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warp_scan_shfl.cuh
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/******************************************************************************
* Copyright (c) 2011, Duane Merrill. All rights reserved.
* Copyright (c) 2011-2013, 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::WarpScanShfl provides SHFL-based variants of parallel prefix scan across CUDA warps.
*/
#pragma once
#include "../../thread/thread_operators.cuh"
#include "../../util_type.cuh"
#include "../../util_ptx.cuh"
#include "../../util_namespace.cuh"
/// Optional outer namespace(s)
CUB_NS_PREFIX
/// CUB namespace
namespace cub {
/**
* \brief WarpScanShfl provides SHFL-based variants of parallel prefix scan across CUDA warps.
*/
template <
typename T, ///< Data type being scanned
int LOGICAL_WARPS, ///< Number of logical warps entrant
int LOGICAL_WARP_THREADS> ///< Number of threads per logical warp
struct WarpScanShfl
{
/******************************************************************************
* Constants and typedefs
******************************************************************************/
enum
{
/// The number of warp scan steps
STEPS = Log2<LOGICAL_WARP_THREADS>::VALUE,
// The 5-bit SHFL mask for logically splitting warps into sub-segments starts 8-bits up
SHFL_C = ((-1 << STEPS) & 31) << 8,
};
/// Shared memory storage layout type
typedef NullType TempStorage;
/******************************************************************************
* Thread fields
******************************************************************************/
int warp_id;
int lane_id;
/******************************************************************************
* Construction
******************************************************************************/
/// Constructor
__device__ __forceinline__ WarpScanShfl(
TempStorage &temp_storage,
int warp_id,
int lane_id)
:
warp_id(warp_id),
lane_id(lane_id)
{}
/******************************************************************************
* Operation
******************************************************************************/
/// Broadcast
__device__ __forceinline__ T Broadcast(
T input, ///< [in] The value to broadcast
int src_lane) ///< [in] Which warp lane is to do the broadcasting
{
typedef typename WordAlignment<T>::ShuffleWord ShuffleWord;
const int WORDS = (sizeof(T) + sizeof(ShuffleWord) - 1) / sizeof(ShuffleWord);
T output;
ShuffleWord *output_alias = reinterpret_cast<ShuffleWord *>(&output);
ShuffleWord *input_alias = reinterpret_cast<ShuffleWord *>(&input);
#pragma unroll
for (int WORD = 0; WORD < WORDS; ++WORD)
{
unsigned int shuffle_word = input_alias[WORD];
asm("shfl.idx.b32 %0, %1, %2, %3;"
: "=r"(shuffle_word) : "r"(shuffle_word), "r"(src_lane), "r"(LOGICAL_WARP_THREADS - 1));
output_alias[WORD] = (ShuffleWord) shuffle_word;
}
return output;
}
//---------------------------------------------------------------------
// Inclusive operations
//---------------------------------------------------------------------
/// Inclusive prefix sum with aggregate (single-SHFL)
__device__ __forceinline__ void InclusiveSum(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
T &warp_aggregate, ///< [out] Warp-wide aggregate reduction of input items.
Int2Type<true> single_shfl)
{
unsigned int temp = reinterpret_cast<unsigned int &>(input);
// Iterate scan steps
#pragma unroll
for (int STEP = 0; STEP < STEPS; STEP++)
{
// Use predicate set from SHFL to guard against invalid peers
asm(
"{"
" .reg .u32 r0;"
" .reg .pred p;"
" shfl.up.b32 r0|p, %1, %2, %3;"
" @p add.u32 r0, r0, %4;"
" mov.u32 %0, r0;"
"}"
: "=r"(temp) : "r"(temp), "r"(1 << STEP), "r"(SHFL_C), "r"(temp));
}
output = temp;
// Grab aggregate from last warp lane
warp_aggregate = Broadcast(output, LOGICAL_WARP_THREADS - 1);
}
/// Inclusive prefix sum with aggregate (multi-SHFL)
__device__ __forceinline__ void InclusiveSum(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
T &warp_aggregate, ///< [out] Warp-wide aggregate reduction of input items.
Int2Type<false> single_shfl) ///< [in] Marker type indicating whether only one SHFL instruction is required
{
// Delegate to generic scan
InclusiveScan(input, output, Sum(), warp_aggregate);
}
/// Inclusive prefix sum with aggregate (specialized for float)
__device__ __forceinline__ void InclusiveSum(
float input, ///< [in] Calling thread's input item.
float &output, ///< [out] Calling thread's output item. May be aliased with \p input.
float &warp_aggregate) ///< [out] Warp-wide aggregate reduction of input items.
