thrust/cub/block/block_exchange.cuh

/******************************************************************************
 * Copyright (c) 2011, Duane Merrill.  All rights reserved.
 * Copyright (c) 2011-2018, 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;
 * 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.
 *
 ******************************************************************************/

/**
 * \file
 * The cub::BlockExchange class provides [<em>collective</em>](index.html#sec0) methods for rearranging data partitioned across a CUDA thread block.
 */

#pragma once

#include "../config.cuh"
#include "../util_ptx.cuh"
#include "../util_type.cuh"

/// Optional outer namespace(s)
CUB_NS_PREFIX

/// CUB namespace
namespace cub {

/**
 * \brief The BlockExchange class provides [<em>collective</em>](index.html#sec0) methods for rearranging data partitioned across a CUDA thread block. ![](transpose_logo.png)
 * \ingroup BlockModule
 *
 * \tparam T                    The data type to be exchanged.
 * \tparam BLOCK_DIM_X          The thread block length in threads along the X dimension
 * \tparam ITEMS_PER_THREAD     The number of items partitioned onto each thread.
 * \tparam WARP_TIME_SLICING    <b>[optional]</b> When \p true, only use enough shared memory for a single warp's worth of tile data, time-slicing the block-wide exchange over multiple synchronized rounds.  Yields a smaller memory footprint at the expense of decreased parallelism.  (Default: false)
 * \tparam BLOCK_DIM_Y          <b>[optional]</b> The thread block length in threads along the Y dimension (default: 1)
 * \tparam BLOCK_DIM_Z          <b>[optional]</b> The thread block length in threads along the Z dimension (default: 1)
 * \tparam PTX_ARCH             <b>[optional]</b> \ptxversion
 *
 * \par Overview
 * - It is commonplace for blocks of threads to rearrange data items between
 *   threads.  For example, the device-accessible memory subsystem prefers access patterns
 *   where data items are "striped" across threads (where consecutive threads access consecutive items),
 *   yet most block-wide operations prefer a "blocked" partitioning of items across threads
 *   (where consecutive items belong to a single thread).
 * - BlockExchange supports the following types of data exchanges:
 *   - Transposing between [<em>blocked</em>](index.html#sec5sec3) and [<em>striped</em>](index.html#sec5sec3) arrangements
 *   - Transposing between [<em>blocked</em>](index.html#sec5sec3) and [<em>warp-striped</em>](index.html#sec5sec3) arrangements
 *   - Scattering ranked items to a [<em>blocked arrangement</em>](index.html#sec5sec3)
 *   - Scattering ranked items to a [<em>striped arrangement</em>](index.html#sec5sec3)
 * - \rowmajor
 *
 * \par A Simple Example
 * \blockcollective{BlockExchange}
 * \par
 * The code snippet below illustrates the conversion from a "blocked" to a "striped" arrangement
 * of 512 integer items partitioned across 128 threads where each thread owns 4 items.
 * \par
 * \code
 * #include <cub/cub.cuh>   // or equivalently <cub/block/block_exchange.cuh>
 *
 * __global__ void ExampleKernel(int *d_data, ...)
 * {
 *     // Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each
 *     typedef cub::BlockExchange<int, 128, 4> BlockExchange;
 *
 *     // Allocate shared memory for BlockExchange
 *     __shared__ typename BlockExchange::TempStorage temp_storage;
 *
 *     // Load a tile of data striped across threads
 *     int thread_data[4];
 *     cub::LoadDirectStriped<128>(threadIdx.x, d_data, thread_data);
 *
 *     // Collectively exchange data into a blocked arrangement across threads
 *     BlockExchange(temp_storage).StripedToBlocked(thread_data);
 *
 * \endcode
 * \par
 * Suppose the set of striped input \p thread_data across the block of threads is
 * <tt>{ [0,128,256,384], [1,129,257,385], ..., [127,255,383,511] }</tt>.
 * The corresponding output \p thread_data in those threads will be
 * <tt>{ [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }</tt>.
 *
 * \par Performance Considerations
 * - Proper device-specific padding ensures zero bank conflicts for most types.
 *
 */
template <
    typename    InputT,
    int         BLOCK_DIM_X,
    int         ITEMS_PER_THREAD,
    bool        WARP_TIME_SLICING   = false,
    int         BLOCK_DIM_Y         = 1,
    int         BLOCK_DIM_Z         = 1,
    int         PTX_ARCH            = CUB_PTX_ARCH>
class BlockExchange
{
private:

    /******************************************************************************
     * Constants
     ******************************************************************************/

    /// Constants
    enum
    {
        /// The thread block size in threads
        BLOCK_THREADS               = BLOCK_DIM_X * BLOCK_DIM_Y * BLOCK_DIM_Z,

