/******************************************************************************
* Copyright (c) 2011, Duane Merrill. All rights reserved.
* Copyright (c) 2011-2018, NVIDIA CORPORATION. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
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* notice, this list of conditions and the following disclaimer.
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* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
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* 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
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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/**
* \file
* The cub::BlockDiscontinuity class provides [collective](index.html#sec0) methods for flagging discontinuities within an ordered set of items partitioned across a CUDA thread block.
*/
#pragma once
#include "../util_type.cuh"
#include "../util_ptx.cuh"
#include "../util_namespace.cuh"
/// Optional outer namespace(s)
CUB_NS_PREFIX
/// CUB namespace
namespace cub {
/**
* \brief The BlockDiscontinuity class provides [collective](index.html#sec0) methods for flagging discontinuities within an ordered set of items partitioned across a CUDA thread block. 
* \ingroup BlockModule
*
* \tparam T The data type to be flagged.
* \tparam BLOCK_DIM_X The thread block length in threads along the X dimension
* \tparam BLOCK_DIM_Y [optional] The thread block length in threads along the Y dimension (default: 1)
* \tparam BLOCK_DIM_Z [optional] The thread block length in threads along the Z dimension (default: 1)
* \tparam PTX_ARCH [optional] \ptxversion
*
* \par Overview
* - A set of "head flags" (or "tail flags") is often used to indicate corresponding items
* that differ from their predecessors (or successors). For example, head flags are convenient
* for demarcating disjoint data segments as part of a segmented scan or reduction.
* - \blocked
*
* \par Performance Considerations
* - \granularity
*
* \par A Simple Example
* \blockcollective{BlockDiscontinuity}
* \par
* The code snippet below illustrates the head flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Collectively compute head flags for discontinuities in the segment
* int head_flags[4];
* BlockDiscontinuity(temp_storage).FlagHeads(head_flags, thread_data, cub::Inequality());
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], [3,4,4,4], ... }.
* The corresponding output \p head_flags in those threads will be
* { [1,0,1,0], [0,0,0,0], [1,1,0,0], [0,1,0,0], ... }.
*
* \par Performance Considerations
* - Incurs zero bank conflicts for most types
*
*/
template <
typename T,
int BLOCK_DIM_X,
int BLOCK_DIM_Y = 1,
int BLOCK_DIM_Z = 1,
int PTX_ARCH = CUB_PTX_ARCH>
class BlockDiscontinuity
{
private:
/******************************************************************************
* Constants and type definitions
******************************************************************************/
/// Constants
enum
{
/// The thread block size in threads
BLOCK_THREADS = BLOCK_DIM_X * BLOCK_DIM_Y * BLOCK_DIM_Z,
};
/// Shared memory storage layout type (last element from each thread's input)
struct _TempStorage
{
T first_items[BLOCK_THREADS];
T last_items[BLOCK_THREADS];
};
/******************************************************************************
* Utility methods
******************************************************************************/
/// Internal storage allocator
__device__ __forceinline__ _TempStorage& PrivateStorage()
{
__shared__ _TempStorage private_storage;
return private_storage;
}
/// Specialization for when FlagOp has third index param
template ::HAS_PARAM>
struct ApplyOp
{
// Apply flag operator
static __device__ __forceinline__ bool FlagT(FlagOp flag_op, const T &a, const T &b, int idx)
{
return flag_op(a, b, idx);
}
};
/// Specialization for when FlagOp does not have a third index param
template
struct ApplyOp
{
// Apply flag operator
static __device__ __forceinline__ bool FlagT(FlagOp flag_op, const T &a, const T &b, int /*idx*/)
{
return flag_op(a, b);
}
};
/// Templated unrolling of item comparison (inductive case)
template
struct Iterate
{
// Head flags
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
static __device__ __forceinline__ void FlagHeads(
int linear_tid,
FlagT (&flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
