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xgboost/cub/cub/warp/specializations/warp_reduce_smem.cuh  view on Meta::CPAN

 * Copyright (c) 2011-2016, NVIDIA CORPORATION.  All rights reserved.
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 * modification, are permitted provided that the following conditions are met:
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 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the NVIDIA CORPORATION nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NVIDIA CORPORATION BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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/**
 * \file
 * cub::WarpReduceSmem provides smem-based variants of parallel reduction of items partitioned across a CUDA thread warp.
 */

#pragma once

#include "../../thread/thread_operators.cuh"
#include "../../thread/thread_load.cuh"
#include "../../thread/thread_store.cuh"
#include "../../util_type.cuh"
#include "../../util_namespace.cuh"

/// Optional outer namespace(s)
CUB_NS_PREFIX

/// CUB namespace
namespace cub {

/**
 * \brief WarpReduceSmem provides smem-based variants of parallel reduction of items partitioned across a CUDA thread warp.
 */
template <
    typename    T,                      ///< Data type being reduced
    int         LOGICAL_WARP_THREADS,   ///< Number of threads per logical warp
    int         PTX_ARCH>               ///< The PTX compute capability for which to to specialize this collective
struct WarpReduceSmem
{
    /******************************************************************************
     * Constants and type definitions
     ******************************************************************************/

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

        /// Whether the logical warp size is a power-of-two
        IS_POW_OF_TWO = PowerOfTwo<LOGICAL_WARP_THREADS>::VALUE,

        /// The number of warp scan steps
        STEPS = Log2<LOGICAL_WARP_THREADS>::VALUE,

        /// The number of threads in half a warp
        HALF_WARP_THREADS = 1 << (STEPS - 1),

        /// The number of shared memory elements per warp
        WARP_SMEM_ELEMENTS =  LOGICAL_WARP_THREADS + HALF_WARP_THREADS,

        /// FlagT status (when not using ballot)
        UNSET   = 0x0,  // Is initially unset
        SET     = 0x1,  // Is initially set
        SEEN    = 0x2,  // Has seen another head flag from a successor peer
    };

    /// Shared memory flag type
    typedef unsigned char SmemFlag;

    /// Shared memory storage layout type (1.5 warps-worth of elements for each warp)
    struct _TempStorage
    {
        T           reduce[WARP_SMEM_ELEMENTS];
        SmemFlag    flags[WARP_SMEM_ELEMENTS];
    };

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


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

    _TempStorage    &temp_storage;
    unsigned int    lane_id;
    unsigned int    member_mask;


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

    /// Constructor
    __device__ __forceinline__ WarpReduceSmem(
        TempStorage     &temp_storage)
    :
        temp_storage(temp_storage.Alias()),
        lane_id(IS_ARCH_WARP ?
            LaneId() :
            LaneId() % LOGICAL_WARP_THREADS),
        member_mask(!IS_POW_OF_TWO ?
            (0xffffffff >> (32 - LOGICAL_WARP_THREADS)) :                                       // non-power-of-two subwarps cannot be tiled
            (0xffffffff >> (32 - LOGICAL_WARP_THREADS)) << (LaneId() / LOGICAL_WARP_THREADS))
    {}