must come from A by definition of set intersection.
      output[i]  = aKey;
      indices[i] = aBegin;

      if ((aBegin < aEnd) && (bBegin < bEnd) && pA == pB)
      {
        active_mask |= 1 << i;
      }

      if (!pB)
      {
        aKey = keys[++aBegin];
      }
      if (!pA)
      {
        bKey = keys[++bBegin];
      }
    }
    return active_mask;
  }
}; // struct serial_set_intersection

// serial_set_symmetric_difference
// ---------------------
// emit A if A < B and emit B if B < A.
struct serial_set_symmetric_difference
{
  // max_input_size <= 32
  template <class T, class CompareOp, int ITEMS_PER_THREAD>
  int THRUST_DEVICE_FUNCTION operator()(
    T* keys,
    int keys1_beg,
    int keys2_beg,
    int keys1_count,
    int keys2_count,
    T (&output)[ITEMS_PER_THREAD],
    int (&indices)[ITEMS_PER_THREAD],
    CompareOp compare_op)
  {
    int active_mask = 0;

    int aBegin = keys1_beg;
    int bBegin = keys2_beg;
    int aEnd   = keys1_beg + keys1_count;
    int bEnd   = keys2_beg + keys2_count;
    int end    = aEnd + bEnd;

    T aKey = keys[aBegin];
    T bKey = keys[bBegin];

#  pragma unroll
    for (int i = 0; i < ITEMS_PER_THREAD; ++i)
    {
      bool pB = aBegin >= aEnd;
      bool pA = !pB && bBegin >= bEnd;

      if (!pA && !pB)
      {
        pA = compare_op(aKey, bKey);
        pB = !pA && compare_op(bKey, aKey);
      }

      // The outputs must come from A by definition of set difference.
      output[i]  = pA ? aKey : bKey;
      indices[i] = pA ? aBegin : bBegin;

      if (aBegin + bBegin < end && pA != pB)
      {
        active_mask |= 1 << i;
      }

      if (!pB)
      {
        aKey = keys[++aBegin];
      }
      if (!pA)
      {
        bKey = keys[++bBegin];
      }
    }
    return active_mask;
  }
}; // struct set_symmetric_difference

// serial_set_difference
// ---------------------
// emit A if A < B
struct serial_set_difference
{
  // max_input_size <= 32
  template <class T, class CompareOp, int ITEMS_PER_THREAD>
  int THRUST_DEVICE_FUNCTION operator()(
    T* keys,
    int keys1_beg,
    int keys2_beg,
    int keys1_count,
    int keys2_count,
    T (&output)[ITEMS_PER_THREAD],
    int (&indices)[ITEMS_PER_THREAD],
    CompareOp compare_op)
  {
    int active_mask = 0;

    int aBegin = keys1_beg;
    int bBegin = keys2_beg;
    int aEnd   = keys1_beg + keys1_count;
    int bEnd   = keys2_beg + keys2_count;
    int end    = aEnd + bEnd;

    T aKey = keys[aBegin];
    T bKey = keys[bBegin];

#  pragma unroll
    for (int i = 0; i < ITEMS_PER_THREAD; ++i)
    {
      bool pB = aBegin >= aEnd;
      bool pA = !pB && bBegin >= bEnd;

      if (!pA && !pB)
      {
        pA = compare_op(aKey, bKey);
        pB = !pA && compare_op(bKey, aKey);
      }

      // The outputs must come from A by definition of set difference.
      output[i]  = aKey;
      indices[i] = aBegin;

      if (aBegin + bBegin < end && pA)
      {
        active_mask |= 1 << i;
      }

      if (!pB)
      {
        aKey = keys[++aBegin];
      }
      if (!pA)
      {
        bKey = keys[++bBegin];
      }
    }
    return active_mask;
  }
}; // struct set_difference