        LOG_WARP_THREADS            = CUB_LOG_WARP_THREADS(PTX_ARCH),
        WARP_THREADS                = 1 << LOG_WARP_THREADS,
        WARPS                       = (BLOCK_THREADS + WARP_THREADS - 1) / WARP_THREADS,

        LOG_SMEM_BANKS              = CUB_LOG_SMEM_BANKS(PTX_ARCH),
        SMEM_BANKS                  = 1 << LOG_SMEM_BANKS,

        TILE_ITEMS                  = BLOCK_THREADS * ITEMS_PER_THREAD,

        TIME_SLICES                 = (WARP_TIME_SLICING) ? WARPS : 1,

        TIME_SLICED_THREADS         = (WARP_TIME_SLICING) ? CUB_MIN(BLOCK_THREADS, WARP_THREADS) : BLOCK_THREADS,
        TIME_SLICED_ITEMS           = TIME_SLICED_THREADS * ITEMS_PER_THREAD,

        WARP_TIME_SLICED_THREADS    = CUB_MIN(BLOCK_THREADS, WARP_THREADS),
        WARP_TIME_SLICED_ITEMS      = WARP_TIME_SLICED_THREADS * ITEMS_PER_THREAD,

        // Insert padding to avoid bank conflicts during raking when items per thread is a power of two and > 4 (otherwise we can typically use 128b loads)
        INSERT_PADDING              = (ITEMS_PER_THREAD > 4) && (PowerOfTwo<ITEMS_PER_THREAD>::VALUE),
        PADDING_ITEMS               = (INSERT_PADDING) ? (TIME_SLICED_ITEMS >> LOG_SMEM_BANKS) : 0,
    };

    /******************************************************************************
     * Type definitions
     ******************************************************************************/

    /// Shared memory storage layout type
    struct __align__(16) _TempStorage
    {
        InputT buff[TIME_SLICED_ITEMS + PADDING_ITEMS];
    };

public:

    /// \smemstorage{BlockExchange}
    struct TempStorage : Uninitialized<_TempStorage> {};

private:


    /******************************************************************************
     * Thread fields
     ******************************************************************************/

    /// Shared storage reference
    _TempStorage &temp_storage;

    /// Linear thread-id
    unsigned int linear_tid;
    unsigned int lane_id;
    unsigned int warp_id;
    unsigned int warp_offset;


    /******************************************************************************
     * Utility methods
     ******************************************************************************/

    /// Internal storage allocator
    __device__ __forceinline__ _TempStorage& PrivateStorage()
    {
        __shared__ _TempStorage private_storage;
        return private_storage;
    }


    /**
     * Transposes data items from <em>blocked</em> arrangement to <em>striped</em> arrangement.  Specialized for no timeslicing.
     */
    template <typename OutputT>
    __device__ __forceinline__ void BlockedToStriped(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<false> /*time_slicing*/)
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = (linear_tid * ITEMS_PER_THREAD) + ITEM;
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            temp_storage.buff[item_offset] = input_items[ITEM];
        }

        CTA_SYNC();

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = int(ITEM * BLOCK_THREADS) + linear_tid;
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            output_items[ITEM] = temp_storage.buff[item_offset];
        }
    }


    /**
     * Transposes data items from <em>blocked</em> arrangement to <em>striped</em> arrangement.  Specialized for warp-timeslicing.
     */
    template <typename OutputT>
    __device__ __forceinline__ void BlockedToStriped(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<true>  /*time_slicing*/)
    {
        InputT temp_items[ITEMS_PER_THREAD];

        #pragma unroll
        for (int SLICE = 0; SLICE < TIME_SLICES; SLICE++)
        {
            const int SLICE_OFFSET  = SLICE * TIME_SLICED_ITEMS;
            const int SLICE_OOB     = SLICE_OFFSET + TIME_SLICED_ITEMS;

            CTA_SYNC();

            if (warp_id == SLICE)
            {
                #pragma unroll
                for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
                {
                    int item_offset = (lane_id * ITEMS_PER_THREAD) + ITEM;
                    if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                    temp_storage.buff[item_offset] = input_items[ITEM];
                }
            }

            CTA_SYNC();

            #pragma unroll
            for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
            {
                // Read a strip of items
                const int STRIP_OFFSET  = ITEM * BLOCK_THREADS;
                const int STRIP_OOB     = STRIP_OFFSET + BLOCK_THREADS;

                if ((SLICE_OFFSET < STRIP_OOB) && (SLICE_OOB > STRIP_OFFSET))
                {
                    int item_offset = STRIP_OFFSET + linear_tid - SLICE_OFFSET;
                    if ((item_offset >= 0) && (item_offset < TIME_SLICED_ITEMS))
                    {
                        if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                        temp_items[ITEM] = temp_storage.buff[item_offset];
                    }
                }
            }
        }

