/******************************************************************************
 * Copyright (c) 2011, Duane Merrill.  All rights reserved.
 * Copyright (c) 2011-2018, NVIDIA CORPORATION.  All rights reserved.
 *
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 * 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.
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 *       names of its contributors may be used to endorse or promote products
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/**
 * @file
 * cub::BlockScanRaking provides variants of raking-based parallel prefix scan across a
 * CUDA thread block.
 */

#pragma once

#include <cub/config.cuh>

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

#include <cub/block/block_raking_layout.cuh>
#include <cub/detail/uninitialized_copy.cuh>
#include <cub/thread/thread_reduce.cuh>
#include <cub/thread/thread_scan.cuh>
#include <cub/util_ptx.cuh>
#include <cub/warp/warp_scan.cuh>

CUB_NAMESPACE_BEGIN

/**
 * @brief BlockScanRaking provides variants of raking-based parallel prefix scan across a CUDA
 * thread block.
 *
 * @tparam T
 *   Data type being scanned
 *
 * @tparam BLOCK_DIM_X
 *   The thread block length in threads along the X dimension
 *
 * @tparam BLOCK_DIM_Y
 *   The thread block length in threads along the Y dimension
 *
 * @tparam BLOCK_DIM_Z
 *   The thread block length in threads along the Z dimension
 *
 * @tparam MEMOIZE
 *   Whether or not to buffer outer raking scan partials to incur fewer shared memory reads at the
 * expense of higher register pressure
 *
 * @tparam LEGACY_PTX_ARCH
 *   The PTX compute capability for which to to specialize this collective
 */
template <typename T,
          int BLOCK_DIM_X,
          int BLOCK_DIM_Y,
          int BLOCK_DIM_Z,
          bool MEMOIZE,
          int LEGACY_PTX_ARCH = 0>
struct BlockScanRaking
{
    //---------------------------------------------------------------------
    // Types and constants
    //---------------------------------------------------------------------

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

    /// Layout type for padded thread block raking grid
    typedef BlockRakingLayout<T, BLOCK_THREADS> BlockRakingLayout;

    /// Constants
    enum
    {
        /// Number of raking threads
        RAKING_THREADS = BlockRakingLayout::RAKING_THREADS,

        /// Number of raking elements per warp synchronous raking thread
        SEGMENT_LENGTH = BlockRakingLayout::SEGMENT_LENGTH,

        /// Cooperative work can be entirely warp synchronous
        WARP_SYNCHRONOUS = (int(BLOCK_THREADS) == int(RAKING_THREADS)),
    };

    ///  WarpScan utility type
    typedef WarpScan<T, RAKING_THREADS> WarpScan;

    /// Shared memory storage layout type
    struct _TempStorage
    {
      /// Buffer for warp-synchronous scan
      typename WarpScan::TempStorage warp_scan;

      /// Padded thread block raking grid
      typename BlockRakingLayout::TempStorage raking_grid;

      /// Block aggregate
      T block_aggregate;
    };


    /// Alias wrapper allowing storage to be unioned
    struct TempStorage : Uninitialized<_TempStorage> {};


    //---------------------------------------------------------------------
    // Per-thread fields
    //---------------------------------------------------------------------

    // Thread fields
    _TempStorage    &temp_storage;
    unsigned int    linear_tid;
    T               cached_segment[SEGMENT_LENGTH];


    //---------------------------------------------------------------------
    // Utility methods
    //---------------------------------------------------------------------

    /**
     * @brief Templated reduction
     *
     * @param[in] raking_ptr
     *   Input array
     *
     * @param[in] scan_op
     *   Binary reduction operator
     *
     * @param[in] raking_partial
     *   Prefix to seed reduction with
     */
    template <int ITERATION, typename ScanOp>
    __device__ __forceinline__ T GuardedReduce(T *raking_ptr,
                                               ScanOp scan_op,
                                               T raking_partial,
                                               Int2Type<ITERATION> /*iteration*/)
    {
        if ((BlockRakingLayout::UNGUARDED) || (((linear_tid * SEGMENT_LENGTH) + ITERATION) < BLOCK_THREADS))
        {
            T addend = raking_ptr[ITERATION];
            raking_partial = scan_op(raking_partial, addend);
        }

        return GuardedReduce(raking_ptr, scan_op, raking_partial, Int2Type<ITERATION + 1>());
    }