// serial_set_union
// ----------------
// emit A if A <= B else emit B
struct serial_set_union
{
  // max_input_size <= 32
  template <class T, class CompareOp, int ITEMS_PER_THREAD>
  int THRUST_DEVICE_FUNCTION operator()(
    T* keys,
    int keys1_beg,
    int keys2_beg,
    int keys1_count,
    int keys2_count,
    T (&output)[ITEMS_PER_THREAD],
    int (&indices)[ITEMS_PER_THREAD],
    CompareOp compare_op)
  {
    int active_mask = 0;

    int aBegin = keys1_beg;
    int bBegin = keys2_beg;
    int aEnd   = keys1_beg + keys1_count;
    int bEnd   = keys2_beg + keys2_count;
    int end    = aEnd + bEnd;

    T aKey = keys[aBegin];
    T bKey = keys[bBegin];

#  pragma unroll
    for (int i = 0; i < ITEMS_PER_THREAD; ++i)
    {
      bool pB = aBegin >= aEnd;
      bool pA = !pB && bBegin >= bEnd;

      if (!pA && !pB)
      {
        pA = compare_op(aKey, bKey);
        pB = !pA && compare_op(bKey, aKey);
      }

      // Output A in case of a tie, so check if b < a.
      output[i]  = pB ? bKey : aKey;
      indices[i] = pB ? bBegin : aBegin;

      if (aBegin + bBegin < end)
      {
        active_mask |= 1 << i;
      }

      if (!pB)
      {
        aKey = keys[++aBegin];
      }
      if (!pA)
      {
        bKey = keys[++bBegin];
      }
    }
    return active_mask;
  }
}; // struct set_union

template <class HAS_VALUES,
          class KeysIt1,
          class KeysIt2,
          class ValuesIt1,
          class ValuesIt2,
          class Size,
          class KeysOutputIt,
          class ValuesOutputIt,
          class CompareOp,
          class SetOp>
cudaError_t THRUST_RUNTIME_FUNCTION doit_step(
  void* d_temp_storage,
  size_t& temp_storage_size,
  KeysIt1 keys1,
  KeysIt2 keys2,
  ValuesIt1 values1,
  ValuesIt2 values2,
  Size num_keys1,
  Size num_keys2,
  KeysOutputIt keys_output,
  ValuesOutputIt values_output,
  std::size_t* output_count,
  CompareOp compare_op,
  SetOp set_op,
  cudaStream_t stream)
{
  Size keys_total = num_keys1 + num_keys2;
  if (keys_total == 0)
  {
    return cudaErrorNotSupported;
  }

  cudaError_t status = cudaSuccess;

  using core::AgentLauncher;
  using core::AgentPlan;

  using set_op_agent = AgentLauncher<
    SetOpAgent<KeysIt1, KeysIt2, ValuesIt1, ValuesIt2, KeysOutputIt, ValuesOutputIt, Size, CompareOp, SetOp, HAS_VALUES>>;

  using partition_agent = AgentLauncher<PartitionAgent<KeysIt1, KeysIt2, Size, CompareOp>>;

  using ScanTileState = typename set_op_agent::ScanTileState;
  using init_agent    = AgentLauncher<InitAgent<ScanTileState, Size>>;

  AgentPlan set_op_plan    = set_op_agent::get_plan(stream);
  AgentPlan init_plan      = init_agent::get_plan();
  AgentPlan partition_plan = partition_agent::get_plan();

  int tile_size  = set_op_plan.items_per_tile;
  Size num_tiles = (keys_total + tile_size - 1) / tile_size;

  size_t tile_agent_storage;
  status = ScanTileState::AllocationSize(static_cast<int>(num_tiles), tile_agent_storage);
  CUDA_CUB_RET_IF_FAIL(status);

  size_t vshmem_storage          = core::vshmem_size(set_op_plan.shared_memory_size, num_tiles);
  size_t partition_agent_storage = (num_tiles + 1) * sizeof(Size) * 2;

  void* allocations[3]       = {nullptr, nullptr, nullptr};
  size_t allocation_sizes[3] = {tile_agent_storage, partition_agent_storage, vshmem_storage};

