block_scan_warp_scans3.cuh

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 * Copyright (c) 2011, Duane Merrill.  All rights reserved.
 * Copyright (c) 2011-2018, NVIDIA CORPORATION.  All rights reserved.
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#pragma once

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

CUB_NS_PREFIX

namespace cub {

template <
    typename    T,
    int         BLOCK_DIM_X,    
    int         BLOCK_DIM_Y,    
    int         BLOCK_DIM_Z,    
    int         PTX_ARCH>       
struct BlockScanWarpScans
{
    //---------------------------------------------------------------------
    // Types and constants
    //---------------------------------------------------------------------

    enum
    {
        BLOCK_THREADS = BLOCK_DIM_X * BLOCK_DIM_Y * BLOCK_DIM_Z,

        INNER_WARP_THREADS = CUB_WARP_THREADS(PTX_ARCH),
        OUTER_WARP_THREADS = BLOCK_THREADS / INNER_WARP_THREADS,

        OUTER_WARPS = INNER_WARP_THREADS
    };

    typedef WarpScan<T, OUTER_WARP_THREADS, PTX_ARCH> OuterWarpScanT;

    typedef WarpScan<T, INNER_WARP_THREADS, PTX_ARCH> InnerWarpScanT;

    typedef typename OuterWarpScanT::TempStorage OuterScanArray[OUTER_WARPS];


    struct _TempStorage
    {
        union Aliasable
        {
            Uninitialized<OuterScanArray>           outer_warp_scan;  
            typename InnerWarpScanT::TempStorage    inner_warp_scan;  

        } aliasable;

        T                               warp_aggregates[OUTER_WARPS];

        T                               block_aggregate;                           
    };


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

    __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((OUTER_WARPS == 1) ? 0 : linear_tid / OUTER_WARP_THREADS),
        lane_id((OUTER_WARPS == 1) ? linear_tid : linear_tid % OUTER_WARP_THREADS)
    {}


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

    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);
    }


    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);
    }


    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;
        OuterWarpScanT(temp_storage.aliasable.outer_warp_scan.Alias()[warp_id]).Scan(
            input, inclusive_output, exclusive_output, scan_op);

        // Share outer warp total
        if (lane_id == OUTER_WARP_THREADS - 1)
            temp_storage.warp_aggregates[warp_id] = inclusive_output;

        CTA_SYNC();

        if (linear_tid < INNER_WARP_THREADS)
        {
            T outer_warp_input = temp_storage.warp_aggregates[linear_tid];
            T outer_warp_exclusive;

            InnerWarpScanT(temp_storage.aliasable.inner_warp_scan).ExclusiveScan(
                outer_warp_input, outer_warp_exclusive, scan_op, block_aggregate);

            temp_storage.block_aggregate                = block_aggregate;
            temp_storage.warp_aggregates[linear_tid]    = outer_warp_exclusive;
        }

        CTA_SYNC();

        if (warp_id != 0)
        {
            // Retrieve block aggregate
            block_aggregate = temp_storage.block_aggregate;

            // Apply warp prefix to our lane's partial
            T outer_warp_exclusive = temp_storage.warp_aggregates[warp_id];
            exclusive_output = scan_op(outer_warp_exclusive, exclusive_output);
            if (lane_id == 0)
                exclusive_output = outer_warp_exclusive;
        }
    }


    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;
        OuterWarpScanT(temp_storage.aliasable.outer_warp_scan.Alias()[warp_id]).Scan(
            input, inclusive_output, exclusive_output, scan_op);

        // Share outer warp total
        if (lane_id == OUTER_WARP_THREADS - 1)
        {
            temp_storage.warp_aggregates[warp_id] = inclusive_output;
        }

        CTA_SYNC();

        if (linear_tid < INNER_WARP_THREADS)
        {
            T outer_warp_input = temp_storage.warp_aggregates[linear_tid];
            T outer_warp_exclusive;

            InnerWarpScanT(temp_storage.aliasable.inner_warp_scan).ExclusiveScan(
                outer_warp_input, outer_warp_exclusive, initial_value, scan_op, block_aggregate);

            temp_storage.block_aggregate                = block_aggregate;
            temp_storage.warp_aggregates[linear_tid]    = outer_warp_exclusive;
        }

        CTA_SYNC();

        // Retrieve block aggregate
        block_aggregate = temp_storage.block_aggregate;

        // Apply warp prefix to our lane's partial
        T outer_warp_exclusive = temp_storage.warp_aggregates[warp_id];
        exclusive_output = scan_op(outer_warp_exclusive, exclusive_output);
        if (lane_id == 0)
            exclusive_output = outer_warp_exclusive;
    }


    template <
        typename ScanOp,
        typename BlockPrefixCallbackOp>
    __device__ __forceinline__ void ExclusiveScan(
        T                       input,                          
        T                       &exclusive_output,              
        ScanOp                  scan_op,                        
        BlockPrefixCallbackOp   &block_prefix_callback_op)      
    {
        // Compute warp scan in each warp.  The exclusive output from each lane0 is invalid.
        T inclusive_output;
        OuterWarpScanT(temp_storage.aliasable.outer_warp_scan.Alias()[warp_id]).Scan(
            input, inclusive_output, exclusive_output, scan_op);

