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authorMiles Macklin <[email protected]>2017-03-10 14:51:31 +1300
committerMiles Macklin <[email protected]>2017-03-10 14:51:31 +1300
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tree4cc6f3288363889d7342f7f8407c0251e6904819 /external/cub-1.3.2/cub/block/block_scan.cuh
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+/******************************************************************************
+ * Copyright (c) 2011, Duane Merrill. All rights reserved.
+ * Copyright (c) 2011-2014, 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
+ * The cub::BlockScan class provides [<em>collective</em>](index.html#sec0) methods for computing a parallel prefix sum/scan of items partitioned across a CUDA thread block.
+ */
+
+#pragma once
+
+#include "specializations/block_scan_raking.cuh"
+#include "specializations/block_scan_warp_scans.cuh"
+#include "../util_arch.cuh"
+#include "../util_type.cuh"
+#include "../util_ptx.cuh"
+#include "../util_namespace.cuh"
+
+/// Optional outer namespace(s)
+CUB_NS_PREFIX
+
+/// CUB namespace
+namespace cub {
+
+
+
+/******************************************************************************
+ * Scan utility types
+ ******************************************************************************/
+
+#ifndef DOXYGEN_SHOULD_SKIP_THIS // Do not document
+
+/**
+ * Reduce-value-by-ID scan operator
+ */
+template <typename ReductionOp> ///< Wrapped reduction operator type
+struct ReduceByKeyOp
+{
+ ReductionOp op; ///< Wrapped reduction operator
+
+ /// Constructor
+ __device__ __forceinline__ ReduceByKeyOp(ReductionOp op) : op(op) {}
+
+ /// Scan operator
+ template <typename KeyValuePair>
+ __device__ __forceinline__ KeyValuePair operator()(
+ const KeyValuePair &first,
+ const KeyValuePair &second)
+ {
+ KeyValuePair retval;
+
+ retval.value = (second.key != first.key) ?
+ second.value : // The second value is for a different ID, return only that value
+ op(first.value, second.value); // The values are for the same ID so reduce them
+
+ retval.key = second.key;
+ return retval;
+ }
+};
+
+
+
+/**
+ * Segmented scan operator
+ */
+template <typename ReductionOp> ///< Wrapped reduction operator type
+struct SegmentedOp
+{
+ ReductionOp op; ///< Wrapped reduction operator
+
+ /// Constructor
+ __device__ __forceinline__ SegmentedOp(ReductionOp op) : op(op) {}
+
+ /// Scan operator
+ template <typename KeyValuePair>
+ __device__ __forceinline__ KeyValuePair operator()(
+ const KeyValuePair &first,
+ const KeyValuePair &second)
+ {
+ if (second.key) {
+ KeyValuePair retval;
+ retval.value = second.value;
+ retval.key = first.key + second.key;
+ return retval;
+ } else {
+ KeyValuePair retval;
+ retval.value = op(first.value, second.value);
+ retval.key = first.key + second.key;
+ return ;
+ }
+ }
+};
+
+#endif // DOXYGEN_SHOULD_SKIP_THIS
+
+
+
+/******************************************************************************
+ * Algorithmic variants
+ ******************************************************************************/
+
+/**
+ * \brief BlockScanAlgorithm enumerates alternative algorithms for cub::BlockScan to compute a parallel prefix scan across a CUDA thread block.
+ */
+enum BlockScanAlgorithm
+{
+
+ /**
+ * \par Overview
+ * An efficient "raking reduce-then-scan" prefix scan algorithm. Execution is comprised of five phases:
+ * -# Upsweep sequential reduction in registers (if threads contribute more than one input each). Each thread then places the partial reduction of its item(s) into shared memory.
+ * -# Upsweep sequential reduction in shared memory. Threads within a single warp rake across segments of shared partial reductions.
+ * -# A warp-synchronous Kogge-Stone style exclusive scan within the raking warp.
+ * -# Downsweep sequential exclusive scan in shared memory. Threads within a single warp rake across segments of shared partial reductions, seeded with the warp-scan output.
+ * -# Downsweep sequential scan in registers (if threads contribute more than one input), seeded with the raking scan output.
+ *
+ * \par
+ * \image html block_scan_raking.png
+ * <div class="centercaption">\p BLOCK_SCAN_RAKING data flow for a hypothetical 16-thread threadblock and 4-thread raking warp.</div>
+ *
+ * \par Performance Considerations
+ * - Although this variant may suffer longer turnaround latencies when the
+ * GPU is under-occupied, it can often provide higher overall throughput
+ * across the GPU when suitably occupied.
+ */
+ BLOCK_SCAN_RAKING,
+
+
+ /**
+ * \par Overview
+ * Similar to cub::BLOCK_SCAN_RAKING, but with fewer shared memory reads at
+ * the expense of higher register pressure. Raking threads preserve their
+ * "upsweep" segment of values in registers while performing warp-synchronous
+ * scan, allowing the "downsweep" not to re-read them from shared memory.
+ */
+ BLOCK_SCAN_RAKING_MEMOIZE,
+
+
+ /**
+ * \par Overview
+ * A quick "tiled warpscans" prefix scan algorithm. Execution is comprised of four phases:
+ * -# Upsweep sequential reduction in registers (if threads contribute more than one input each). Each thread then places the partial reduction of its item(s) into shared memory.
+ * -# Compute a shallow, but inefficient warp-synchronous Kogge-Stone style scan within each warp.
+ * -# A propagation phase where the warp scan outputs in each warp are updated with the aggregate from each preceding warp.