        // Copy
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            output_items[ITEM] = temp_items[ITEM];
        }
    }


    /**
     * Transposes data items from <em>blocked</em> arrangement to <em>warp-striped</em> arrangement. Specialized for no timeslicing
     */
    template <typename OutputT>
    __device__ __forceinline__ void BlockedToWarpStriped(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<false> /*time_slicing*/)
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = warp_offset + ITEM + (lane_id * ITEMS_PER_THREAD);
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            temp_storage.buff[item_offset] = input_items[ITEM];
        }

        WARP_SYNC(0xffffffff);

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = warp_offset + (ITEM * WARP_TIME_SLICED_THREADS) + lane_id;
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            output_items[ITEM] = temp_storage.buff[item_offset];
        }
    }

    /**
     * Transposes data items from <em>blocked</em> arrangement to <em>warp-striped</em> arrangement. Specialized for warp-timeslicing
     */
    template <typename OutputT>
    __device__ __forceinline__ void BlockedToWarpStriped(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<true>  /*time_slicing*/)
    {
        if (warp_id == 0)
        {
            #pragma unroll
            for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
            {
                int item_offset = ITEM + (lane_id * ITEMS_PER_THREAD);
                if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                temp_storage.buff[item_offset] = input_items[ITEM];
            }

            WARP_SYNC(0xffffffff);

            #pragma unroll
            for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
            {
                int item_offset = (ITEM * WARP_TIME_SLICED_THREADS) + lane_id;
                if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                output_items[ITEM] = temp_storage.buff[item_offset];
            }
        }

        #pragma unroll
        for (unsigned int SLICE = 1; SLICE < TIME_SLICES; ++SLICE)
        {
            CTA_SYNC();

            if (warp_id == SLICE)
            {
                #pragma unroll
                for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
                {
                    int item_offset = ITEM + (lane_id * ITEMS_PER_THREAD);
                    if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                    temp_storage.buff[item_offset] = input_items[ITEM];
                }

                WARP_SYNC(0xffffffff);

                #pragma unroll
                for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
                {
                    int item_offset = (ITEM * WARP_TIME_SLICED_THREADS) + lane_id;
                    if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                    output_items[ITEM] = temp_storage.buff[item_offset];
                }
            }
        }
    }


    /**
     * Transposes data items from <em>striped</em> arrangement to <em>blocked</em> arrangement.  Specialized for no timeslicing.
     */
    template <typename OutputT>
    __device__ __forceinline__ void StripedToBlocked(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<false> /*time_slicing*/)
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = int(ITEM * BLOCK_THREADS) + linear_tid;
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            temp_storage.buff[item_offset] = input_items[ITEM];
        }

        CTA_SYNC();

        // No timeslicing
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = (linear_tid * ITEMS_PER_THREAD) + ITEM;
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            output_items[ITEM] = temp_storage.buff[item_offset];
        }
    }


    /**
     * Transposes data items from <em>striped</em> arrangement to <em>blocked</em> arrangement.  Specialized for warp-timeslicing.
     */
    template <typename OutputT>
    __device__ __forceinline__ void StripedToBlocked(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<true>  /*time_slicing*/)
    {
        // Warp time-slicing
        InputT temp_items[ITEMS_PER_THREAD];

        #pragma unroll
        for (int SLICE = 0; SLICE < TIME_SLICES; SLICE++)
        {
            const int SLICE_OFFSET  = SLICE * TIME_SLICED_ITEMS;
            const int SLICE_OOB     = SLICE_OFFSET + TIME_SLICED_ITEMS;

            CTA_SYNC();

            #pragma unroll
            for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
            {
                // Write a strip of items
                const int STRIP_OFFSET  = ITEM * BLOCK_THREADS;
                const int STRIP_OOB     = STRIP_OFFSET + BLOCK_THREADS;

                if ((SLICE_OFFSET < STRIP_OOB) && (SLICE_OOB > STRIP_OFFSET))
                {
                    int item_offset = STRIP_OFFSET + linear_tid - SLICE_OFFSET;
                    if ((item_offset >= 0) && (item_offset < TIME_SLICED_ITEMS))
                    {
                        if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                        temp_storage.buff[item_offset] = input_items[ITEM];
                    }
                }
            }

            CTA_SYNC();

            if (warp_id == SLICE)
            {
                #pragma unroll
                for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
                {
                    int item_offset = (lane_id * ITEMS_PER_THREAD) + ITEM;
                    if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                    temp_items[ITEM] = temp_storage.buff[item_offset];
                }
            }
        }

        // Copy
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            output_items[ITEM] = temp_items[ITEM];
        }
    }