T (&preds)[ITEMS_PER_THREAD], ///< [out] Calling thread's predecessor items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
preds[ITERATION] = input[ITERATION - 1];
flags[ITERATION] = ApplyOp::FlagT(
flag_op,
preds[ITERATION],
input[ITERATION],
(linear_tid * ITEMS_PER_THREAD) + ITERATION);
Iterate::FlagHeads(linear_tid, flags, input, preds, flag_op);
}
// Tail flags
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
static __device__ __forceinline__ void FlagTails(
int linear_tid,
FlagT (&flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
flags[ITERATION] = ApplyOp::FlagT(
flag_op,
input[ITERATION],
input[ITERATION + 1],
(linear_tid * ITEMS_PER_THREAD) + ITERATION + 1);
Iterate::FlagTails(linear_tid, flags, input, flag_op);
}
};
/// Templated unrolling of item comparison (termination case)
template
struct Iterate
{
// Head flags
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
static __device__ __forceinline__ void FlagHeads(
int /*linear_tid*/,
FlagT (&/*flags*/)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&/*input*/)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
T (&/*preds*/)[ITEMS_PER_THREAD], ///< [out] Calling thread's predecessor items
FlagOp /*flag_op*/) ///< [in] Binary boolean flag predicate
{}
// Tail flags
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
static __device__ __forceinline__ void FlagTails(
int /*linear_tid*/,
FlagT (&/*flags*/)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&/*input*/)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp /*flag_op*/) ///< [in] Binary boolean flag predicate
{}
};
/******************************************************************************
* Thread fields
******************************************************************************/
/// Shared storage reference
_TempStorage &temp_storage;
/// Linear thread-id
unsigned int linear_tid;
public:
/// \smemstorage{BlockDiscontinuity}
struct TempStorage : Uninitialized<_TempStorage> {};
/******************************************************************//**
* \name Collective constructors
*********************************************************************/
//@{
/**
* \brief Collective constructor using a private static allocation of shared memory as temporary storage.
*/
__device__ __forceinline__ BlockDiscontinuity()
:
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__ BlockDiscontinuity(
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 Head flag operations
*********************************************************************/
//@{
#ifndef DOXYGEN_SHOULD_SKIP_THIS // Do not document
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeads(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
T (&preds)[ITEMS_PER_THREAD], ///< [out] Calling thread's predecessor items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
// Share last item
temp_storage.last_items[linear_tid] = input[ITEMS_PER_THREAD - 1];
CTA_SYNC();
if (linear_tid == 0)
{
// Set flag for first thread-item (preds[0] is undefined)
head_flags[0] = 1;
}
else
{
preds[0] = temp_storage.last_items[linear_tid - 1];
head_flags[0] = ApplyOp::FlagT(flag_op, preds[0], input[0], linear_tid * ITEMS_PER_THREAD);
}
// Set head_flags for remaining items
Iterate<1, ITEMS_PER_THREAD>::FlagHeads(linear_tid, head_flags, input, preds, flag_op);
}
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeads(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
T (&preds)[ITEMS_PER_THREAD], ///< [out] Calling thread's predecessor items
FlagOp flag_op, ///< [in] Binary boolean flag predicate
T tile_predecessor_item) ///< [in] [thread0 only] Item with which to compare the first tile item (input0 from thread0).
{
// Share last item
temp_storage.last_items[linear_tid] = input[ITEMS_PER_THREAD - 1];
CTA_SYNC();
// Set flag for first thread-item
preds[0] = (linear_tid == 0) ?
tile_predecessor_item : // First thread
temp_storage.last_items[linear_tid - 1];
head_flags[0] = ApplyOp::FlagT(flag_op, preds[0], input[0], linear_tid * ITEMS_PER_THREAD);
// Set head_flags for remaining items
Iterate<1, ITEMS_PER_THREAD>::FlagHeads(linear_tid, head_flags, input, preds, flag_op);
}
#endif // DOXYGEN_SHOULD_SKIP_THIS
/**
* \brief Sets head flags indicating discontinuities between items partitioned across the thread block, for which the first item has no reference and is always flagged.