+ * -# Downsweep sequential scan in registers (if threads contribute more than one input), seeded with the raking scan output.
+ *
+ * \par
+ * \image html block_scan_warpscans.png
+ * <div class="centercaption">\p BLOCK_SCAN_WARP_SCANS data flow for a hypothetical 16-thread threadblock and 4-thread raking warp.</div>
+ *
+ * \par Performance Considerations
+ * - Although this variant may suffer lower overall throughput across the
+ * GPU because due to a heavy reliance on inefficient warpscans, it can
+ * often provide lower turnaround latencies when the GPU is under-occupied.
+ */
+ BLOCK_SCAN_WARP_SCANS,
+};
+
+
+/******************************************************************************
+ * Block scan
+ ******************************************************************************/
+
+/**
+ * \brief The BlockScan class provides [<em>collective</em>](index.html#sec0) methods for computing a parallel prefix sum/scan of items partitioned across a CUDA thread block. ![](block_scan_logo.png)
+ * \ingroup BlockModule
+ *
+ * \tparam T Data type being scanned
+ * \tparam BLOCK_DIM_X The thread block length in threads along the X dimension
+ * \tparam ALGORITHM <b>[optional]</b> cub::BlockScanAlgorithm enumerator specifying the underlying algorithm to use (default: cub::BLOCK_SCAN_RAKING)
+ * \tparam BLOCK_DIM_Y <b>[optional]</b> The thread block length in threads along the Y dimension (default: 1)
+ * \tparam BLOCK_DIM_Z <b>[optional]</b> The thread block length in threads along the Z dimension (default: 1)
+ * \tparam PTX_ARCH <b>[optional]</b> \ptxversion
+ *
+ * \par Overview
+ * - Given a list of input elements and a binary reduction operator, a [<em>prefix scan</em>](http://en.wikipedia.org/wiki/Prefix_sum)
+ * produces an output list where each element is computed to be the reduction
+ * of the elements occurring earlier in the input list. <em>Prefix sum</em>
+ * connotes a prefix scan with the addition operator. The term \em inclusive indicates
+ * that the <em>i</em><sup>th</sup> output reduction incorporates the <em>i</em><sup>th</sup> input.
+ * The term \em exclusive indicates the <em>i</em><sup>th</sup> input is not incorporated into
+ * the <em>i</em><sup>th</sup> output reduction.
+ * - \rowmajor
+ * - BlockScan can be optionally specialized by algorithm to accommodate different workload profiles:
+ * -# <b>cub::BLOCK_SCAN_RAKING</b>. An efficient (high throughput) "raking reduce-then-scan" prefix scan algorithm. [More...](\ref cub::BlockScanAlgorithm)
+ * -# <b>cub::BLOCK_SCAN_RAKING_MEMOIZE</b>. Similar to cub::BLOCK_SCAN_RAKING, but having higher throughput at the expense of additional register pressure for intermediate storage. [More...](\ref cub::BlockScanAlgorithm)
+ * -# <b>cub::BLOCK_SCAN_WARP_SCANS</b>. A quick (low latency) "tiled warpscans" prefix scan algorithm. [More...](\ref cub::BlockScanAlgorithm)
+ *
+ * \par Performance Considerations
+ * - \granularity
+ * - Uses special instructions when applicable (e.g., warp \p SHFL)
+ * - Uses synchronization-free communication between warp lanes when applicable
+ * - Invokes a minimal number of minimal block-wide synchronization barriers (only
+ * one or two depending on algorithm selection)
+ * - Incurs zero bank conflicts for most types
+ * - Computation is slightly more efficient (i.e., having lower instruction overhead) for:
+ * - Prefix sum variants (<b><em>vs.</em></b> generic scan)
+ * - \blocksize
+ * - See cub::BlockScanAlgorithm for performance details regarding algorithmic alternatives
+ *
+ * \par A Simple Example
+ * \blockcollective{BlockScan}
+ * \par
+ * The code snippet below illustrates an exclusive prefix sum of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix sum
+ * BlockScan(temp_storage).ExclusiveSum(thread_data, thread_data);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is
+ * <tt>{[1,1,1,1], [1,1,1,1], ..., [1,1,1,1]}</tt>.
+ * The corresponding output \p thread_data in those threads will be
+ * <tt>{[0,1,2,3], [4,5,6,7], ..., [508,509,510,511]}</tt>.
+ *
+ */
+template <
+ typename T,
+ int BLOCK_DIM_X,
+ BlockScanAlgorithm ALGORITHM = BLOCK_SCAN_RAKING,
+ int BLOCK_DIM_Y = 1,
+ int BLOCK_DIM_Z = 1,
+ int PTX_ARCH = CUB_PTX_ARCH>
+class BlockScan
+{
+private:
+
+ /******************************************************************************
+ * Constants and type definitions
+ ******************************************************************************/
+
+ /// Constants
+ enum
+ {
+ /// The thread block size in threads
+ BLOCK_THREADS = BLOCK_DIM_X * BLOCK_DIM_Y * BLOCK_DIM_Z,
+ };
+
+ /**
+ * Ensure the template parameterization meets the requirements of the
+ * specified algorithm. Currently, the BLOCK_SCAN_WARP_SCANS policy
+ * cannot be used with threadblock sizes not a multiple of the
+ * architectural warp size.
+ */
+ static const BlockScanAlgorithm SAFE_ALGORITHM =
+ ((ALGORITHM == BLOCK_SCAN_WARP_SCANS) && (BLOCK_THREADS % CUB_WARP_THREADS(PTX_ARCH) != 0)) ?