    /**
     * Transposes data items from <em>warp-striped</em> arrangement to <em>blocked</em> arrangement.  Specialized for no timeslicing
     */
    template <typename OutputT>
    __device__ __forceinline__ void WarpStripedToBlocked(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<false> /*time_slicing*/)
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = warp_offset + (ITEM * WARP_TIME_SLICED_THREADS) + lane_id;
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            new (&temp_storage.buff[item_offset]) InputT (input_items[ITEM]);
        }

        WARP_SYNC(0xffffffff);

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = warp_offset + ITEM + (lane_id * ITEMS_PER_THREAD);
            if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
            new(&output_items[ITEM]) OutputT(temp_storage.buff[item_offset]);
        }
    }


    /**
     * Transposes data items from <em>warp-striped</em> arrangement to <em>blocked</em> arrangement.  Specialized for warp-timeslicing
     */
    template <typename OutputT>
    __device__ __forceinline__ void WarpStripedToBlocked(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        Int2Type<true>  /*time_slicing*/)
    {
        #pragma unroll
        for (unsigned int SLICE = 0; SLICE < TIME_SLICES; ++SLICE)
        {
            CTA_SYNC();

            if (warp_id == SLICE)
            {
                #pragma unroll
                for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
                {
                    int item_offset = (ITEM * WARP_TIME_SLICED_THREADS) + lane_id;
                    if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                    temp_storage.buff[item_offset] = input_items[ITEM];
                }

                WARP_SYNC(0xffffffff);

                #pragma unroll
                for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
                {
                    int item_offset = ITEM + (lane_id * ITEMS_PER_THREAD);
                    if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                    output_items[ITEM] = temp_storage.buff[item_offset];
                }
            }
        }
    }


    /**
     * Exchanges data items annotated by rank into <em>blocked</em> arrangement.  Specialized for no timeslicing.
     */
    template <typename OutputT, typename OffsetT>
    __device__ __forceinline__ void ScatterToBlocked(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OffsetT         ranks[ITEMS_PER_THREAD],    ///< [in] Corresponding scatter ranks
        Int2Type<false> /*time_slicing*/)
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = ranks[ITEM];
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            temp_storage.buff[item_offset] = input_items[ITEM];
        }

        CTA_SYNC();

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = (linear_tid * ITEMS_PER_THREAD) + ITEM;
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            output_items[ITEM] = temp_storage.buff[item_offset];
        }
    }

    /**
     * Exchanges data items annotated by rank into <em>blocked</em> arrangement.  Specialized for warp-timeslicing.
     */
    template <typename OutputT, typename OffsetT>
    __device__ __forceinline__ void ScatterToBlocked(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OffsetT         ranks[ITEMS_PER_THREAD],    ///< [in] Corresponding scatter ranks
        Int2Type<true>  /*time_slicing*/)
    {
        InputT temp_items[ITEMS_PER_THREAD];

        #pragma unroll
        for (int SLICE = 0; SLICE < TIME_SLICES; SLICE++)
        {
            CTA_SYNC();

            const int SLICE_OFFSET = TIME_SLICED_ITEMS * SLICE;

            #pragma unroll
            for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
            {
                int item_offset = ranks[ITEM] - SLICE_OFFSET;
                if ((item_offset >= 0) && (item_offset < WARP_TIME_SLICED_ITEMS))
                {
                    if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
                    temp_storage.buff[item_offset] = input_items[ITEM];
                }
            }

            CTA_SYNC();

            if (warp_id == SLICE)
            {
                #pragma unroll
                for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
                {
                    int item_offset = (lane_id * ITEMS_PER_THREAD) + ITEM;
                    if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
                    temp_items[ITEM] = temp_storage.buff[item_offset];
                }
            }
        }

        // Copy
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            output_items[ITEM] = temp_items[ITEM];
        }
    }


    /**
     * Exchanges data items annotated by rank into <em>striped</em> arrangement.  Specialized for no timeslicing.
     */
    template <typename OutputT, typename OffsetT>
    __device__ __forceinline__ void ScatterToStriped(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OffsetT         ranks[ITEMS_PER_THREAD],    ///< [in] Corresponding scatter ranks
        Int2Type<false> /*time_slicing*/)
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = ranks[ITEM];
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            temp_storage.buff[item_offset] = input_items[ITEM];
        }

        CTA_SYNC();

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = int(ITEM * BLOCK_THREADS) + linear_tid;
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            output_items[ITEM] = temp_storage.buff[item_offset];
        }
    }


    /**
     * Exchanges data items annotated by rank into <em>striped</em> arrangement.  Specialized for warp-timeslicing.
     */
    template <typename OutputT, typename OffsetT>
    __device__ __forceinline__ void ScatterToStriped(
        InputT          input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OutputT         output_items[ITEMS_PER_THREAD],     ///< [out] Items to exchange, converting between <em>blocked</em> and <em>striped</em> arrangements.
        OffsetT         ranks[ITEMS_PER_THREAD],    ///< [in] Corresponding scatter ranks
        Int2Type<true> /*time_slicing*/)
    {
        InputT temp_items[ITEMS_PER_THREAD];