    /**
     * @brief Templated reduction (base case)
     *
     * @param[in] raking_ptr
     *   Input array
     *
     * @param[in] scan_op
     *   Binary reduction operator
     *
     * @param[in] raking_partial
     *   Prefix to seed reduction with
     */
    template <typename ScanOp>
    __device__ __forceinline__ T GuardedReduce(T * /*raking_ptr*/,
                                               ScanOp /*scan_op*/,
                                               T raking_partial,
                                               Int2Type<SEGMENT_LENGTH> /*iteration*/)
    {
        return raking_partial;
    }

    /**
     * @brief Templated copy
     *
     * @param out
     *   [out] Out array
     *
     * @param in
     *   [in] Input array
     */
    template <int ITERATION>
    __device__ __forceinline__ void CopySegment(T *out, T *in, Int2Type<ITERATION> /*iteration*/)
    {
        out[ITERATION] = in[ITERATION];
        CopySegment(out, in, Int2Type<ITERATION + 1>());
    }

    /**
     * @brief Templated copy (base case)
     *
     * @param[out] out
     *   Out array
     *
     * @param[in] in
     *   Input array
     */
    __device__ __forceinline__ void CopySegment(T * /*out*/,
                                                T * /*in*/,
                                                Int2Type<SEGMENT_LENGTH> /*iteration*/)
    {}

    /// Performs upsweep raking reduction, returning the aggregate
    template <typename ScanOp>
    __device__ __forceinline__ T Upsweep(
        ScanOp scan_op)
    {
        T *smem_raking_ptr = BlockRakingLayout::RakingPtr(temp_storage.raking_grid, linear_tid);

        // Read data into registers
        CopySegment(cached_segment, smem_raking_ptr, Int2Type<0>());

        T raking_partial = cached_segment[0];

        return GuardedReduce(cached_segment, scan_op, raking_partial, Int2Type<1>());
    }


    /// Performs exclusive downsweep raking scan
    template <typename ScanOp>
    __device__ __forceinline__ void ExclusiveDownsweep(
        ScanOp          scan_op,
        T               raking_partial,
        bool            apply_prefix = true)
    {
        T *smem_raking_ptr = BlockRakingLayout::RakingPtr(temp_storage.raking_grid, linear_tid);

        // Read data back into registers
        if (!MEMOIZE)
        {
            CopySegment(cached_segment, smem_raking_ptr, Int2Type<0>());
        }

        internal::ThreadScanExclusive(cached_segment, cached_segment, scan_op, raking_partial, apply_prefix);

        // Write data back to smem
        CopySegment(smem_raking_ptr, cached_segment, Int2Type<0>());
    }


    /// Performs inclusive downsweep raking scan
    template <typename ScanOp>
    __device__ __forceinline__ void InclusiveDownsweep(
        ScanOp          scan_op,
        T               raking_partial,
        bool            apply_prefix = true)
    {
        T *smem_raking_ptr = BlockRakingLayout::RakingPtr(temp_storage.raking_grid, linear_tid);

        // Read data back into registers
        if (!MEMOIZE)
        {
            CopySegment(cached_segment, smem_raking_ptr, Int2Type<0>());
        }

        internal::ThreadScanInclusive(cached_segment, cached_segment, scan_op, raking_partial, apply_prefix);

        // Write data back to smem
        CopySegment(smem_raking_ptr, cached_segment, Int2Type<0>());
    }


    //---------------------------------------------------------------------
    // Constructors
    //---------------------------------------------------------------------

    /// Constructor
    __device__ __forceinline__ BlockScanRaking(
        TempStorage &temp_storage)
    :
        temp_storage(temp_storage.Alias()),
        linear_tid(RowMajorTid(BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z))
    {}


    //---------------------------------------------------------------------
    // Exclusive scans
    //---------------------------------------------------------------------

    /**
     * @brief Computes an exclusive thread block-wide prefix scan using the specified binary \p
     *        scan_op functor. Each thread contributes one input element. With no initial value,
     *        the output computed for <em>thread</em><sub>0</sub> is undefined.
     *
     * @param[in] input
     *   Calling thread's input item
     *
     * @param[out] exclusive_output
     *   Calling thread's output item (may be aliased to \p input)
     *
     * @param[in] scan_op
     *   Binary scan operator
     */
    template <typename ScanOp>
    __device__ __forceinline__ void ExclusiveScan(T input, T &exclusive_output, ScanOp scan_op)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            WarpScan(temp_storage.warp_scan).ExclusiveScan(input, exclusive_output, scan_op);
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                // Raking upsweep reduction across shared partials
                T upsweep_partial = Upsweep(scan_op);