+ BLOCK_SCAN_RAKING :
+ ALGORITHM;
+
+ typedef BlockScanWarpScans<T, BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH> WarpScans;
+ typedef BlockScanRaking<T, BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z, (SAFE_ALGORITHM == BLOCK_SCAN_RAKING_MEMOIZE), PTX_ARCH> Raking;
+
+ /// Define the delegate type for the desired algorithm
+ typedef typename If<(SAFE_ALGORITHM == BLOCK_SCAN_WARP_SCANS),
+ WarpScans,
+ Raking>::Type InternalBlockScan;
+
+ /// Shared memory storage layout type for BlockScan
+ typedef typename InternalBlockScan::TempStorage _TempStorage;
+
+
+ /******************************************************************************
+ * Thread fields
+ ******************************************************************************/
+
+ /// Shared storage reference
+ _TempStorage &temp_storage;
+
+ /// Linear thread-id
+ int linear_tid;
+
+
+ /******************************************************************************
+ * Utility methods
+ ******************************************************************************/
+
+ /// Internal storage allocator
+ __device__ __forceinline__ _TempStorage& PrivateStorage()
+ {
+ __shared__ _TempStorage private_storage;
+ return private_storage;
+ }
+
+
+public:
+
+ /// \smemstorage{BlockScan}
+ struct TempStorage : Uninitialized<_TempStorage> {};
+
+
+ /******************************************************************//**
+ * \name Collective constructors
+ *********************************************************************/
+ //@{
+
+ /**
+ * \brief Collective constructor using a private static allocation of shared memory as temporary storage.
+ */
+ __device__ __forceinline__ BlockScan()
+ :
+ temp_storage(PrivateStorage()),
+ linear_tid(RowMajorTid(BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z))
+ {}
+
+
+ /**
+ * \brief Collective constructor using the specified memory allocation as temporary storage.
+ */
+ __device__ __forceinline__ BlockScan(
+ TempStorage &temp_storage) ///< [in] Reference to memory allocation having layout type TempStorage
+ :
+ temp_storage(temp_storage.Alias()),
+ linear_tid(RowMajorTid(BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z))
+ {}
+
+
+
+
+
+
+ //@} end member group
+ /******************************************************************//**
+ * \name Exclusive prefix sum operations
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes one input element.
+ *
+ * \par
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix sum of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix sum
+ * BlockScan(temp_storage).ExclusiveSum(thread_data, thread_data);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>1, 1, ..., 1</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>0, 1, ..., 127</tt>.
+ *
+ */
+ __device__ __forceinline__ void ExclusiveSum(
+ T input, ///< [in] Calling thread's input item
+ T &output) ///< [out] Calling thread's output item (may be aliased to \p input)
+ {
+ T block_aggregate;
+ InternalBlockScan(temp_storage).ExclusiveSum(input, output, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes one input element. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix sum of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage).ExclusiveSum(thread_data, thread_data, block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>1, 1, ..., 1</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>0, 1, ..., 127</tt>.
+ * Furthermore the value \p 128 will be stored in \p block_aggregate for all threads.
+ *
+ */
+ __device__ __forceinline__ void ExclusiveSum(
+ T input, ///< [in] Calling thread's input item
+ T &output, ///< [out] Calling thread's output item (may be aliased to \p input)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ InternalBlockScan(temp_storage).ExclusiveSum(input, output, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes one input element. Instead of using 0 as the block-wide prefix, 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an exclusive prefix sum over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 128 integer items that are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total += block_aggregate;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(0);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data = d_data[block_offset];
+ *
+ * // Collectively compute the block-wide exclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage).ExclusiveSum(
+ * thread_data, thread_data, block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * d_data[block_offset] = thread_data;
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>1, 1, 1, 1, 1, 1, 1, 1, ...</tt>.
+ * The corresponding output for the first segment will be <tt>0, 1, ..., 127</tt>.
+ * The output for the second segment will be <tt>128, 129, ..., 255</tt>. Furthermore,
+ * the value \p 128 will be stored in \p block_aggregate for all threads after each scan.
+ *
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void ExclusiveSum(
+ T input, ///< [in] Calling thread's input item
+ T &output, ///< [out] Calling thread's output item (may be aliased to \p input)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ InternalBlockScan(temp_storage).ExclusiveSum(input, output, block_aggregate, block_prefix_callback_op);
+ }
+
+
+ //@} end member group
+ /******************************************************************//**
+ * \name Exclusive prefix sum operations (multiple data per thread)
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes an array of consecutive input elements.
+ *
+ * \par
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix sum of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix sum
+ * BlockScan(temp_storage).ExclusiveSum(thread_data, thread_data);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>{ [1,1,1,1], [1,1,1,1], ..., [1,1,1,1] }</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>{ [0,1,2,3], [4,5,6,7], ..., [508,509,510,511] }</tt>.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ */
+ template <int ITEMS_PER_THREAD>
+ __device__ __forceinline__ void ExclusiveSum(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD]) ///< [out] Calling thread's output items (may be aliased to \p input)
+ {
+ // Reduce consecutive thread items in registers
+ Sum scan_op;
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveSum(thread_partial, thread_partial);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial);
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes an array of consecutive input elements. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix sum of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage).ExclusiveSum(thread_data, thread_data, block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>{ [1,1,1,1], [1,1,1,1], ..., [1,1,1,1] }</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>{ [0,1,2,3], [4,5,6,7], ..., [508,509,510,511] }</tt>.