        #pragma unroll
        for (int SLICE = 0; SLICE < TIME_SLICES; SLICE++)
        {
            const int SLICE_OFFSET  = SLICE * TIME_SLICED_ITEMS;
            const int SLICE_OOB     = SLICE_OFFSET + TIME_SLICED_ITEMS;

            CTA_SYNC();

            #pragma unroll
            for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
            {
                int item_offset = ranks[ITEM] - SLICE_OFFSET;
                if ((item_offset >= 0) && (item_offset < WARP_TIME_SLICED_ITEMS))
                {
                    if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
                    temp_storage.buff[item_offset] = input_items[ITEM];
                }
            }

            CTA_SYNC();

            #pragma unroll
            for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
            {
                // Read a strip of items
                const int STRIP_OFFSET  = ITEM * BLOCK_THREADS;
                const int STRIP_OOB     = STRIP_OFFSET + BLOCK_THREADS;

                if ((SLICE_OFFSET < STRIP_OOB) && (SLICE_OOB > STRIP_OFFSET))
                {
                    int item_offset = STRIP_OFFSET + linear_tid - SLICE_OFFSET;
                    if ((item_offset >= 0) && (item_offset < TIME_SLICED_ITEMS))
                    {
                        if (INSERT_PADDING) item_offset += item_offset >> LOG_SMEM_BANKS;
                        temp_items[ITEM] = temp_storage.buff[item_offset];
                    }
                }
            }
        }

        // Copy
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            output_items[ITEM] = temp_items[ITEM];
        }
    }


public:

    /******************************************************************//**
     * \name Collective constructors
     *********************************************************************/
    //@{

    /**
     * \brief Collective constructor using a private static allocation of shared memory as temporary storage.
     */
    __device__ __forceinline__ BlockExchange()
    :
        temp_storage(PrivateStorage()),
        linear_tid(RowMajorTid(BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z)),
        warp_id((WARPS == 1) ? 0 : linear_tid / WARP_THREADS),
        lane_id(LaneId()),
        warp_offset(warp_id * WARP_TIME_SLICED_ITEMS)
    {}


    /**
     * \brief Collective constructor using the specified memory allocation as temporary storage.
     */
    __device__ __forceinline__ BlockExchange(
        TempStorage &temp_storage)             ///< [in] Reference to memory allocation having layout type TempStorage
    :
        temp_storage(temp_storage.Alias()),
        linear_tid(RowMajorTid(BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z)),
        lane_id(LaneId()),
        warp_id((WARPS == 1) ? 0 : linear_tid / WARP_THREADS),
        warp_offset(warp_id * WARP_TIME_SLICED_ITEMS)
    {}


    //@}  end member group
    /******************************************************************//**
     * \name Structured exchanges
     *********************************************************************/
    //@{

    /**
     * \brief Transposes data items from <em>striped</em> arrangement to <em>blocked</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \par Snippet
     * The code snippet below illustrates the conversion from a "striped" to a "blocked" arrangement
     * of 512 integer items partitioned across 128 threads where each thread owns 4 items.
     * \par
     * \code
     * #include <cub/cub.cuh>   // or equivalently <cub/block/block_exchange.cuh>
     *
     * __global__ void ExampleKernel(int *d_data, ...)
     * {
     *     // Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each
     *     typedef cub::BlockExchange<int, 128, 4> BlockExchange;
     *
     *     // Allocate shared memory for BlockExchange
     *     __shared__ typename BlockExchange::TempStorage temp_storage;
     *
     *     // Load a tile of ordered data into a striped arrangement across block threads
     *     int thread_data[4];
     *     cub::LoadDirectStriped<128>(threadIdx.x, d_data, thread_data);
     *
     *     // Collectively exchange data into a blocked arrangement across threads
     *     BlockExchange(temp_storage).StripedToBlocked(thread_data, thread_data);
     *
     * \endcode
     * \par
     * Suppose the set of striped input \p thread_data across the block of threads is
     * <tt>{ [0,128,256,384], [1,129,257,385], ..., [127,255,383,511] }</tt> after loading from device-accessible memory.
     * The corresponding output \p thread_data in those threads will be
     * <tt>{ [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }</tt>.
     *
     */
    template <typename OutputT>
    __device__ __forceinline__ void StripedToBlocked(
        InputT      input_items[ITEMS_PER_THREAD],    ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD])   ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        StripedToBlocked(input_items, output_items, Int2Type<WARP_TIME_SLICING>());
    }


