/******************************************************************************
 * Copyright (c) 2011, Duane Merrill.  All rights reserved.
 * Copyright (c) 2011-2018, NVIDIA CORPORATION.  All rights reserved.
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 *       names of its contributors may be used to endorse or promote products
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/**
 * @file
 * cub::BlockScanWarpscans provides warpscan-based variants of 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/detail/uninitialized_copy.cuh>
#include <cub/util_ptx.cuh>
#include <cub/warp/warp_scan.cuh>

CUB_NAMESPACE_BEGIN

/**
 * @brief BlockScanWarpScans provides warpscan-based variants of parallel prefix scan across a CUDA
 *        thread block.
 *
 * @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 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, int LEGACY_PTX_ARCH = 0>
struct BlockScanWarpScans
{
    //---------------------------------------------------------------------
    // Types and constants
    //---------------------------------------------------------------------

    /// Constants
    enum
    {
        /// Number of warp threads
        WARP_THREADS = CUB_WARP_THREADS(0),

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

        /// Number of active warps
        WARPS = (BLOCK_THREADS + WARP_THREADS - 1) / WARP_THREADS,
    };

    ///  WarpScan utility type
    typedef WarpScan<T, WARP_THREADS> WarpScanT;

    ///  WarpScan utility type
    typedef WarpScan<T, WARPS> WarpAggregateScan;

    /// Shared memory storage layout type

    struct __align__(32) _TempStorage
    {
      T warp_aggregates[WARPS];

      /// Buffer for warp-synchronous scans
      typename WarpScanT::TempStorage warp_scan[WARPS];

      /// Shared prefix for the entire thread block
      T block_prefix;
    };


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


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

    // Thread fields
    _TempStorage    &temp_storage;
    unsigned int    linear_tid;
    unsigned int    warp_id;
    unsigned int    lane_id;


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

    /// Constructor
    __device__ __forceinline__ BlockScanWarpScans(
        TempStorage &temp_storage)
    :
        temp_storage(temp_storage.Alias()),
        linear_tid(RowMajorTid(BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z)),
        warp_id((WARPS == 1) ? 0 : linear_tid / WARP_THREADS),
        lane_id(LaneId())
    {}


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

    /**
     * @param[out] warp_prefix
     *   The calling thread's partial reduction
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[out] block_aggregate
     *   Threadblock-wide aggregate reduction of input items
     */
    template <typename ScanOp, int WARP>
    __device__ __forceinline__ void ApplyWarpAggregates(T &warp_prefix,
                                                        ScanOp scan_op,
                                                        T &block_aggregate,
                                                        Int2Type<WARP> /*addend_warp*/)
    {
        if (warp_id == WARP)
            warp_prefix = block_aggregate;

        T addend = temp_storage.warp_aggregates[WARP];
        block_aggregate = scan_op(block_aggregate, addend);

        ApplyWarpAggregates(warp_prefix, scan_op, block_aggregate, Int2Type<WARP + 1>());
    }

    /**
     * @param[out] warp_prefix
     *   The calling thread's partial reduction
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[out] block_aggregat
     *   Threadblock-wide aggregate reduction of input items
     */
    template <typename ScanOp>
    __device__ __forceinline__ void ApplyWarpAggregates(T & /*warp_prefix*/,
                                                        ScanOp /*scan_op*/,
                                                        T & /*block_aggregate*/,
                                                        Int2Type<WARPS> /*addend_warp*/)
    {}

    /**
     * @brief Use the warp-wide aggregates to compute the calling warp's prefix.  Also returns
     *        block-wide aggregate in all threads.
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[in] warp_aggregate
     *   <b>[<em>lane</em><sub>WARP_THREADS - 1</sub> only]</b> Warp-wide aggregate reduction of
     *   input items
     *
     * @param[out] block_aggregate
     *   Threadblock-wide aggregate reduction of input items
     */
    template <typename ScanOp>
    __device__ __forceinline__ T ComputeWarpPrefix(ScanOp scan_op,
                                                   T warp_aggregate,
                                                   T &block_aggregate)
    {
        // Last lane in each warp shares its warp-aggregate
        if (lane_id == WARP_THREADS - 1)
        {
          detail::uninitialized_copy(temp_storage.warp_aggregates + warp_id,
                                     warp_aggregate);
        }

        CTA_SYNC();

        // Accumulate block aggregates and save the one that is our warp's prefix
        T warp_prefix;
        block_aggregate = temp_storage.warp_aggregates[0];

        // Use template unrolling (since the PTX backend can't handle unrolling it for SM1x)
        ApplyWarpAggregates(warp_prefix, scan_op, block_aggregate, Int2Type<1>());
/*
        #pragma unroll
        for (int WARP = 1; WARP < WARPS; ++WARP)
        {
            if (warp_id == WARP)
                warp_prefix = block_aggregate;