*
* \par
* - The flag head_flagsi is set for item
* inputi when
* flag_op(previous-item, inputi)
* returns \p true (where previous-item is either the preceding item
* in the same thread or the last item in the previous thread).
* - For thread0, item input0 is always flagged.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the head-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Collectively compute head flags for discontinuities in the segment
* int head_flags[4];
* BlockDiscontinuity(temp_storage).FlagHeads(head_flags, thread_data, cub::Inequality());
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], [3,4,4,4], ... }.
* The corresponding output \p head_flags in those threads will be
* { [1,0,1,0], [0,0,0,0], [1,1,0,0], [0,1,0,0], ... }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeads(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
T preds[ITEMS_PER_THREAD];
FlagHeads(head_flags, input, preds, flag_op);
}
/**
* \brief Sets head flags indicating discontinuities between items partitioned across the thread block.
*
* \par
* - The flag head_flagsi is set for item
* inputi when
* flag_op(previous-item, inputi)
* returns \p true (where previous-item is either the preceding item
* in the same thread or the last item in the previous thread).
* - For thread0, item input0 is compared
* against \p tile_predecessor_item.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the head-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Have thread0 obtain the predecessor item for the entire tile
* int tile_predecessor_item;
* if (threadIdx.x == 0) tile_predecessor_item == ...
*
* // Collectively compute head flags for discontinuities in the segment
* int head_flags[4];
* BlockDiscontinuity(temp_storage).FlagHeads(
* head_flags, thread_data, cub::Inequality(), tile_predecessor_item);
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], [3,4,4,4], ... },
* and that \p tile_predecessor_item is \p 0. The corresponding output \p head_flags in those threads will be
* { [0,0,1,0], [0,0,0,0], [1,1,0,0], [0,1,0,0], ... }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeads(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op, ///< [in] Binary boolean flag predicate
T tile_predecessor_item) ///< [in] [thread0 only] Item with which to compare the first tile item (input0 from thread0).
{
T preds[ITEMS_PER_THREAD];
FlagHeads(head_flags, input, preds, flag_op, tile_predecessor_item);
}
//@} end member group
/******************************************************************//**
* \name Tail flag operations
*********************************************************************/
//@{
/**
* \brief Sets tail flags indicating discontinuities between items partitioned across the thread block, for which the last item has no reference and is always flagged.
*
* \par
* - The flag tail_flagsi is set for item
* inputi when
* flag_op(inputi, next-item)
* returns \p true (where next-item is either the next item
* in the same thread or the first item in the next thread).
* - For threadBLOCK_THREADS-1, item
* inputITEMS_PER_THREAD-1 is always flagged.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the tail-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Collectively compute tail flags for discontinuities in the segment
* int tail_flags[4];
* BlockDiscontinuity(temp_storage).FlagTails(tail_flags, thread_data, cub::Inequality());
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], ..., [124,125,125,125] }.
* The corresponding output \p tail_flags in those threads will be
* { [0,1,0,0], [0,0,0,1], [1,0,0,...], ..., [1,0,0,1] }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagTails(
FlagT (&tail_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity tail_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
// Share first item
temp_storage.first_items[linear_tid] = input[0];
CTA_SYNC();
// Set flag for last thread-item
tail_flags[ITEMS_PER_THREAD - 1] = (linear_tid == BLOCK_THREADS - 1) ?
1 : // Last thread
ApplyOp::FlagT(
flag_op,
input[ITEMS_PER_THREAD - 1],
temp_storage.first_items[linear_tid + 1],
(linear_tid * ITEMS_PER_THREAD) + ITEMS_PER_THREAD);
// Set tail_flags for remaining items
Iterate<0, ITEMS_PER_THREAD - 1>::FlagTails(linear_tid, tail_flags, input, flag_op);
}
/**
* \brief Sets tail flags indicating discontinuities between items partitioned across the thread block.