  status = core::alias_storage(d_temp_storage, temp_storage_size, allocations, allocation_sizes);
  CUDA_CUB_RET_IF_FAIL(status);

  if (d_temp_storage == nullptr)
  {
    return status;
  }

  ScanTileState tile_state;
  status = tile_state.Init(static_cast<int>(num_tiles), allocations[0], allocation_sizes[0]);
  CUDA_CUB_RET_IF_FAIL(status);

  pair<Size, Size>* partitions = (pair<Size, Size>*) allocations[1];
  char* vshmem_ptr             = vshmem_storage > 0 ? (char*) allocations[2] : nullptr;

  init_agent ia(init_plan, num_tiles, stream, "set_op::init_agent");
  ia.launch(tile_state, num_tiles);
  CUDA_CUB_RET_IF_FAIL(cudaPeekAtLastError());

  partition_agent pa(partition_plan, num_tiles + 1, stream, "set_op::partition agent");
  pa.launch(keys1, keys2, num_keys1, num_keys2, num_tiles + 1, partitions, compare_op, tile_size);
  CUDA_CUB_RET_IF_FAIL(cudaPeekAtLastError());

  set_op_agent sa(set_op_plan, keys_total, stream, vshmem_ptr, "set_op::set_op_agent");
  sa.launch(
    keys1,
    keys2,
    values1,
    values2,
    num_keys1,
    num_keys2,
    keys_output,
    values_output,
    compare_op,
    set_op,
    partitions,
    output_count,
    tile_state);
  CUDA_CUB_RET_IF_FAIL(cudaPeekAtLastError());

  return status;
}

template <typename HAS_VALUES,
          typename Derived,
          typename KeysIt1,
          typename KeysIt2,
          typename ValuesIt1,
          typename ValuesIt2,
          typename KeysOutputIt,
          typename ValuesOutputIt,
          typename CompareOp,
          typename SetOp>
THRUST_RUNTIME_FUNCTION pair<KeysOutputIt, ValuesOutputIt> set_operations(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ValuesIt1 values1_first,
  ValuesIt2 values2_first,
  KeysOutputIt keys_output,
  ValuesOutputIt values_output,
  CompareOp compare_op,
  SetOp set_op)
{
  using size_type = typename iterator_traits<KeysIt1>::difference_type;

  size_type num_keys1 = static_cast<size_type>(thrust::distance(keys1_first, keys1_last));
  size_type num_keys2 = static_cast<size_type>(thrust::distance(keys2_first, keys2_last));

  if (num_keys1 + num_keys2 == 0)
  {
    return thrust::make_pair(keys_output, values_output);
  }

  size_t temp_storage_bytes = 0;
  cudaStream_t stream       = cuda_cub::stream(policy);

  cudaError_t status;
  THRUST_DOUBLE_INDEX_TYPE_DISPATCH(
    status,
    doit_step<HAS_VALUES>,
    num_keys1,
    num_keys2,
    (nullptr,
     temp_storage_bytes,
     keys1_first,
     keys2_first,
     values1_first,
     values2_first,
     num_keys1_fixed,
     num_keys2_fixed,
     keys_output,
     values_output,
     static_cast<std::size_t*>(nullptr),
     compare_op,
     set_op,
     stream));
  cuda_cub::throw_on_error(status, "set_operations failed on 1st step");

  size_t allocation_sizes[2] = {sizeof(std::size_t), temp_storage_bytes};
  void* allocations[2]       = {nullptr, nullptr};

  size_t storage_size = 0;

  status = core::alias_storage(nullptr, storage_size, allocations, allocation_sizes);
  cuda_cub::throw_on_error(status, "set_operations failed on 1st alias_storage");

  // Allocate temporary storage.
  thrust::detail::temporary_array<std::uint8_t, Derived> tmp(policy, storage_size);
  void* ptr = static_cast<void*>(tmp.data().get());

  status = core::alias_storage(ptr, storage_size, allocations, allocation_sizes);
  cuda_cub::throw_on_error(status, "set_operations failed on 2nd alias_storage");

  std::size_t* d_output_count = thrust::detail::aligned_reinterpret_cast<std::size_t*>(allocations[0]);