+ * Furthermore the value \p 512 will be stored in \p block_aggregate for all threads.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ */
+ template <int ITEMS_PER_THREAD>
+ __device__ __forceinline__ void ExclusiveSum(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ // Reduce consecutive thread items in registers
+ Sum scan_op;
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveSum(thread_partial, thread_partial, block_aggregate);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial);
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes an array of consecutive input elements. Instead of using 0 as the block-wide prefix, 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an exclusive prefix sum over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 512 integer items that are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3)
+ * across 128 threads where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total += block_aggregate;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockLoad, BlockStore, and BlockScan for a 1D block of 128 threads, 4 ints per thread
+ * typedef cub::BlockLoad<int*, 128, 4, BLOCK_LOAD_TRANSPOSE> BlockLoad;
+ * typedef cub::BlockStore<int*, 128, 4, BLOCK_STORE_TRANSPOSE> BlockStore;
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate aliased shared memory for BlockLoad, BlockStore, and BlockScan
+ * __shared__ union {
+ * typename BlockLoad::TempStorage load;
+ * typename BlockScan::TempStorage scan;
+ * typename BlockStore::TempStorage store;
+ * } temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(0);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128 * 4)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * BlockLoad(temp_storage.load).Load(d_data + block_offset, thread_data);
+ * __syncthreads();
+ *
+ * // Collectively compute the block-wide exclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage.scan).ExclusiveSum(
+ * thread_data, thread_data, block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * BlockStore(temp_storage.store).Store(d_data + block_offset, thread_data);
+ * __syncthreads();
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>1, 1, 1, 1, 1, 1, 1, 1, ...</tt>.
+ * The corresponding output for the first segment will be <tt>0, 1, 2, 3, ..., 510, 511</tt>.
+ * The output for the second segment will be <tt>512, 513, 514, 515, ..., 1022, 1023</tt>. Furthermore,
+ * the value \p 512 will be stored in \p block_aggregate for all threads after each scan.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void ExclusiveSum(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ // Reduce consecutive thread items in registers
+ Sum scan_op;
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveSum(thread_partial, thread_partial, block_aggregate, block_prefix_callback_op);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial);
+ }
+
+
+
+ //@} end member group // Inclusive prefix sums
+ /******************************************************************//**
+ * \name Exclusive prefix scan operations
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes one input element.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix max scan of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix max scan
+ * BlockScan(temp_storage).ExclusiveScan(thread_data, thread_data, INT_MIN, cub::Max());
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>0, -1, 2, -3, ..., 126, -127</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>INT_MIN, 0, 0, 2, ..., 124, 126</tt>.
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ 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 to \p input)
+ T identity, ///< [in] Identity value
+ ScanOp scan_op) ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ {
+ T block_aggregate;
+ InternalBlockScan(temp_storage).ExclusiveScan(input, output, identity, scan_op, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an exclusive 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.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix max scan of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage).ExclusiveScan(thread_data, thread_data, INT_MIN, cub::Max(), block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>0, -1, 2, -3, ..., 126, -127</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>INT_MIN, 0, 0, 2, ..., 124, 126</tt>.
+ * Furthermore the value \p 126 will be stored in \p block_aggregate for all threads.
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <typename ScanOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T input, ///< [in] Calling thread's input items
+ T &output, ///< [out] Calling thread's output items (may be aliased to \p input)
+ T identity, ///< [in] Identity value
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ InternalBlockScan(temp_storage).ExclusiveScan(input, output, identity, scan_op, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an exclusive 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an exclusive prefix max scan over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 128 integer items that are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total = (block_aggregate > old_prefix) ? block_aggregate : old_prefix;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(INT_MIN);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data = d_data[block_offset];
+ *
+ * // Collectively compute the block-wide exclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage).ExclusiveScan(
+ * thread_data, thread_data, INT_MIN, cub::Max(), block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * d_data[block_offset] = thread_data;
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>0, -1, 2, -3, 4, -5, ...</tt>.
+ * The corresponding output for the first segment will be <tt>INT_MIN, 0, 0, 2, ..., 124, 126</tt>.
+ * The output for the second segment will be <tt>126, 128, 128, 130, ..., 252, 254</tt>. Furthermore,
+ * \p block_aggregate will be assigned \p 126 in all threads after the first scan, assigned \p 254 after the second
+ * scan, etc.
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ typename ScanOp,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T input, ///< [in] Calling thread's input item
+ T &output, ///< [out] Calling thread's output item (may be aliased to \p input)
+ T identity, ///< [in] Identity value
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ InternalBlockScan(temp_storage).ExclusiveScan(input, output, identity, scan_op, block_aggregate, block_prefix_callback_op);
+ }
+
+
+ //@} end member group // Inclusive prefix sums
+ /******************************************************************//**
+ * \name Exclusive prefix scan operations (multiple data per thread)
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix max scan of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix max scan
+ * BlockScan(temp_storage).ExclusiveScan(thread_data, thread_data, INT_MIN, cub::Max());
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is
+ * <tt>{ [0,-1,2,-3], [4,-5,6,-7], ..., [508,-509,510,-511] }</tt>.
+ * The corresponding output \p thread_data in those threads will be
+ * <tt>{ [INT_MIN,0,0,2], [2,4,4,6], ..., [506,508,508,510] }</tt>.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ T identity, ///< [in] Identity value
+ ScanOp scan_op) ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, identity, scan_op);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial);
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an exclusive prefix max scan of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide exclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage).ExclusiveScan(thread_data, thread_data, INT_MIN, cub::Max(), block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>{ [0,-1,2,-3], [4,-5,6,-7], ..., [508,-509,510,-511] }</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>{ [INT_MIN,0,0,2], [2,4,4,6], ..., [506,508,508,510] }</tt>.