                // Warp-synchronous scan
                T exclusive_partial;
                WarpScan(temp_storage.warp_scan).ExclusiveScan(upsweep_partial, exclusive_partial, scan_op);

                // Exclusive raking downsweep scan
                ExclusiveDownsweep(scan_op, exclusive_partial, (linear_tid != 0));
            }

            CTA_SYNC();

            // Grab thread prefix from shared memory
            exclusive_output = *placement_ptr;
        }
    }

    /**
     * @brief Computes an exclusive thread block-wide prefix scan using the specified binary \p
     * scan_op functor.  Each thread contributes one input element.
     *
     * @param[in] input
     *   Calling thread's input items
     *
     * @param[out] output
     *   Calling thread's output items (may be aliased to \p input)
     *
     * @param[in] initial_value
     *   Initial value to seed the exclusive scan
     *
     * @param[in] scan_op
     *   Binary scan operator
     */
    template <typename ScanOp>
    __device__ __forceinline__ void
    ExclusiveScan(T input, T &output, const T &initial_value, ScanOp scan_op)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            WarpScan(temp_storage.warp_scan).ExclusiveScan(input, output, initial_value, scan_op);
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                // Raking upsweep reduction across shared partials
                T upsweep_partial = Upsweep(scan_op);

                // Exclusive Warp-synchronous scan
                T exclusive_partial;
                WarpScan(temp_storage.warp_scan).ExclusiveScan(upsweep_partial, exclusive_partial, initial_value, scan_op);

                // Exclusive raking downsweep scan
                ExclusiveDownsweep(scan_op, exclusive_partial);
            }

            CTA_SYNC();

            // Grab exclusive partial from shared memory
            output = *placement_ptr;
        }
    }

    /**
     * @brief Computes an exclusive thread block-wide prefix scan using the specified binary \p
     *        scan_op functor.  Each thread contributes one input element.  Also provides every
     *        thread with the block-wide \p block_aggregate of all inputs.  With no initial value,
     *        the output computed for <em>thread</em><sub>0</sub> is undefined.
     *
     * @param[in] input
     *   Calling thread's input item
     *
     * @param[out] output
     *   Calling thread's output item (may be aliased to \p input)
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[out] block_aggregate
     *   Threadblock-wide aggregate reduction of input items
     */
    template <typename ScanOp>
    __device__ __forceinline__ void
    ExclusiveScan(T input, T &output, ScanOp scan_op, T &block_aggregate)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            WarpScan(temp_storage.warp_scan).ExclusiveScan(input, output, scan_op, block_aggregate);
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                // Raking upsweep reduction across shared partials
                T upsweep_partial= Upsweep(scan_op);

                // Warp-synchronous scan
                T inclusive_partial;
                T exclusive_partial;
                WarpScan(temp_storage.warp_scan).Scan(upsweep_partial, inclusive_partial, exclusive_partial, scan_op);

                // Exclusive raking downsweep scan
                ExclusiveDownsweep(scan_op, exclusive_partial, (linear_tid != 0));

                // Broadcast aggregate to all threads
                if (linear_tid == RAKING_THREADS - 1)
                    temp_storage.block_aggregate = inclusive_partial;
            }

            CTA_SYNC();

            // Grab thread prefix from shared memory
            output = *placement_ptr;

            // Retrieve block aggregate
            block_aggregate = temp_storage.block_aggregate;
        }
    }

    /**
     * @brief Computes an exclusive thread block-wide prefix scan using the specified binary \p
     *        scan_op functor.  Each thread contributes one input element.  Also provides every
     *        thread with the block-wide \p block_aggregate of all inputs.
     *
     * @param[in] input
     *   Calling thread's input items
     *
     * @param[out] output
     *   Calling thread's output items (may be aliased to \p input)
     *
     * @param[in] initial_value
     *   Initial value to seed the exclusive scan
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[out] block_aggregate
     *   Threadblock-wide aggregate reduction of input items
     */
    template <typename ScanOp>
    __device__ __forceinline__ void
    ExclusiveScan(T input, T &output, const T &initial_value, ScanOp scan_op, T &block_aggregate)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            WarpScan(temp_storage.warp_scan).ExclusiveScan(input, output, initial_value, scan_op, block_aggregate);
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                // Raking upsweep reduction across shared partials
                T upsweep_partial = Upsweep(scan_op);