        // Share outer warp total
        if (lane_id == OUTER_WARP_THREADS - 1)
            temp_storage.warp_aggregates[warp_id] = inclusive_output;

        CTA_SYNC();

        if (linear_tid < INNER_WARP_THREADS)
        {
            InnerWarpScanT inner_scan(temp_storage.aliasable.inner_warp_scan);

            T upsweep = temp_storage.warp_aggregates[linear_tid];
            T downsweep_prefix, block_aggregate;

            inner_scan.ExclusiveScan(upsweep, downsweep_prefix, scan_op, block_aggregate);

            // Use callback functor to get block prefix in lane0 and then broadcast to other lanes
            T block_prefix = block_prefix_callback_op(block_aggregate);
            block_prefix = inner_scan.Broadcast(block_prefix, 0);

            downsweep_prefix = scan_op(block_prefix, downsweep_prefix);
            if (linear_tid == 0)
                downsweep_prefix = block_prefix;

            temp_storage.warp_aggregates[linear_tid] = downsweep_prefix;
        }

        CTA_SYNC();

        // Apply warp prefix to our lane's partial (or assign it if partial is invalid)
        T outer_warp_exclusive = temp_storage.warp_aggregates[warp_id];
        exclusive_output = scan_op(outer_warp_exclusive, exclusive_output);
        if (lane_id == 0)
            exclusive_output = outer_warp_exclusive;
    }


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

    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);
    }


    template <typename ScanOp>
    __device__ __forceinline__ void InclusiveScan(
        T               input,                          
        T               &inclusive_output,              
        ScanOp          scan_op,                        
        T               &block_aggregate)               
    {
        // Compute warp scan in each warp.  The exclusive output from each lane0 is invalid.
        OuterWarpScanT(temp_storage.aliasable.outer_warp_scan.Alias()[warp_id]).InclusiveScan(
            input, inclusive_output, scan_op);

        // Share outer warp total
        if (lane_id == OUTER_WARP_THREADS - 1)
            temp_storage.warp_aggregates[warp_id] = inclusive_output;

        CTA_SYNC();

        if (linear_tid < INNER_WARP_THREADS)
        {
            T outer_warp_input = temp_storage.warp_aggregates[linear_tid];
            T outer_warp_exclusive;

            InnerWarpScanT(temp_storage.aliasable.inner_warp_scan).ExclusiveScan(
                outer_warp_input, outer_warp_exclusive, scan_op, block_aggregate);

            temp_storage.block_aggregate                = block_aggregate;
            temp_storage.warp_aggregates[linear_tid]    = outer_warp_exclusive;
        }

        CTA_SYNC();

        if (warp_id != 0)
        {
            // Retrieve block aggregate
            block_aggregate = temp_storage.block_aggregate;

            // Apply warp prefix to our lane's partial
            T outer_warp_exclusive = temp_storage.warp_aggregates[warp_id];
            inclusive_output = scan_op(outer_warp_exclusive, inclusive_output);
        }
    }


    template <
        typename ScanOp,
        typename BlockPrefixCallbackOp>
    __device__ __forceinline__ void InclusiveScan(
        T                       input,                          
        T                       &inclusive_output,              
        ScanOp                  scan_op,                        
        BlockPrefixCallbackOp   &block_prefix_callback_op)      
    {
        // Compute warp scan in each warp.  The exclusive output from each lane0 is invalid.
        OuterWarpScanT(temp_storage.aliasable.outer_warp_scan.Alias()[warp_id]).InclusiveScan(
            input, inclusive_output, scan_op);

        // Share outer warp total
        if (lane_id == OUTER_WARP_THREADS - 1)
            temp_storage.warp_aggregates[warp_id] = inclusive_output;

        CTA_SYNC();

        if (linear_tid < INNER_WARP_THREADS)
        {
            InnerWarpScanT inner_scan(temp_storage.aliasable.inner_warp_scan);

            T upsweep = temp_storage.warp_aggregates[linear_tid];
            T downsweep_prefix, block_aggregate;
            inner_scan.ExclusiveScan(upsweep, downsweep_prefix, scan_op, block_aggregate);

            // Use callback functor to get block prefix in lane0 and then broadcast to other lanes
            T block_prefix = block_prefix_callback_op(block_aggregate);
            block_prefix = inner_scan.Broadcast(block_prefix, 0);

            downsweep_prefix = scan_op(block_prefix, downsweep_prefix);
            if (linear_tid == 0)
                downsweep_prefix = block_prefix;

            temp_storage.warp_aggregates[linear_tid]    = downsweep_prefix;
        }

        CTA_SYNC();

        // Apply warp prefix to our lane's partial
        T outer_warp_exclusive = temp_storage.warp_aggregates[warp_id];
        inclusive_output = scan_op(outer_warp_exclusive, inclusive_output);
    }


};


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