+ * Furthermore the value \p 510 will be stored in \p block_aggregate for all threads.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ T identity, ///< [in] Identity value
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, identity, scan_op, block_aggregate);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial);
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements. 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an exclusive prefix max scan over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 128 integer items that are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total = (block_aggregate > old_prefix) ? block_aggregate : old_prefix;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockLoad, BlockStore, and BlockScan for a 1D block of 128 threads, 4 ints per thread
+ * typedef cub::BlockLoad<int*, 128, 4, BLOCK_LOAD_TRANSPOSE> BlockLoad;
+ * typedef cub::BlockStore<int*, 128, 4, BLOCK_STORE_TRANSPOSE> BlockStore;
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate aliased shared memory for BlockLoad, BlockStore, and BlockScan
+ * __shared__ union {
+ * typename BlockLoad::TempStorage load;
+ * typename BlockScan::TempStorage scan;
+ * typename BlockStore::TempStorage store;
+ * } temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(0);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128 * 4)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * BlockLoad(temp_storage.load).Load(d_data + block_offset, thread_data);
+ * __syncthreads();
+ *
+ * // Collectively compute the block-wide exclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage.scan).ExclusiveScan(
+ * thread_data, thread_data, INT_MIN, cub::Max(), block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * BlockStore(temp_storage.store).Store(d_data + block_offset, thread_data);
+ * __syncthreads();
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>0, -1, 2, -3, 4, -5, ...</tt>.
+ * The corresponding output for the first segment will be <tt>INT_MIN, 0, 0, 2, 2, 4, ..., 508, 510</tt>.
+ * The output for the second segment will be <tt>510, 512, 512, 514, 514, 516, ..., 1020, 1022</tt>. Furthermore,
+ * \p block_aggregate will be assigned \p 510 in all threads after the first scan, assigned \p 1022 after the second
+ * scan, etc.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ T identity, ///< [in] Identity value
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, identity, scan_op, block_aggregate, block_prefix_callback_op);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial);
+ }
+
+
+ //@} end member group
+
+#ifndef DOXYGEN_SHOULD_SKIP_THIS // Do not document
+
+ /******************************************************************//**
+ * \name Exclusive prefix scan operations (identityless, single datum per thread)
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes one input element. With no identity value, the output computed for <em>thread</em><sub>0</sub> is undefined.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ 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 to \p input)
+ ScanOp scan_op) ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ {
+ T block_aggregate;
+ InternalBlockScan(temp_storage).ExclusiveScan(input, output, scan_op, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an exclusive 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 identity value, the output computed for <em>thread</em><sub>0</sub> is undefined.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ 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 to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ InternalBlockScan(temp_storage).ExclusiveScan(input, output, scan_op, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an exclusive 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ typename ScanOp,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T input, ///< [in] Calling thread's input item
+ T &output, ///< [out] Calling thread's output item (may be aliased to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ InternalBlockScan(temp_storage).ExclusiveScan(input, output, scan_op, block_aggregate, block_prefix_callback_op);
+ }
+
+
+ //@} end member group
+ /******************************************************************//**
+ * \name Exclusive prefix scan operations (identityless, multiple data per thread)
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements. With no identity value, the output computed for <em>thread</em><sub>0</sub> is undefined.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ ScanOp scan_op) ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, scan_op);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial, (linear_tid != 0));
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements. Also provides every thread with the block-wide \p block_aggregate of all inputs. With no identity value, the output computed for <em>thread</em><sub>0</sub> is undefined.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, scan_op, block_aggregate);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial, (linear_tid != 0));
+ }
+
+
+ /**
+ * \brief Computes an exclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements. 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void ExclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, scan_op, block_aggregate, block_prefix_callback_op);
+
+ // Exclusive scan in registers with prefix
+ ThreadScanExclusive(input, output, scan_op, thread_partial);
+ }
+
+
+ //@} end member group
+
+#endif // DOXYGEN_SHOULD_SKIP_THIS
+
+ /******************************************************************//**
+ * \name Inclusive prefix sum operations
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes one input element.
+ *
+ * \par
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix sum of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix sum
+ * BlockScan(temp_storage).InclusiveSum(thread_data, thread_data);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>1, 1, ..., 1</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>1, 2, ..., 128</tt>.
+ *
+ */
+ __device__ __forceinline__ void InclusiveSum(
+ T input, ///< [in] Calling thread's input item
+ T &output) ///< [out] Calling thread's output item (may be aliased to \p input)
+ {
+ T block_aggregate;
+ InternalBlockScan(temp_storage).InclusiveSum(input, output, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes one input element. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix sum of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage).InclusiveSum(thread_data, thread_data, block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>1, 1, ..., 1</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>1, 2, ..., 128</tt>.
+ * Furthermore the value \p 128 will be stored in \p block_aggregate for all threads.
+ *
+ */
+ __device__ __forceinline__ void InclusiveSum(
+ T input, ///< [in] Calling thread's input item
+ T &output, ///< [out] Calling thread's output item (may be aliased to \p input)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ InternalBlockScan(temp_storage).InclusiveSum(input, output, block_aggregate);
+ }
+
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes one input element. Instead of using 0 as the block-wide prefix, 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an inclusive prefix sum over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 128 integer items that are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total += block_aggregate;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(0);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data = d_data[block_offset];
+ *
+ * // Collectively compute the block-wide inclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage).InclusiveSum(
+ * thread_data, thread_data, block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * d_data[block_offset] = thread_data;
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>1, 1, 1, 1, 1, 1, 1, 1, ...</tt>.