                // Warp-synchronous scan
                T exclusive_partial;
                WarpScan(temp_storage.warp_scan).ExclusiveScan(upsweep_partial, exclusive_partial, initial_value, scan_op, block_aggregate);

                // Exclusive raking downsweep scan
                ExclusiveDownsweep(scan_op, exclusive_partial);

                // Broadcast aggregate to other threads
                if (linear_tid == 0)
                    temp_storage.block_aggregate = block_aggregate;
            }

            CTA_SYNC();

            // Grab exclusive partial from shared memory
            output = *placement_ptr;

            // Retrieve block aggregate
            block_aggregate = temp_storage.block_aggregate;
        }
    }

    /**
     * @brief Computes an exclusive thread block-wide prefix scan using the specified binary \p
     *        scan_op functor.  Each thread contributes one input element.  the call-back functor \p
     *        block_prefix_callback_op is invoked by the first warp in the block, and the value
     *        returned by <em>lane</em><sub>0</sub> in that warp is used as the "seed" value that
     *        logically prefixes the thread block's scan inputs.  Also provides every thread with
     *        the block-wide \p block_aggregate of all inputs.
     *
     * @param[in] input
     *   Calling thread's input item
     *
     * @param[out] output
     *   Calling thread's output item (may be aliased to \p input)
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[in-out] block_prefix_callback_op
     *   <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a thread
     *   block-wide prefix to be applied to all inputs.
     */
    template <typename ScanOp, typename BlockPrefixCallbackOp>
    __device__ __forceinline__ void ExclusiveScan(T input,
                                                  T &output,
                                                  ScanOp scan_op,
                                                  BlockPrefixCallbackOp &block_prefix_callback_op)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            T block_aggregate;
            WarpScan warp_scan(temp_storage.warp_scan);
            warp_scan.ExclusiveScan(input, output, scan_op, block_aggregate);

            // Obtain warp-wide prefix in lane0, then broadcast to other lanes
            T block_prefix = block_prefix_callback_op(block_aggregate);
            block_prefix = warp_scan.Broadcast(block_prefix, 0);

            output = scan_op(block_prefix, output);
            if (linear_tid == 0)
                output = block_prefix;
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                WarpScan warp_scan(temp_storage.warp_scan);

                // Raking upsweep reduction across shared partials
                T upsweep_partial = Upsweep(scan_op);

                // Warp-synchronous scan
                T exclusive_partial, block_aggregate;
                warp_scan.ExclusiveScan(upsweep_partial, exclusive_partial, scan_op, block_aggregate);

                // Obtain block-wide prefix in lane0, then broadcast to other lanes
                T block_prefix = block_prefix_callback_op(block_aggregate);
                block_prefix = warp_scan.Broadcast(block_prefix, 0);

                // Update prefix with warpscan exclusive partial
                T downsweep_prefix = scan_op(block_prefix, exclusive_partial);
                if (linear_tid == 0)
                    downsweep_prefix = block_prefix;

                // Exclusive raking downsweep scan
                ExclusiveDownsweep(scan_op, downsweep_prefix);
            }

            CTA_SYNC();

            // Grab thread prefix from shared memory
            output = *placement_ptr;
        }
    }


    //---------------------------------------------------------------------
    // Inclusive scans
    //---------------------------------------------------------------------

    /**
     * @brief Computes an inclusive thread block-wide prefix scan using the specified binary \p
     *        scan_op functor. Each thread contributes one input element.
     *
     * @param[in] input
     *   Calling thread's input item
     *
     * @param[out] output
     *   Calling thread's output item (may be aliased to \p input)
     *
     * @param[in] scan_op
     *   Binary scan operator
     */
    template <typename ScanOp>
    __device__ __forceinline__ void InclusiveScan(T input, T &output, ScanOp scan_op)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            WarpScan(temp_storage.warp_scan).InclusiveScan(input, output, scan_op);
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                // Raking upsweep reduction across shared partials
                T upsweep_partial = Upsweep(scan_op);

                // Exclusive Warp-synchronous scan
                T exclusive_partial;
                WarpScan(temp_storage.warp_scan).ExclusiveScan(upsweep_partial, exclusive_partial, scan_op);

                // Inclusive raking downsweep scan
                InclusiveDownsweep(scan_op, exclusive_partial, (linear_tid != 0));
            }

            CTA_SYNC();

            // Grab thread prefix from shared memory
            output = *placement_ptr;
        }
    }