    /**
     * \brief Transposes data items from <em>blocked</em> arrangement to <em>striped</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \par Snippet
     * The code snippet below illustrates the conversion from a "blocked" to a "striped" arrangement
     * of 512 integer items partitioned across 128 threads where each thread owns 4 items.
     * \par
     * \code
     * #include <cub/cub.cuh>   // or equivalently <cub/block/block_exchange.cuh>
     *
     * __global__ void ExampleKernel(int *d_data, ...)
     * {
     *     // Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each
     *     typedef cub::BlockExchange<int, 128, 4> BlockExchange;
     *
     *     // Allocate shared memory for BlockExchange
     *     __shared__ typename BlockExchange::TempStorage temp_storage;
     *
     *     // Obtain a segment of consecutive items that are blocked across threads
     *     int thread_data[4];
     *     ...
     *
     *     // Collectively exchange data into a striped arrangement across threads
     *     BlockExchange(temp_storage).BlockedToStriped(thread_data, thread_data);
     *
     *     // Store data striped across block threads into an ordered tile
     *     cub::StoreDirectStriped<STORE_DEFAULT, 128>(threadIdx.x, d_data, thread_data);
     *
     * \endcode
     * \par
     * Suppose the set of blocked input \p thread_data across the block of threads is
     * <tt>{ [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }</tt>.
     * The corresponding output \p thread_data in those threads will be
     * <tt>{ [0,128,256,384], [1,129,257,385], ..., [127,255,383,511] }</tt> in
     * preparation for storing to device-accessible memory.
     *
     */
    template <typename OutputT>
    __device__ __forceinline__ void BlockedToStriped(
        InputT      input_items[ITEMS_PER_THREAD],    ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD])   ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        BlockedToStriped(input_items, output_items, Int2Type<WARP_TIME_SLICING>());
    }



    /**
     * \brief Transposes data items from <em>warp-striped</em> arrangement to <em>blocked</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \par Snippet
     * The code snippet below illustrates the conversion from a "warp-striped" to a "blocked" arrangement
     * of 512 integer items partitioned across 128 threads where each thread owns 4 items.
     * \par
     * \code
     * #include <cub/cub.cuh>   // or equivalently <cub/block/block_exchange.cuh>
     *
     * __global__ void ExampleKernel(int *d_data, ...)
     * {
     *     // Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each
     *     typedef cub::BlockExchange<int, 128, 4> BlockExchange;
     *
     *     // Allocate shared memory for BlockExchange
     *     __shared__ typename BlockExchange::TempStorage temp_storage;
     *
     *     // Load a tile of ordered data into a warp-striped arrangement across warp threads
     *     int thread_data[4];
     *     cub::LoadSWarptriped<LOAD_DEFAULT>(threadIdx.x, d_data, thread_data);
     *
     *     // Collectively exchange data into a blocked arrangement across threads
     *     BlockExchange(temp_storage).WarpStripedToBlocked(thread_data);
     *
     * \endcode
     * \par
     * Suppose the set of warp-striped input \p thread_data across the block of threads is
     * <tt>{ [0,32,64,96], [1,33,65,97], [2,34,66,98], ..., [415,447,479,511] }</tt>
     * after loading from device-accessible memory.  (The first 128 items are striped across
     * the first warp of 32 threads, the second 128 items are striped across the second warp, etc.)
     * The corresponding output \p thread_data in those threads will be
     * <tt>{ [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }</tt>.
     *
     */
    template <typename OutputT>
    __device__ __forceinline__ void WarpStripedToBlocked(
        InputT      input_items[ITEMS_PER_THREAD],    ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD])   ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        WarpStripedToBlocked(input_items, output_items, Int2Type<WARP_TIME_SLICING>());
    }



    /**
     * \brief Transposes data items from <em>blocked</em> arrangement to <em>warp-striped</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \par Snippet
     * The code snippet below illustrates the conversion from a "blocked" to a "warp-striped" arrangement
     * of 512 integer items partitioned across 128 threads where each thread owns 4 items.
     * \par
     * \code
     * #include <cub/cub.cuh>   // or equivalently <cub/block/block_exchange.cuh>
     *
     * __global__ void ExampleKernel(int *d_data, ...)
     * {
     *     // Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each
     *     typedef cub::BlockExchange<int, 128, 4> BlockExchange;
     *
     *     // Allocate shared memory for BlockExchange
     *     __shared__ typename BlockExchange::TempStorage temp_storage;
     *
     *     // Obtain a segment of consecutive items that are blocked across threads
     *     int thread_data[4];
     *     ...
     *
     *     // Collectively exchange data into a warp-striped arrangement across threads
     *     BlockExchange(temp_storage).BlockedToWarpStriped(thread_data, thread_data);
     *
     *     // Store data striped across warp threads into an ordered tile
     *     cub::StoreDirectStriped<STORE_DEFAULT, 128>(threadIdx.x, d_data, thread_data);
     *
     * \endcode
     * \par
     * Suppose the set of blocked input \p thread_data across the block of threads is
     * <tt>{ [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }</tt>.
     * The corresponding output \p thread_data in those threads will be
     * <tt>{ [0,32,64,96], [1,33,65,97], [2,34,66,98], ..., [415,447,479,511] }</tt>
     * in preparation for storing to device-accessible memory. (The first 128 items are striped across
     * the first warp of 32 threads, the second 128 items are striped across the second warp, etc.)
     *
     */
    template <typename OutputT>
    __device__ __forceinline__ void BlockedToWarpStriped(
        InputT      input_items[ITEMS_PER_THREAD],    ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD])   ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        BlockedToWarpStriped(input_items, output_items, Int2Type<WARP_TIME_SLICING>());
    }