+ * The corresponding output for the first segment will be <tt>1, 2, ..., 128</tt>.
+ * The output for the second segment will be <tt>129, 130, ..., 256</tt>. Furthermore,
+ * the value \p 128 will be stored in \p block_aggregate for all threads after each scan.
+ *
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void InclusiveSum(
+ T input, ///< [in] Calling thread's input item
+ T &output, ///< [out] Calling thread's output item (may be aliased to \p input)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ InternalBlockScan(temp_storage).InclusiveSum(input, output, block_aggregate, block_prefix_callback_op);
+ }
+
+
+ //@} end member group
+ /******************************************************************//**
+ * \name Inclusive prefix sum operations (multiple data per thread)
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes an array of consecutive input elements.
+ *
+ * \par
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix sum of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix sum
+ * BlockScan(temp_storage).InclusiveSum(thread_data, thread_data);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>{ [1,1,1,1], [1,1,1,1], ..., [1,1,1,1] }</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>{ [1,2,3,4], [5,6,7,8], ..., [509,510,511,512] }</tt>.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ */
+ template <int ITEMS_PER_THREAD>
+ __device__ __forceinline__ void InclusiveSum(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD]) ///< [out] Calling thread's output items (may be aliased to \p input)
+ {
+ if (ITEMS_PER_THREAD == 1)
+ {
+ InclusiveSum(input[0], output[0]);
+ }
+ else
+ {
+ // Reduce consecutive thread items in registers
+ Sum scan_op;
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveSum(thread_partial, thread_partial);
+
+ // Inclusive scan in registers with prefix
+ ThreadScanInclusive(input, output, scan_op, thread_partial, (linear_tid != 0));
+ }
+ }
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes an array of consecutive input elements. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix sum of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage).InclusiveSum(thread_data, thread_data, block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is
+ * <tt>{ [1,1,1,1], [1,1,1,1], ..., [1,1,1,1] }</tt>. The
+ * corresponding output \p thread_data in those threads will be
+ * <tt>{ [1,2,3,4], [5,6,7,8], ..., [509,510,511,512] }</tt>.
+ * Furthermore the value \p 512 will be stored in \p block_aggregate for all threads.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <int ITEMS_PER_THREAD>
+ __device__ __forceinline__ void InclusiveSum(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ if (ITEMS_PER_THREAD == 1)
+ {
+ InclusiveSum(input[0], output[0], block_aggregate);
+ }
+ else
+ {
+ // Reduce consecutive thread items in registers
+ Sum scan_op;
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveSum(thread_partial, thread_partial, block_aggregate);
+
+ // Inclusive scan in registers with prefix
+ ThreadScanInclusive(input, output, scan_op, thread_partial, (linear_tid != 0));
+ }
+ }
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using addition (+) as the scan operator. Each thread contributes an array of consecutive input elements. Instead of using 0 as the block-wide prefix, 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an inclusive prefix sum over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 512 integer items that are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3)
+ * across 128 threads where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total += block_aggregate;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockLoad, BlockStore, and BlockScan for a 1D block of 128 threads, 4 ints per thread
+ * typedef cub::BlockLoad<int*, 128, 4, BLOCK_LOAD_TRANSPOSE> BlockLoad;
+ * typedef cub::BlockStore<int*, 128, 4, BLOCK_STORE_TRANSPOSE> BlockStore;
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate aliased shared memory for BlockLoad, BlockStore, and BlockScan
+ * __shared__ union {
+ * typename BlockLoad::TempStorage load;
+ * typename BlockScan::TempStorage scan;
+ * typename BlockStore::TempStorage store;
+ * } temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(0);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128 * 4)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * BlockLoad(temp_storage.load).Load(d_data + block_offset, thread_data);
+ * __syncthreads();
+ *
+ * // Collectively compute the block-wide inclusive prefix sum
+ * int block_aggregate;
+ * BlockScan(temp_storage.scan).IncluisveSum(
+ * thread_data, thread_data, block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * BlockStore(temp_storage.store).Store(d_data + block_offset, thread_data);
+ * __syncthreads();
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>1, 1, 1, 1, 1, 1, 1, 1, ...</tt>.
+ * The corresponding output for the first segment will be <tt>1, 2, 3, 4, ..., 511, 512</tt>.
+ * The output for the second segment will be <tt>513, 514, 515, 516, ..., 1023, 1024</tt>. Furthermore,
+ * the value \p 512 will be stored in \p block_aggregate for all threads after each scan.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void InclusiveSum(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ if (ITEMS_PER_THREAD == 1)
+ {
+ InclusiveSum(input[0], output[0], block_aggregate, block_prefix_callback_op);
+ }
+ else
+ {
+ // Reduce consecutive thread items in registers
+ Sum scan_op;
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveSum(thread_partial, thread_partial, block_aggregate, block_prefix_callback_op);
+
+ // Inclusive scan in registers with prefix
+ ThreadScanInclusive(input, output, scan_op, thread_partial);
+ }
+ }
+
+
+ //@} end member group
+ /******************************************************************//**
+ * \name Inclusive prefix scan operations
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes one input element.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix max scan of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix max scan
+ * BlockScan(temp_storage).InclusiveScan(thread_data, thread_data, cub::Max());
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>0, -1, 2, -3, ..., 126, -127</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>0, 0, 2, 2, ..., 126, 126</tt>.