*
* \par
* - The flag tail_flagsi is set for item
* inputi when
* flag_op(inputi, next-item)
* returns \p true (where next-item is either the next item
* in the same thread or the first item in the next thread).
* - For threadBLOCK_THREADS-1, item
* inputITEMS_PER_THREAD-1 is compared
* against \p tile_successor_item.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the tail-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Have thread127 obtain the successor item for the entire tile
* int tile_successor_item;
* if (threadIdx.x == 127) tile_successor_item == ...
*
* // Collectively compute tail flags for discontinuities in the segment
* int tail_flags[4];
* BlockDiscontinuity(temp_storage).FlagTails(
* tail_flags, thread_data, cub::Inequality(), tile_successor_item);
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], ..., [124,125,125,125] }
* and that \p tile_successor_item is \p 125. The corresponding output \p tail_flags in those threads will be
* { [0,1,0,0], [0,0,0,1], [1,0,0,...], ..., [1,0,0,0] }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagTails(
FlagT (&tail_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity tail_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op, ///< [in] Binary boolean flag predicate
T tile_successor_item) ///< [in] [threadBLOCK_THREADS-1 only] Item with which to compare the last tile item (inputITEMS_PER_THREAD-1 from threadBLOCK_THREADS-1).
{
// Share first item
temp_storage.first_items[linear_tid] = input[0];
CTA_SYNC();
// Set flag for last thread-item
T successor_item = (linear_tid == BLOCK_THREADS - 1) ?
tile_successor_item : // Last thread
temp_storage.first_items[linear_tid + 1];
tail_flags[ITEMS_PER_THREAD - 1] = ApplyOp::FlagT(
flag_op,
input[ITEMS_PER_THREAD - 1],
successor_item,
(linear_tid * ITEMS_PER_THREAD) + ITEMS_PER_THREAD);
// Set tail_flags for remaining items
Iterate<0, ITEMS_PER_THREAD - 1>::FlagTails(linear_tid, tail_flags, input, flag_op);
}
//@} end member group
/******************************************************************//**
* \name Head & tail flag operations
*********************************************************************/
//@{
/**
* \brief Sets both head and tail flags indicating discontinuities between items partitioned across the thread block.
*
* \par
* - The flag head_flagsi is set for item
* inputi when
* flag_op(previous-item, inputi)
* returns \p true (where previous-item is either the preceding item
* in the same thread or the last item in the previous thread).
* - For thread0, item input0 is always flagged.
* - The flag tail_flagsi is set for item
* inputi when
* flag_op(inputi, next-item)
* returns \p true (where next-item is either the next item
* in the same thread or the first item in the next thread).
* - For threadBLOCK_THREADS-1, item
* inputITEMS_PER_THREAD-1 is always flagged.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the head- and tail-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Collectively compute head and flags for discontinuities in the segment
* int head_flags[4];
* int tail_flags[4];
* BlockDiscontinuity(temp_storage).FlagTails(
* head_flags, tail_flags, thread_data, cub::Inequality());
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], ..., [124,125,125,125] }
* and that the tile_successor_item is \p 125. The corresponding output \p head_flags
* in those threads will be { [1,0,1,0], [0,0,0,0], [1,1,0,0], [0,1,0,0], ... }.
* and the corresponding output \p tail_flags in those threads will be
* { [0,1,0,0], [0,0,0,1], [1,0,0,...], ..., [1,0,0,1] }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeadsAndTails(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
FlagT (&tail_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity tail_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
// Share first and last items
temp_storage.first_items[linear_tid] = input[0];
temp_storage.last_items[linear_tid] = input[ITEMS_PER_THREAD - 1];
CTA_SYNC();
T preds[ITEMS_PER_THREAD];
// Set flag for first thread-item
preds[0] = temp_storage.last_items[linear_tid - 1];
if (linear_tid == 0)
{
head_flags[0] = 1;
}
else
{
head_flags[0] = ApplyOp::FlagT(
flag_op,
preds[0],
input[0],
linear_tid * ITEMS_PER_THREAD);
}
// Set flag for last thread-item
tail_flags[ITEMS_PER_THREAD - 1] = (linear_tid == BLOCK_THREADS - 1) ?
