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xgboost/cub/cub/block/specializations/block_scan_warp_scans.cuh  view on Meta::CPAN

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

/**
 * \file
 * cub::BlockScanWarpscans provides warpscan-based variants of parallel prefix scan across a CUDA threadblock.
 */

#pragma once

#include "../../util_arch.cuh"
#include "../../util_ptx.cuh"
#include "../../warp/warp_scan.cuh"
#include "../../util_namespace.cuh"

/// Optional outer namespace(s)
CUB_NS_PREFIX

/// CUB namespace
namespace cub {

/**
 * \brief BlockScanWarpScans provides warpscan-based variants of parallel prefix scan across a CUDA threadblock.
 */
template <
    typename    T,
    int         BLOCK_DIM_X,    ///< The thread block length in threads along the X dimension
    int         BLOCK_DIM_Y,    ///< The thread block length in threads along the Y dimension
    int         BLOCK_DIM_Z,    ///< The thread block length in threads along the Z dimension
    int         PTX_ARCH>       ///< The PTX compute capability for which to to specialize this collective
struct BlockScanWarpScans
{
    //---------------------------------------------------------------------
    // Types and constants
    //---------------------------------------------------------------------

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

        /// 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, PTX_ARCH> WarpScanT;

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

    /// Shared memory storage layout type

    struct __align__(32) _TempStorage
    {
        T                               warp_aggregates[WARPS];
        typename WarpScanT::TempStorage warp_scan[WARPS];           ///< Buffer for warp-synchronous scans
        T                               block_prefix;               ///< Shared prefix for the entire threadblock
    };


    /// 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
    //---------------------------------------------------------------------

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

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