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ 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 to \p input)
+ ScanOp scan_op) ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ {
+ T block_aggregate;
+ InclusiveScan(input, output, scan_op, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an inclusive 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.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix max scan of 128 integer items that
+ * are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain input item for each thread
+ * int thread_data;
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage).InclusiveScan(thread_data, thread_data, cub::Max(), block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>0, -1, 2, -3, ..., 126, -127</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>0, 0, 2, 2, ..., 126, 126</tt>.
+ * Furthermore the value \p 126 will be stored in \p block_aggregate for all threads.
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ 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 to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ InternalBlockScan(temp_storage).InclusiveScan(input, output, scan_op, block_aggregate);
+ }
+
+
+ /**
+ * \brief Computes an inclusive 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - Supports non-commutative scan operators.
+ * - \rowmajor
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an inclusive prefix max scan over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 128 integer items that are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total = (block_aggregate > old_prefix) ? block_aggregate : old_prefix;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(INT_MIN);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data = d_data[block_offset];
+ *
+ * // Collectively compute the block-wide inclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage).InclusiveScan(
+ * thread_data, thread_data, cub::Max(), block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * d_data[block_offset] = thread_data;
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>0, -1, 2, -3, 4, -5, ...</tt>.
+ * The corresponding output for the first segment will be <tt>0, 0, 2, 2, ..., 126, 126</tt>.
+ * The output for the second segment will be <tt>128, 128, 130, 130, ..., 254, 254</tt>. Furthermore,
+ * \p block_aggregate will be assigned \p 126 in all threads after the first scan, assigned \p 254 after the second
+ * scan, etc.
+ *
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ typename ScanOp,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void InclusiveScan(
+ T input, ///< [in] Calling thread's input item
+ T &output, ///< [out] Calling thread's output item (may be aliased to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ InternalBlockScan(temp_storage).InclusiveScan(input, output, scan_op, block_aggregate, block_prefix_callback_op);
+ }
+
+
+ //@} end member group
+ /******************************************************************//**
+ * \name Inclusive prefix scan operations (multiple data per thread)
+ *********************************************************************/
+ //@{
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix max scan of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix max scan
+ * BlockScan(temp_storage).InclusiveScan(thread_data, thread_data, cub::Max());
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is <tt>{ [0,-1,2,-3], [4,-5,6,-7], ..., [508,-509,510,-511] }</tt>. The
+ * corresponding output \p thread_data in those threads will be <tt>{ [0,0,2,2], [4,4,6,6], ..., [508,508,510,510] }</tt>.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp>
+ __device__ __forceinline__ void InclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ ScanOp scan_op) ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ {
+ if (ITEMS_PER_THREAD == 1)
+ {
+ InclusiveScan(input[0], output[0], scan_op);
+ }
+ else
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, scan_op);
+
+ // Inclusive scan in registers with prefix
+ ThreadScanInclusive(input, output, scan_op, thread_partial, (linear_tid != 0));
+ }
+ }
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates an inclusive prefix max scan of 512 integer items that
+ * are partitioned in a [<em>blocked arrangement</em>](index.html#sec5sec3) across 128 threads
+ * where each thread owns 4 consecutive items.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * __global__ void ExampleKernel(...)
+ * {
+ * // Specialize BlockScan for a 1D block of 128 threads on type int
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate shared memory for BlockScan
+ * __shared__ typename BlockScan::TempStorage temp_storage;
+ *
+ * // Obtain a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * ...
+ *
+ * // Collectively compute the block-wide inclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage).InclusiveScan(thread_data, thread_data, cub::Max(), block_aggregate);
+ *
+ * \endcode
+ * \par
+ * Suppose the set of input \p thread_data across the block of threads is
+ * <tt>{ [0,-1,2,-3], [4,-5,6,-7], ..., [508,-509,510,-511] }</tt>.
+ * The corresponding output \p thread_data in those threads will be
+ * <tt>{ [0,0,2,2], [4,4,6,6], ..., [508,508,510,510] }</tt>.
+ * Furthermore the value \p 510 will be stored in \p block_aggregate for all threads.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp>
+ __device__ __forceinline__ void InclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate) ///< [out] block-wide aggregate reduction of input items
+ {
+ if (ITEMS_PER_THREAD == 1)
+ {
+ InclusiveScan(input[0], output[0], scan_op, block_aggregate);
+ }
+ else
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, scan_op, block_aggregate);
+
+ // Inclusive scan in registers with prefix
+ ThreadScanInclusive(input, output, scan_op, thread_partial, (linear_tid != 0));
+ }
+ }
+
+
+ /**
+ * \brief Computes an inclusive block-wide prefix scan using the specified binary \p scan_op functor. Each thread contributes an array of consecutive input elements. 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 threadblock's scan inputs. Also provides every thread with the block-wide \p block_aggregate of all inputs.
+ *
+ * \par
+ * - The \p block_prefix_callback_op functor must implement a member function <tt>T operator()(T block_aggregate)</tt>.
+ * The functor's input parameter \p block_aggregate is the same value also returned by the scan operation.
+ * The functor will be invoked by the first warp of threads in the block, however only the return value from
+ * <em>lane</em><sub>0</sub> is applied as the block-wide prefix. Can be stateful.
+ * - Supports non-commutative scan operators.