    /**
     * @brief Computes an inclusive thread block-wide prefix scan using the specified binary \p
     *        scan_op functor. Each thread contributes one input element.  Also provides every
     *        thread with the block-wide \p block_aggregate of all inputs.
     *
     * @param[in] input
     *   Calling thread's input item
     *
     * @param[out] output
     *   Calling thread's output item (may be aliased to \p input)
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[out] block_aggregate
     *   Threadblock-wide aggregate reduction of input items
     */
    template <typename ScanOp>
    __device__ __forceinline__ void
    InclusiveScan(T input, T &output, ScanOp scan_op, T &block_aggregate)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            WarpScan(temp_storage.warp_scan).InclusiveScan(input, output, scan_op, block_aggregate);
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                // Raking upsweep reduction across shared partials
                T upsweep_partial = Upsweep(scan_op);

                // Warp-synchronous scan
                T inclusive_partial;
                T exclusive_partial;
                WarpScan(temp_storage.warp_scan).Scan(upsweep_partial, inclusive_partial, exclusive_partial, scan_op);

                // Inclusive raking downsweep scan
                InclusiveDownsweep(scan_op, exclusive_partial, (linear_tid != 0));

                // Broadcast aggregate to all threads
                if (linear_tid == RAKING_THREADS - 1)
                    temp_storage.block_aggregate = inclusive_partial;
            }

            CTA_SYNC();

            // Grab thread prefix from shared memory
            output = *placement_ptr;

            // Retrieve block aggregate
            block_aggregate = temp_storage.block_aggregate;
        }
    }

    /**
     * @brief Computes an inclusive thread block-wide prefix scan using the specified binary \p
     *        scan_op functor.  Each thread contributes one input element.  the call-back functor \p
     *        block_prefix_callback_op is invoked by the first warp in the block, and the value
     *        returned by <em>lane</em><sub>0</sub> in that warp is used as the "seed" value that
     *        logically prefixes the thread block's scan inputs.  Also provides every thread with
     *        the block-wide \p block_aggregate of all inputs.
     *
     * @param[in] input
     *   Calling thread's input item
     *
     * @param[out] output
     *   Calling thread's output item (may be aliased to \p input)
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[in-out] block_prefix_callback_op
     *   <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a thread
     *   block-wide prefix to be applied to all inputs.
     */
    template <typename ScanOp, typename BlockPrefixCallbackOp>
    __device__ __forceinline__ void InclusiveScan(T input,
                                                  T &output,
                                                  ScanOp scan_op,
                                                  BlockPrefixCallbackOp &block_prefix_callback_op)
    {
        if (WARP_SYNCHRONOUS)
        {
            // Short-circuit directly to warp-synchronous scan
            T block_aggregate;
            WarpScan warp_scan(temp_storage.warp_scan);
            warp_scan.InclusiveScan(input, output, scan_op, block_aggregate);

            // Obtain warp-wide prefix in lane0, then broadcast to other lanes
            T block_prefix = block_prefix_callback_op(block_aggregate);
            block_prefix = warp_scan.Broadcast(block_prefix, 0);

            // Update prefix with exclusive warpscan partial
            output = scan_op(block_prefix, output);
        }
        else
        {
            // Place thread partial into shared memory raking grid
            T *placement_ptr = BlockRakingLayout::PlacementPtr(temp_storage.raking_grid, linear_tid);
            detail::uninitialized_copy(placement_ptr, input);

            CTA_SYNC();

            // Reduce parallelism down to just raking threads
            if (linear_tid < RAKING_THREADS)
            {
                WarpScan warp_scan(temp_storage.warp_scan);

                // Raking upsweep reduction across shared partials
                T upsweep_partial = Upsweep(scan_op);

                // Warp-synchronous scan
                T exclusive_partial, block_aggregate;
                warp_scan.ExclusiveScan(upsweep_partial, exclusive_partial, scan_op, block_aggregate);

                // Obtain block-wide prefix in lane0, then broadcast to other lanes
                T block_prefix = block_prefix_callback_op(block_aggregate);
                block_prefix = warp_scan.Broadcast(block_prefix, 0);

                // Update prefix with warpscan exclusive partial
                T downsweep_prefix = scan_op(block_prefix, exclusive_partial);
                if (linear_tid == 0)
                    downsweep_prefix = block_prefix;

                // Inclusive raking downsweep scan
                InclusiveDownsweep(scan_op, downsweep_prefix);
            }

            CTA_SYNC();

            // Grab thread prefix from shared memory
            output = *placement_ptr;
        }
    }

};


CUB_NAMESPACE_END