1 : // Last thread
ApplyOp::FlagT(
flag_op,
input[ITEMS_PER_THREAD - 1],
temp_storage.first_items[linear_tid + 1],
(linear_tid * ITEMS_PER_THREAD) + ITEMS_PER_THREAD);
// Set head_flags for remaining items
Iterate<1, ITEMS_PER_THREAD>::FlagHeads(linear_tid, head_flags, input, preds, flag_op);
// Set tail_flags for remaining items
Iterate<0, ITEMS_PER_THREAD - 1>::FlagTails(linear_tid, tail_flags, input, flag_op);
}
/**
* \brief Sets both head and tail flags indicating discontinuities between items partitioned across the thread block.
*
* \par
* - The flag head_flagsi is set for item
* inputi when
* flag_op(previous-item, inputi)
* returns \p true (where previous-item is either the preceding item
* in the same thread or the last item in the previous thread).
* - For thread0, item input0 is always flagged.
* - The flag tail_flagsi is set for item
* inputi when
* flag_op(inputi, next-item)
* returns \p true (where next-item is either the next item
* in the same thread or the first item in the next thread).
* - For threadBLOCK_THREADS-1, item
* inputITEMS_PER_THREAD-1 is compared
* against \p tile_predecessor_item.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the head- and tail-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Have thread127 obtain the successor item for the entire tile
* int tile_successor_item;
* if (threadIdx.x == 127) tile_successor_item == ...
*
* // Collectively compute head and flags for discontinuities in the segment
* int head_flags[4];
* int tail_flags[4];
* BlockDiscontinuity(temp_storage).FlagTails(
* head_flags, tail_flags, tile_successor_item, thread_data, cub::Inequality());
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], ..., [124,125,125,125] }
* and that the tile_successor_item is \p 125. The corresponding output \p head_flags
* in those threads will be { [1,0,1,0], [0,0,0,0], [1,1,0,0], [0,1,0,0], ... }.
* and the corresponding output \p tail_flags in those threads will be
* { [0,1,0,0], [0,0,0,1], [1,0,0,...], ..., [1,0,0,0] }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeadsAndTails(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
FlagT (&tail_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity tail_flags
T tile_successor_item, ///< [in] [threadBLOCK_THREADS-1 only] Item with which to compare the last tile item (inputITEMS_PER_THREAD-1 from threadBLOCK_THREADS-1).
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
// Share first and last items
temp_storage.first_items[linear_tid] = input[0];
temp_storage.last_items[linear_tid] = input[ITEMS_PER_THREAD - 1];
CTA_SYNC();
T preds[ITEMS_PER_THREAD];
// Set flag for first thread-item
if (linear_tid == 0)
{
head_flags[0] = 1;
}
else
{
preds[0] = temp_storage.last_items[linear_tid - 1];
head_flags[0] = ApplyOp::FlagT(
flag_op,
preds[0],
input[0],
linear_tid * ITEMS_PER_THREAD);
}
// Set flag for last thread-item
T successor_item = (linear_tid == BLOCK_THREADS - 1) ?
tile_successor_item : // Last thread
temp_storage.first_items[linear_tid + 1];
tail_flags[ITEMS_PER_THREAD - 1] = ApplyOp::FlagT(
flag_op,
input[ITEMS_PER_THREAD - 1],
successor_item,
(linear_tid * ITEMS_PER_THREAD) + ITEMS_PER_THREAD);
// Set head_flags for remaining items
Iterate<1, ITEMS_PER_THREAD>::FlagHeads(linear_tid, head_flags, input, preds, flag_op);
// Set tail_flags for remaining items
Iterate<0, ITEMS_PER_THREAD - 1>::FlagTails(linear_tid, tail_flags, input, flag_op);
}
/**
* \brief Sets both head and tail flags indicating discontinuities between items partitioned across the thread block.