  THRUST_DOUBLE_INDEX_TYPE_DISPATCH(
    status,
    doit_step<HAS_VALUES>,
    num_keys1,
    num_keys2,
    (allocations[1],
     temp_storage_bytes,
     keys1_first,
     keys2_first,
     values1_first,
     values2_first,
     num_keys1_fixed,
     num_keys2_fixed,
     keys_output,
     values_output,
     d_output_count,
     compare_op,
     set_op,
     stream));
  cuda_cub::throw_on_error(status, "set_operations failed on 2nd step");

  status = cuda_cub::synchronize(policy);
  cuda_cub::throw_on_error(status, "set_operations failed to synchronize");

  std::size_t output_count = cuda_cub::get_value(policy, d_output_count);

  return thrust::make_pair(keys_output + output_count, values_output + output_count);
}
} // namespace __set_operations

//-------------------------
// Thrust API entry points
//-------------------------

_CCCL_EXEC_CHECK_DISABLE
template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt, class CompareOp>
OutputIt _CCCL_HOST_DEVICE set_difference(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result,
  CompareOp compare)
{
  THRUST_CDP_DISPATCH(
    (using items1_t = thrust::iterator_value_t<ItemsIt1>; items1_t* null_ = nullptr;
     auto tmp = __set_operations::set_operations<thrust::detail::false_type>(
       policy,
       items1_first,
       items1_last,
       items2_first,
       items2_last,
       null_,
       null_,
       result,
       null_,
       compare,
       __set_operations::serial_set_difference());
     result = tmp.first;),
    (result = thrust::set_difference(
       cvt_to_seq(derived_cast(policy)), items1_first, items1_last, items2_first, items2_last, result, compare);));
  return result;
}

template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt>
OutputIt _CCCL_HOST_DEVICE set_difference(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result)
{
  using value_type = typename thrust::iterator_value<ItemsIt1>::type;
  return cuda_cub::set_difference(
    policy, items1_first, items1_last, items2_first, items2_last, result, less<value_type>());
}

/*****************************/

_CCCL_EXEC_CHECK_DISABLE
template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt, class CompareOp>
OutputIt _CCCL_HOST_DEVICE set_intersection(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result,
  CompareOp compare)
{
  THRUST_CDP_DISPATCH(
    (using items1_t = thrust::iterator_value_t<ItemsIt1>; items1_t* null_ = nullptr;
     auto tmp = __set_operations::set_operations<thrust::detail::false_type>(
       policy,
       items1_first,
       items1_last,
       items2_first,
       items2_last,
       null_,
       null_,
       result,
       null_,
       compare,
       __set_operations::serial_set_intersection());
     result = tmp.first;),
    (result = thrust::set_intersection(
       cvt_to_seq(derived_cast(policy)), items1_first, items1_last, items2_first, items2_last, result, compare);));
  return result;
}

template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt>
OutputIt _CCCL_HOST_DEVICE set_intersection(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result)
{
  using value_type = typename thrust::iterator_value<ItemsIt1>::type;
  return cuda_cub::set_intersection(
    policy, items1_first, items1_last, items2_first, items2_last, result, less<value_type>());
}

/*****************************/

_CCCL_EXEC_CHECK_DISABLE
template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt, class CompareOp>
OutputIt _CCCL_HOST_DEVICE set_symmetric_difference(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result,
  CompareOp compare)
{
  THRUST_CDP_DISPATCH(
    (using items1_t = thrust::iterator_value_t<ItemsIt1>; items1_t* null_ = nullptr;
     auto tmp = __set_operations::set_operations<thrust::detail::false_type>(
       policy,
       items1_first,
       items1_last,
       items2_first,
       items2_last,
       null_,
       null_,
       result,
       null_,
       compare,
       __set_operations::serial_set_symmetric_difference());
     result = tmp.first;),
    (result = thrust::set_symmetric_difference(
       cvt_to_seq(derived_cast(policy)), items1_first, items1_last, items2_first, items2_last, result, compare);));
  return result;
}

template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt>
OutputIt _CCCL_HOST_DEVICE set_symmetric_difference(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result)
{
  using value_type = typename thrust::iterator_value<ItemsIt1>::type;
  return cuda_cub::set_symmetric_difference(
    policy, items1_first, items1_last, items2_first, items2_last, result, less<value_type>());
}