    //@}  end member group
    /******************************************************************//**
     * \name Scatter exchanges
     *********************************************************************/
    //@{


    /**
     * \brief Exchanges data items annotated by rank into <em>blocked</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \tparam OffsetT                              <b>[inferred]</b> Signed integer type for local offsets
     */
    template <typename OutputT, typename OffsetT>
    __device__ __forceinline__ void ScatterToBlocked(
        InputT      input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD],     ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD])            ///< [in] Corresponding scatter ranks
    {
        ScatterToBlocked(input_items, output_items, ranks, Int2Type<WARP_TIME_SLICING>());
    }



    /**
     * \brief Exchanges data items annotated by rank into <em>striped</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \tparam OffsetT                              <b>[inferred]</b> Signed integer type for local offsets
     */
    template <typename OutputT, typename OffsetT>
    __device__ __forceinline__ void ScatterToStriped(
        InputT      input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD],     ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD])            ///< [in] Corresponding scatter ranks
    {
        ScatterToStriped(input_items, output_items, ranks, Int2Type<WARP_TIME_SLICING>());
    }



    /**
     * \brief Exchanges data items annotated by rank into <em>striped</em> arrangement.  Items with rank -1 are not exchanged.
     *
     * \par
     * - \smemreuse
     *
     * \tparam OffsetT                              <b>[inferred]</b> Signed integer type for local offsets
     */
    template <typename OutputT, typename OffsetT>
    __device__ __forceinline__ void ScatterToStripedGuarded(
        InputT      input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD],     ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD])            ///< [in] Corresponding scatter ranks
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = ranks[ITEM];
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            if (ranks[ITEM] >= 0)
                temp_storage.buff[item_offset] = input_items[ITEM];
        }

        CTA_SYNC();

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = int(ITEM * BLOCK_THREADS) + linear_tid;
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            output_items[ITEM] = temp_storage.buff[item_offset];
        }
    }




    /**
     * \brief Exchanges valid data items annotated by rank into <em>striped</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \tparam OffsetT                              <b>[inferred]</b> Signed integer type for local offsets
     * \tparam ValidFlag                            <b>[inferred]</b> FlagT type denoting which items are valid
     */
    template <typename OutputT, typename OffsetT, typename ValidFlag>
    __device__ __forceinline__ void ScatterToStripedFlagged(
        InputT      input_items[ITEMS_PER_THREAD],      ///< [in] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OutputT     output_items[ITEMS_PER_THREAD],     ///< [out] Items from exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD],            ///< [in] Corresponding scatter ranks
        ValidFlag   is_valid[ITEMS_PER_THREAD])         ///< [in] Corresponding flag denoting item validity
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = ranks[ITEM];
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            if (is_valid[ITEM])
                temp_storage.buff[item_offset] = input_items[ITEM];
        }

        CTA_SYNC();

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = int(ITEM * BLOCK_THREADS) + linear_tid;
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            output_items[ITEM] = temp_storage.buff[item_offset];
        }
    }


    //@}  end member group



#ifndef DOXYGEN_SHOULD_SKIP_THIS    // Do not document


    __device__ __forceinline__ void StripedToBlocked(
        InputT      items[ITEMS_PER_THREAD])   ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        StripedToBlocked(items, items);
    }

    __device__ __forceinline__ void BlockedToStriped(
        InputT      items[ITEMS_PER_THREAD])   ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        BlockedToStriped(items, items);
    }

    __device__ __forceinline__ void WarpStripedToBlocked(
        InputT      items[ITEMS_PER_THREAD])    ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        WarpStripedToBlocked(items, items);
    }

