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/******************************************************************************
* Copyright (c) 2011, Duane Merrill. All rights reserved.
* Copyright (c) 2011-2018, NVIDIA CORPORATION. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* 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.
* * 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;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
******************************************************************************/
/**
* \file
* cub::BlockScanWarpscans provides warpscan-based variants of parallel prefix scan across a CUDA thread block.
*/
#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 thread block.
*/
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
{
/// The thread block size in threads
BLOCK_THREADS = BLOCK_DIM_X * BLOCK_DIM_Y * BLOCK_DIM_Z,
/// Number of warp threads
INNER_WARP_THREADS = CUB_WARP_THREADS(PTX_ARCH),
OUTER_WARP_THREADS = BLOCK_THREADS / INNER_WARP_THREADS,
/// Number of outer scan warps
OUTER_WARPS = INNER_WARP_THREADS
};
/// Outer WarpScan utility type
typedef WarpScan<T, OUTER_WARP_THREADS, PTX_ARCH> OuterWarpScanT;
/// Inner WarpScan utility type
typedef WarpScan<T, INNER_WARP_THREADS, PTX_ARCH> InnerWarpScanT;
typedef typename OuterWarpScanT::TempStorage OuterScanArray[OUTER_WARPS];
/// Shared memory storage layout type
struct _TempStorage
{
union Aliasable
{
Uninitialized<OuterScanArray> outer_warp_scan; ///< Buffer for warp-synchronous outer scans
typename InnerWarpScanT::TempStorage inner_warp_scan; ///< Buffer for warp-synchronous inner scan
} aliasable;
T warp_aggregates[OUTER_WARPS];
T block_aggregate; ///< Shared prefix for the entire thread block
};
/// 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((OUTER_WARPS == 1) ? 0 : linear_tid / OUTER_WARP_THREADS),
lane_id((OUTER_WARPS == 1) ? linear_tid : linear_tid % OUTER_WARP_THREADS)
{}
//---------------------------------------------------------------------
// Exclusive scans
//---------------------------------------------------------------------
/// 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.
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input item
T &exclusive_output, ///< [out] Calling thread's output item (may be aliased to \p input)
ScanOp scan_op) ///< [in] Binary scan operator
{
// Compute block-wide exclusive scan. The exclusive output from tid0 is invalid.
T block_aggregate;
ExclusiveScan(input, exclusive_output, scan_op, block_aggregate);
}
/// Computes an exclusive thread block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes one input element.
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input items
T &exclusive_output, ///< [out] Calling thread's output items (may be aliased to \p input)
const T &initial_value, ///< [in] Initial value to seed the exclusive scan
ScanOp scan_op) ///< [in] Binary scan operator
{
T block_aggregate;
ExclusiveScan(input, exclusive_output, initial_value, scan_op, block_aggregate);
}
/// 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.
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input item
T &exclusive_output, ///< [out] Calling thread's output item (may be aliased to \p input)
ScanOp scan_op, ///< [in] Binary scan operator
T &block_aggregate) ///< [out] Threadblock-wide aggregate reduction of input items
{
// 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;
}
}
/// 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.
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input items
T &exclusive_output, ///< [out] Calling thread's output items (may be aliased to \p input)
const T &initial_value, ///< [in] Initial value to seed the exclusive scan
ScanOp scan_op, ///< [in] Binary scan operator
T &block_aggregate) ///< [out] Threadblock-wide aggregate reduction of input items
{
// 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;
}
/// 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.
template <
typename ScanOp,
typename BlockPrefixCallbackOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input item
T &exclusive_output, ///< [out] Calling thread's output item (may be aliased to \p input)
ScanOp scan_op, ///< [in] Binary scan operator
BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <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.
{
// 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
//---------------------------------------------------------------------
/// Computes an inclusive thread block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes one input element.
template <typename ScanOp>
__device__ __forceinline__ void InclusiveScan(
T input, ///< [in] Calling thread's input item
T &inclusive_output, ///< [out] Calling thread's output item (may be aliased to \p input)
ScanOp scan_op) ///< [in] Binary scan operator
{
T block_aggregate;
InclusiveScan(input, inclusive_output, scan_op, block_aggregate);
}
/// 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.
template <typename ScanOp>
__device__ __forceinline__ void InclusiveScan(
T input, ///< [in] Calling thread's input item
T &inclusive_output, ///< [out] Calling thread's output item (may be aliased to \p input)
ScanOp scan_op, ///< [in] Binary scan operator
T &block_aggregate) ///< [out] Threadblock-wide aggregate reduction of input items
{
// 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);
}
}
/// 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.
template <
typename ScanOp,
typename BlockPrefixCallbackOp>
__device__ __forceinline__ void InclusiveScan(
T input, ///< [in] Calling thread's input item
T &inclusive_output, ///< [out] Calling thread's output item (may be aliased to \p input)
ScanOp scan_op, ///< [in] Binary scan operator
BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <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.
{
// 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)
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