/*****************************/

_CCCL_EXEC_CHECK_DISABLE
template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt, class CompareOp>
OutputIt _CCCL_HOST_DEVICE set_union(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result,
  CompareOp compare)
{
  THRUST_CDP_DISPATCH(
    (using items1_t = thrust::iterator_value_t<ItemsIt1>; items1_t* null_ = nullptr;
     auto tmp = __set_operations::set_operations<thrust::detail::false_type>(
       policy,
       items1_first,
       items1_last,
       items2_first,
       items2_last,
       null_,
       null_,
       result,
       null_,
       compare,
       __set_operations::serial_set_union());
     result = tmp.first;),
    (result = thrust::set_union(
       cvt_to_seq(derived_cast(policy)), items1_first, items1_last, items2_first, items2_last, result, compare);));
  return result;
}

template <class Derived, class ItemsIt1, class ItemsIt2, class OutputIt>
OutputIt _CCCL_HOST_DEVICE set_union(
  execution_policy<Derived>& policy,
  ItemsIt1 items1_first,
  ItemsIt1 items1_last,
  ItemsIt2 items2_first,
  ItemsIt2 items2_last,
  OutputIt result)
{
  using value_type = typename thrust::iterator_value<ItemsIt1>::type;
  return cuda_cub::set_union(policy, items1_first, items1_last, items2_first, items2_last, result, less<value_type>());
}

/*****************************/
/*****************************/
/*****     *_by_key      *****/
/*****************************/
/*****************************/

/*****************************/

_CCCL_EXEC_CHECK_DISABLE
template <class Derived,
          class KeysIt1,
          class KeysIt2,
          class ItemsIt1,
          class ItemsIt2,
          class KeysOutputIt,
          class ItemsOutputIt,
          class CompareOp>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_difference_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  ItemsIt2 items2_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result,
  CompareOp compare_op)
{
  auto ret = thrust::make_pair(keys_result, items_result);
  THRUST_CDP_DISPATCH(
    (ret = __set_operations::set_operations<thrust::detail::true_type>(
       policy,
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       items2_first,
       keys_result,
       items_result,
       compare_op,
       __set_operations::serial_set_difference());),
    (ret = thrust::set_difference_by_key(
       cvt_to_seq(derived_cast(policy)),
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       items2_first,
       keys_result,
       items_result,
       compare_op);));
  return ret;
}

template <class Derived, class KeysIt1, class KeysIt2, class ItemsIt1, class ItemsIt2, class KeysOutputIt, class ItemsOutputIt>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_difference_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  ItemsIt2 items2_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result)
{
  using value_type = typename thrust::iterator_value<KeysIt1>::type;
  return cuda_cub::set_difference_by_key(
    policy,
    keys1_first,
    keys1_last,
    keys2_first,
    keys2_last,
    items1_first,
    items2_first,
    keys_result,
    items_result,
    less<value_type>());
}

/*****************************/

_CCCL_EXEC_CHECK_DISABLE
template <class Derived,
          class KeysIt1,
          class KeysIt2,
          class ItemsIt1,
          class ItemsIt2,
          class KeysOutputIt,
          class ItemsOutputIt,
          class CompareOp>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_intersection_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result,
  CompareOp compare_op)
{
  auto ret = thrust::make_pair(keys_result, items_result);
  THRUST_CDP_DISPATCH(
    (ret = __set_operations::set_operations<thrust::detail::true_type>(
       policy,
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       items1_first,
       keys_result,
       items_result,
       compare_op,
       __set_operations::serial_set_intersection());),
    (ret = thrust::set_intersection_by_key(
       cvt_to_seq(derived_cast(policy)),
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       keys_result,
       items_result,
       compare_op);));
  return ret;
}

template <class Derived, class KeysIt1, class KeysIt2, class ItemsIt1, class ItemsIt2, class KeysOutputIt, class ItemsOutputIt>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_intersection_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result)
{
  using value_type = typename thrust::iterator_value<KeysIt1>::type;
  return cuda_cub::set_intersection_by_key(
    policy,
    keys1_first,
    keys1_last,
    keys2_first,
    keys2_last,
    items1_first,
    keys_result,
    items_result,
    less<value_type>());
}