+ * - \blocked
+ * - \granularity
+ * - \smemreuse
+ *
+ * \par Snippet
+ * The code snippet below illustrates a single thread block that progressively
+ * computes an inclusive prefix max scan over multiple "tiles" of input using a
+ * prefix functor to maintain a running total between block-wide scans. Each tile consists
+ * of 128 integer items that are partitioned across 128 threads.
+ * \par
+ * \code
+ * #include <cub/cub.cuh> // or equivalently <cub/block/block_scan.cuh>
+ *
+ * // A stateful callback functor that maintains a running prefix to be applied
+ * // during consecutive scan operations.
+ * struct BlockPrefixCallbackOp
+ * {
+ * // Running prefix
+ * int running_total;
+ *
+ * // Constructor
+ * __device__ BlockPrefixCallbackOp(int running_total) : running_total(running_total) {}
+ *
+ * // Callback operator to be entered by the first warp of threads in the block.
+ * // Thread-0 is responsible for returning a value for seeding the block-wide scan.
+ * __device__ int operator()(int block_aggregate)
+ * {
+ * int old_prefix = running_total;
+ * running_total = (block_aggregate > old_prefix) ? block_aggregate : old_prefix;
+ * return old_prefix;
+ * }
+ * };
+ *
+ * __global__ void ExampleKernel(int *d_data, int num_items, ...)
+ * {
+ * // Specialize BlockLoad, BlockStore, and BlockScan for a 1D block of 128 threads, 4 ints per thread
+ * typedef cub::BlockLoad<int*, 128, 4, BLOCK_LOAD_TRANSPOSE> BlockLoad;
+ * typedef cub::BlockStore<int*, 128, 4, BLOCK_STORE_TRANSPOSE> BlockStore;
+ * typedef cub::BlockScan<int, 128> BlockScan;
+ *
+ * // Allocate aliased shared memory for BlockLoad, BlockStore, and BlockScan
+ * __shared__ union {
+ * typename BlockLoad::TempStorage load;
+ * typename BlockScan::TempStorage scan;
+ * typename BlockStore::TempStorage store;
+ * } temp_storage;
+ *
+ * // Initialize running total
+ * BlockPrefixCallbackOp prefix_op(0);
+ *
+ * // Have the block iterate over segments of items
+ * for (int block_offset = 0; block_offset < num_items; block_offset += 128 * 4)
+ * {
+ * // Load a segment of consecutive items that are blocked across threads
+ * int thread_data[4];
+ * BlockLoad(temp_storage.load).Load(d_data + block_offset, thread_data);
+ * __syncthreads();
+ *
+ * // Collectively compute the block-wide inclusive prefix max scan
+ * int block_aggregate;
+ * BlockScan(temp_storage.scan).InclusiveScan(
+ * thread_data, thread_data, cub::Max(), block_aggregate, prefix_op);
+ * __syncthreads();
+ *
+ * // Store scanned items to output segment
+ * BlockStore(temp_storage.store).Store(d_data + block_offset, thread_data);
+ * __syncthreads();
+ * }
+ * \endcode
+ * \par
+ * Suppose the input \p d_data is <tt>0, -1, 2, -3, 4, -5, ...</tt>.
+ * The corresponding output for the first segment will be <tt>0, 0, 2, 2, 4, 4, ..., 510, 510</tt>.
+ * The output for the second segment will be <tt>512, 512, 514, 514, 516, 516, ..., 1022, 1022</tt>. Furthermore,
+ * \p block_aggregate will be assigned \p 510 in all threads after the first scan, assigned \p 1022 after the second
+ * scan, etc.
+ *
+ * \tparam ITEMS_PER_THREAD <b>[inferred]</b> The number of consecutive items partitioned onto each thread.
+ * \tparam ScanOp <b>[inferred]</b> Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.) type having member <tt>T operator()(const T &a, const T &b)</tt>
+ * \tparam BlockPrefixCallbackOp <b>[inferred]</b> Call-back functor type having member <tt>T operator()(T block_aggregate)</tt>
+ */
+ template <
+ int ITEMS_PER_THREAD,
+ typename ScanOp,
+ typename BlockPrefixCallbackOp>
+ __device__ __forceinline__ void InclusiveScan(
+ T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
+ T (&output)[ITEMS_PER_THREAD], ///< [out] Calling thread's output items (may be aliased to \p input)
+ ScanOp scan_op, ///< [in] Binary scan functor (e.g., an instance of cub::Sum, cub::Min, cub::Max, etc.)
+ T &block_aggregate, ///< [out] block-wide aggregate reduction of input items (exclusive of the \p block_prefix_callback_op value)
+ BlockPrefixCallbackOp &block_prefix_callback_op) ///< [in-out] <b>[<em>warp</em><sub>0</sub> only]</b> Call-back functor for specifying a block-wide prefix to be applied to all inputs.
+ {
+ if (ITEMS_PER_THREAD == 1)
+ {
+ InclusiveScan(input[0], output[0], scan_op, block_aggregate, block_prefix_callback_op);
+ }
+ else
+ {
+ // Reduce consecutive thread items in registers
+ T thread_partial = ThreadReduce(input, scan_op);
+
+ // Exclusive threadblock-scan
+ ExclusiveScan(thread_partial, thread_partial, scan_op, block_aggregate, block_prefix_callback_op);
+
+ // Inclusive scan in registers with prefix
+ ThreadScanInclusive(input, output, scan_op, thread_partial);
+ }
+ }
+
+ //@} end member group
+
+
+};
+
+/**
+ * \example example_block_scan.cu
+ */
+
+} // CUB namespace
+CUB_NS_POSTFIX // Optional outer namespace(s)
+