    __device__ __forceinline__ void BlockedToWarpStriped(
        InputT      items[ITEMS_PER_THREAD])    ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
    {
        BlockedToWarpStriped(items, items);
    }

    template <typename OffsetT>
    __device__ __forceinline__ void ScatterToBlocked(
        InputT      items[ITEMS_PER_THREAD],    ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD])    ///< [in] Corresponding scatter ranks
    {
        ScatterToBlocked(items, items, ranks);
    }

    template <typename OffsetT>
    __device__ __forceinline__ void ScatterToStriped(
        InputT      items[ITEMS_PER_THREAD],    ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD])    ///< [in] Corresponding scatter ranks
    {
        ScatterToStriped(items, items, ranks);
    }

    template <typename OffsetT>
    __device__ __forceinline__ void ScatterToStripedGuarded(
        InputT      items[ITEMS_PER_THREAD],    ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD])    ///< [in] Corresponding scatter ranks
    {
        ScatterToStripedGuarded(items, items, ranks);
    }

    template <typename OffsetT, typename ValidFlag>
    __device__ __forceinline__ void ScatterToStripedFlagged(
        InputT      items[ITEMS_PER_THREAD],        ///< [in-out] Items to exchange, converting between <em>striped</em> and <em>blocked</em> arrangements.
        OffsetT     ranks[ITEMS_PER_THREAD],        ///< [in] Corresponding scatter ranks
        ValidFlag   is_valid[ITEMS_PER_THREAD])     ///< [in] Corresponding flag denoting item validity
    {
        ScatterToStriped(items, items, ranks, is_valid);
    }

#endif // DOXYGEN_SHOULD_SKIP_THIS


};


#ifndef DOXYGEN_SHOULD_SKIP_THIS    // Do not document


template <
    typename    T,
    int         ITEMS_PER_THREAD,
    int         LOGICAL_WARP_THREADS    = CUB_PTX_WARP_THREADS,
    int         PTX_ARCH                = CUB_PTX_ARCH>
class WarpExchange
{
private:

    /******************************************************************************
     * Constants
     ******************************************************************************/

    /// Constants
    enum
    {
        // Whether the logical warp size and the PTX warp size coincide
        IS_ARCH_WARP = (LOGICAL_WARP_THREADS == CUB_WARP_THREADS(PTX_ARCH)),

        WARP_ITEMS                  = (ITEMS_PER_THREAD * LOGICAL_WARP_THREADS) + 1,

        LOG_SMEM_BANKS              = CUB_LOG_SMEM_BANKS(PTX_ARCH),
        SMEM_BANKS                  = 1 << LOG_SMEM_BANKS,

        // Insert padding if the number of items per thread is a power of two and > 4 (otherwise we can typically use 128b loads)
        INSERT_PADDING              = (ITEMS_PER_THREAD > 4) && (PowerOfTwo<ITEMS_PER_THREAD>::VALUE),
        PADDING_ITEMS               = (INSERT_PADDING) ? (WARP_ITEMS >> LOG_SMEM_BANKS) : 0,
    };

    /******************************************************************************
     * Type definitions
     ******************************************************************************/

    /// Shared memory storage layout type
    struct _TempStorage
    {
        T buff[WARP_ITEMS + PADDING_ITEMS];
    };

public:

    /// \smemstorage{WarpExchange}
    struct TempStorage : Uninitialized<_TempStorage> {};

private:


    /******************************************************************************
     * Thread fields
     ******************************************************************************/

    _TempStorage    &temp_storage;
    int             lane_id;

public:

    /******************************************************************************
     * Construction
     ******************************************************************************/

    /// Constructor
    __device__ __forceinline__ WarpExchange(
        TempStorage &temp_storage)
    :
        temp_storage(temp_storage.Alias()),
        lane_id(IS_ARCH_WARP ?
            LaneId() :
            LaneId() % LOGICAL_WARP_THREADS)
    {}


    /******************************************************************************
     * Interface
     ******************************************************************************/

    /**
     * \brief Exchanges valid data items annotated by rank into <em>striped</em> arrangement.
     *
     * \par
     * - \smemreuse
     *
     * \tparam OffsetT                              <b>[inferred]</b> Signed integer type for local offsets
     */
    template <typename OffsetT>
    __device__ __forceinline__ void ScatterToStriped(
        T               items[ITEMS_PER_THREAD],        ///< [in-out] Items to exchange
        OffsetT         ranks[ITEMS_PER_THREAD])        ///< [in] Corresponding scatter ranks
    {
        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            if (INSERT_PADDING) ranks[ITEM] = SHR_ADD(ranks[ITEM], LOG_SMEM_BANKS, ranks[ITEM]);
            temp_storage.buff[ranks[ITEM]] = items[ITEM];
        }

        WARP_SYNC(0xffffffff);

        #pragma unroll
        for (int ITEM = 0; ITEM < ITEMS_PER_THREAD; ITEM++)
        {
            int item_offset = (ITEM * LOGICAL_WARP_THREADS) + lane_id;
            if (INSERT_PADDING) item_offset = SHR_ADD(item_offset, LOG_SMEM_BANKS, item_offset);
            items[ITEM] = temp_storage.buff[item_offset];
        }
    }

};




#endif // DOXYGEN_SHOULD_SKIP_THIS





}               // CUB namespace
CUB_NS_POSTFIX  // Optional outer namespace(s)