            T addend = temp_storage.warp_aggregates[WARP];
            block_aggregate = scan_op(block_aggregate, addend);
        }
*/

        return warp_prefix;
    }

    /**
     * @brief Use the warp-wide aggregates and initial-value to compute the calling warp's prefix.
     *        Also returns block-wide aggregate in all threads.
     *
     * @param[in] scan_op
     *   Binary scan operator
     *
     * @param[in] warp_aggregate
     *   <b>[<em>lane</em><sub>WARP_THREADS - 1</sub> only]</b> Warp-wide aggregate reduction of
     * input items
     *
     * @param[out] block_aggregate
     *   Threadblock-wide aggregate reduction of input items
     *
     * @param[in] initial_value
     *   Initial value to seed the exclusive scan
     */
    template <typename ScanOp>
    __device__ __forceinline__ T
    ComputeWarpPrefix(ScanOp scan_op, T warp_aggregate, T &block_aggregate, const T &initial_value)
    {
        T warp_prefix = ComputeWarpPrefix(scan_op, warp_aggregate, block_aggregate);

        warp_prefix = scan_op(initial_value, warp_prefix);

        if (warp_id == 0)
            warp_prefix = initial_value;

        return warp_prefix;
    }

    //---------------------------------------------------------------------
    // 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)
    {
        // Compute block-wide exclusive scan.  The exclusive output from tid0 is invalid.
        T block_aggregate;
        ExclusiveScan(input, exclusive_output, scan_op, 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.
     *
     * @param[in] input
     *   Calling thread's input items
     *
     * @param[out] exclusive_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 &exclusive_output, const T &initial_value, ScanOp scan_op)
    {
        T block_aggregate;
        ExclusiveScan(input, exclusive_output, initial_value, scan_op, 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. 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
     *
     * @param[out] block_aggregate
     *   Threadblock-wide aggregate reduction of input items
     */
    template <typename ScanOp>
    __device__ __forceinline__ void
    ExclusiveScan(T input, T &exclusive_output, ScanOp scan_op, T &block_aggregate)
    {
        // Compute warp scan in each warp.  The exclusive output from each lane0 is invalid.
        T inclusive_output;
        WarpScanT(temp_storage.warp_scan[warp_id]).Scan(input, inclusive_output, exclusive_output, scan_op);

        // Compute the warp-wide prefix and block-wide aggregate for each warp.  Warp prefix for warp0 is invalid.
        T warp_prefix = ComputeWarpPrefix(scan_op, inclusive_output, block_aggregate);

        // Apply warp prefix to our lane's partial
        if (warp_id != 0)
        {
            exclusive_output = scan_op(warp_prefix, exclusive_output);
            if (lane_id == 0)
                exclusive_output = warp_prefix;
        }
    }

    /**
     * @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] exclusive_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 &exclusive_output,
                                                  const T &initial_value,
                                                  ScanOp scan_op,
                                                  T &block_aggregate)
    {
        // Compute warp scan in each warp.  The exclusive output from each lane0 is invalid.
        T inclusive_output;
        WarpScanT(temp_storage.warp_scan[warp_id]).Scan(input, inclusive_output, exclusive_output, scan_op);

        // Compute the warp-wide prefix and block-wide aggregate for each warp
        T warp_prefix = ComputeWarpPrefix(scan_op, inclusive_output, block_aggregate, initial_value);

        // Apply warp prefix to our lane's partial
        exclusive_output = scan_op(warp_prefix, exclusive_output);
        if (lane_id == 0)
            exclusive_output = warp_prefix;
    }

    /**
     * @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] exclusive_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 &exclusive_output,
                                                  ScanOp scan_op,
                                                  BlockPrefixCallbackOp &block_prefix_callback_op)
    {
        // Compute block-wide exclusive scan.  The exclusive output from tid0 is invalid.
        T block_aggregate;
        ExclusiveScan(input, exclusive_output, scan_op, block_aggregate);

        // Use the first warp to determine the thread block prefix, returning the result in lane0
        if (warp_id == 0)
        {
            T block_prefix = block_prefix_callback_op(block_aggregate);
            if (lane_id == 0)
            {
              // Share the prefix with all threads
              detail::uninitialized_copy(&temp_storage.block_prefix,
                                         block_prefix);

              exclusive_output = block_prefix; // The block prefix is the exclusive output for tid0
            }
        }

        CTA_SYNC();

        // Incorporate thread block prefix into outputs
        T block_prefix = temp_storage.block_prefix;
        if (linear_tid > 0)
        {
            exclusive_output = scan_op(block_prefix, exclusive_output);
        }
    }


    //---------------------------------------------------------------------
    // 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] inclusive_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 &inclusive_output, ScanOp scan_op)
    {
        T block_aggregate;
        InclusiveScan(input, inclusive_output, scan_op, 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. Also provides every
     *        thread with the block-wide \p block_aggregate of all inputs.
     *
     * @param[in] input
     *   Calling thread's input item
     *
     * @param[out] inclusive_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 &inclusive_output, ScanOp scan_op, T &block_aggregate)
    {
        WarpScanT(temp_storage.warp_scan[warp_id]).InclusiveScan(input, inclusive_output, scan_op);

        // Compute the warp-wide prefix and block-wide aggregate for each warp.  Warp prefix for warp0 is invalid.
        T warp_prefix = ComputeWarpPrefix(scan_op, inclusive_output, block_aggregate);

        // Apply warp prefix to our lane's partial
        if (warp_id != 0)
        {
            inclusive_output = scan_op(warp_prefix, inclusive_output);
        }
    }

    /**
     * @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] exclusive_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 &exclusive_output,
                                                  ScanOp scan_op,
                                                  BlockPrefixCallbackOp &block_prefix_callback_op)
    {
        T block_aggregate;
        InclusiveScan(input, exclusive_output, scan_op, block_aggregate);

        // Use the first warp to determine the thread block prefix, returning the result in lane0
        if (warp_id == 0)
        {
            T block_prefix = block_prefix_callback_op(block_aggregate);
            if (lane_id == 0)
            {
                // Share the prefix with all threads
                detail::uninitialized_copy(&temp_storage.block_prefix,
                                           block_prefix);
            }
        }

        CTA_SYNC();

        // Incorporate thread block prefix into outputs
        T block_prefix = temp_storage.block_prefix;
        exclusive_output = scan_op(block_prefix, exclusive_output);
    }


};


CUB_NAMESPACE_END