/*****************************/

_CCCL_EXEC_CHECK_DISABLE
template <class Derived,
          class KeysIt1,
          class KeysIt2,
          class ItemsIt1,
          class ItemsIt2,
          class KeysOutputIt,
          class ItemsOutputIt,
          class CompareOp>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_symmetric_difference_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  ItemsIt2 items2_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result,
  CompareOp compare_op)
{
  auto ret = thrust::make_pair(keys_result, items_result);
  THRUST_CDP_DISPATCH(
    (ret = __set_operations::set_operations<thrust::detail::true_type>(
       policy,
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       items2_first,
       keys_result,
       items_result,
       compare_op,
       __set_operations::serial_set_symmetric_difference());),
    (ret = thrust::set_symmetric_difference_by_key(
       cvt_to_seq(derived_cast(policy)),
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       items2_first,
       keys_result,
       items_result,
       compare_op);));
  return ret;
}

template <class Derived, class KeysIt1, class KeysIt2, class ItemsIt1, class ItemsIt2, class KeysOutputIt, class ItemsOutputIt>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_symmetric_difference_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  ItemsIt2 items2_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result)
{
  using value_type = typename thrust::iterator_value<KeysIt1>::type;
  return cuda_cub::set_symmetric_difference_by_key(
    policy,
    keys1_first,
    keys1_last,
    keys2_first,
    keys2_last,
    items1_first,
    items2_first,
    keys_result,
    items_result,
    less<value_type>());
}

/*****************************/

_CCCL_EXEC_CHECK_DISABLE
template <class Derived,
          class KeysIt1,
          class KeysIt2,
          class ItemsIt1,
          class ItemsIt2,
          class KeysOutputIt,
          class ItemsOutputIt,
          class CompareOp>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_union_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  ItemsIt2 items2_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result,
  CompareOp compare_op)
{
  auto ret = thrust::make_pair(keys_result, items_result);
  THRUST_CDP_DISPATCH(
    (ret = __set_operations::set_operations<thrust::detail::true_type>(
       policy,
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       items2_first,
       keys_result,
       items_result,
       compare_op,
       __set_operations::serial_set_union());),
    (ret = thrust::set_union_by_key(
       cvt_to_seq(derived_cast(policy)),
       keys1_first,
       keys1_last,
       keys2_first,
       keys2_last,
       items1_first,
       items2_first,
       keys_result,
       items_result,
       compare_op);));
  return ret;
}

template <class Derived, class KeysIt1, class KeysIt2, class ItemsIt1, class ItemsIt2, class KeysOutputIt, class ItemsOutputIt>
pair<KeysOutputIt, ItemsOutputIt> _CCCL_HOST_DEVICE set_union_by_key(
  execution_policy<Derived>& policy,
  KeysIt1 keys1_first,
  KeysIt1 keys1_last,
  KeysIt2 keys2_first,
  KeysIt2 keys2_last,
  ItemsIt1 items1_first,
  ItemsIt2 items2_first,
  KeysOutputIt keys_result,
  ItemsOutputIt items_result)
{
  using value_type = typename thrust::iterator_value<KeysIt1>::type;
  return cuda_cub::set_union_by_key(
    policy,
    keys1_first,
    keys1_last,
    keys2_first,
    keys2_last,
    items1_first,
    items2_first,
    keys_result,
    items_result,
    less<value_type>());
}

} // namespace cuda_cub
THRUST_NAMESPACE_END
#endif