{
output = input;
// Iterate scan steps
#pragma unroll
for (int STEP = 0; STEP < STEPS; STEP++)
{
// Use predicate set from SHFL to guard against invalid peers
asm(
"{"
" .reg .f32 r0;"
" .reg .pred p;"
" shfl.up.b32 r0|p, %1, %2, %3;"
" @p add.f32 r0, r0, %4;"
" mov.f32 %0, r0;"
"}"
: "=f"(output) : "f"(output), "r"(1 << STEP), "r"(SHFL_C), "f"(output));
}
// Grab aggregate from last warp lane
warp_aggregate = Broadcast(output, LOGICAL_WARP_THREADS - 1);
}
/// Inclusive prefix sum with aggregate (specialized for unsigned long long)
__device__ __forceinline__ void InclusiveSum(
unsigned long long input, ///< [in] Calling thread's input item.
unsigned long long &output, ///< [out] Calling thread's output item. May be aliased with \p input.
unsigned long long &warp_aggregate) ///< [out] Warp-wide aggregate reduction of input items.
{
output = input;
// Iterate scan steps
#pragma unroll
for (int STEP = 0; STEP < STEPS; STEP++)
{
// Use predicate set from SHFL to guard against invalid peers
asm(
"{"
" .reg .u32 r0;"
" .reg .u32 r1;"
" .reg .u32 lo;"
" .reg .u32 hi;"
" .reg .pred p;"
" mov.b64 {lo, hi}, %1;"
" shfl.up.b32 r0|p, lo, %2, %3;"
" shfl.up.b32 r1|p, hi, %2, %3;"
" @p add.cc.u32 r0, r0, lo;"
" @p addc.u32 r1, r1, hi;"
" mov.b64 %0, {r0, r1};"
"}"
: "=l"(output) : "l"(output), "r"(1 << STEP), "r"(SHFL_C));
}
// Grab aggregate from last warp lane
warp_aggregate = Broadcast(output, LOGICAL_WARP_THREADS - 1);
}
/// Inclusive prefix sum with aggregate (generic)
template <typename _T>
__device__ __forceinline__ void InclusiveSum(
_T input, ///< [in] Calling thread's input item.
_T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
_T &warp_aggregate) ///< [out] Warp-wide aggregate reduction of input items.
{
// Whether sharing can be done with a single SHFL instruction (vs multiple SFHL instructions)
Int2Type<(Traits<_T>::PRIMITIVE) && (sizeof(_T) <= sizeof(unsigned int))> single_shfl;
InclusiveSum(input, output, warp_aggregate, single_shfl);
}
/// Inclusive prefix sum
__device__ __forceinline__ void InclusiveSum(
T input, ///< [in] Calling thread's input item.
T &output) ///< [out] Calling thread's output item. May be aliased with \p input.
{
T warp_aggregate;
InclusiveSum(input, output, warp_aggregate);
}
/// Inclusive scan with aggregate
template <typename ScanOp>
__device__ __forceinline__ void InclusiveScan(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
ScanOp scan_op, ///< [in] Binary scan operator
T &warp_aggregate) ///< [out] Warp-wide aggregate reduction of input items.
{
output = input;
// Iterate scan steps
#pragma unroll
for (int STEP = 0; STEP < STEPS; STEP++)
{
// Grab addend from peer
const int OFFSET = 1 << STEP;
T temp = ShuffleUp(output, OFFSET);
// Perform scan op if from a valid peer
if (lane_id >= OFFSET)
output = scan_op(temp, output);
}
// Grab aggregate from last warp lane
warp_aggregate = Broadcast(output, LOGICAL_WARP_THREADS - 1);
}
/// Inclusive scan
template <typename ScanOp>
__device__ __forceinline__ void InclusiveScan(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
ScanOp scan_op) ///< [in] Binary scan operator
{
T warp_aggregate;
InclusiveScan(input, output, scan_op, warp_aggregate);
}
//---------------------------------------------------------------------
// Exclusive operations
//---------------------------------------------------------------------
/// Exclusive scan with aggregate
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
T identity, ///< [in] Identity value
ScanOp scan_op, ///< [in] Binary scan operator
T &warp_aggregate) ///< [out] Warp-wide aggregate reduction of input items.
{
// Compute inclusive scan
T inclusive;
InclusiveScan(input, inclusive, scan_op, warp_aggregate);
// Grab result from predecessor
T exclusive = ShuffleUp(inclusive, 1);
output = (lane_id == 0) ?
identity :
exclusive;
}
/// Exclusive scan
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
T identity, ///< [in] Identity value
ScanOp scan_op) ///< [in] Binary scan operator
{
T warp_aggregate;
ExclusiveScan(input, output, identity, scan_op, warp_aggregate);
}
/// Exclusive scan with aggregate, without identity
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
ScanOp scan_op, ///< [in] Binary scan operator
T &warp_aggregate) ///< [out] Warp-wide aggregate reduction of input items.
{
// Compute inclusive scan
T inclusive;
InclusiveScan(input, inclusive, scan_op, warp_aggregate);
// Grab result from predecessor
output = ShuffleUp(inclusive, 1);
}
/// Exclusive scan without identity
template <typename ScanOp>
__device__ __forceinline__ void ExclusiveScan(
T input, ///< [in] Calling thread's input item.
T &output, ///< [out] Calling thread's output item. May be aliased with \p input.
ScanOp scan_op) ///< [in] Binary scan operator
{
T warp_aggregate;
ExclusiveScan(input, output, scan_op, warp_aggregate);
}
};
} // CUB namespace
CUB_NS_POSTFIX // Optional outer namespace(s)
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