*
* \par
* - The flag head_flagsi is set for item
* inputi when
* flag_op(previous-item, inputi)
* returns \p true (where previous-item is either the preceding item
* in the same thread or the last item in the previous thread).
* - For thread0, item input0 is compared
* against \p tile_predecessor_item.
* - The flag tail_flagsi is set for item
* inputi when
* flag_op(inputi, next-item)
* returns \p true (where next-item is either the next item
* in the same thread or the first item in the next thread).
* - For threadBLOCK_THREADS-1, item
* inputITEMS_PER_THREAD-1 is always flagged.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the head- and tail-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Have thread0 obtain the predecessor item for the entire tile
* int tile_predecessor_item;
* if (threadIdx.x == 0) tile_predecessor_item == ...
*
* // Have thread127 obtain the successor item for the entire tile
* int tile_successor_item;
* if (threadIdx.x == 127) tile_successor_item == ...
*
* // Collectively compute head and flags for discontinuities in the segment
* int head_flags[4];
* int tail_flags[4];
* BlockDiscontinuity(temp_storage).FlagTails(
* head_flags, tile_predecessor_item, tail_flags, tile_successor_item,
* thread_data, cub::Inequality());
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], ..., [124,125,125,125] },
* that the \p tile_predecessor_item is \p 0, and that the
* \p tile_successor_item is \p 125. The corresponding output \p head_flags
* in those threads will be { [0,0,1,0], [0,0,0,0], [1,1,0,0], [0,1,0,0], ... }.
* and the corresponding output \p tail_flags in those threads will be
* { [0,1,0,0], [0,0,0,1], [1,0,0,...], ..., [1,0,0,1] }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeadsAndTails(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T tile_predecessor_item, ///< [in] [thread0 only] Item with which to compare the first tile item (input0 from thread0).
FlagT (&tail_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity tail_flags
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
// Share first and last items
temp_storage.first_items[linear_tid] = input[0];
temp_storage.last_items[linear_tid] = input[ITEMS_PER_THREAD - 1];
CTA_SYNC();
T preds[ITEMS_PER_THREAD];
// Set flag for first thread-item
preds[0] = (linear_tid == 0) ?
tile_predecessor_item : // First thread
temp_storage.last_items[linear_tid - 1];
head_flags[0] = ApplyOp::FlagT(
flag_op,
preds[0],
input[0],
linear_tid * ITEMS_PER_THREAD);
// Set flag for last thread-item
tail_flags[ITEMS_PER_THREAD - 1] = (linear_tid == BLOCK_THREADS - 1) ?
1 : // Last thread
ApplyOp::FlagT(
flag_op,
input[ITEMS_PER_THREAD - 1],
temp_storage.first_items[linear_tid + 1],
(linear_tid * ITEMS_PER_THREAD) + ITEMS_PER_THREAD);
// Set head_flags for remaining items
Iterate<1, ITEMS_PER_THREAD>::FlagHeads(linear_tid, head_flags, input, preds, flag_op);
// Set tail_flags for remaining items
Iterate<0, ITEMS_PER_THREAD - 1>::FlagTails(linear_tid, tail_flags, input, flag_op);
}
/**
* \brief Sets both head and tail flags indicating discontinuities between items partitioned across the thread block.
*
* \par
* - The flag head_flagsi is set for item
* inputi when
* flag_op(previous-item, inputi)
* returns \p true (where previous-item is either the preceding item
* in the same thread or the last item in the previous thread).
* - For thread0, item input0 is compared
* against \p tile_predecessor_item.
* - The flag tail_flagsi is set for item
* inputi when
* flag_op(inputi, next-item)
* returns \p true (where next-item is either the next item
* in the same thread or the first item in the next thread).
* - For threadBLOCK_THREADS-1, item
* inputITEMS_PER_THREAD-1 is compared
* against \p tile_successor_item.
* - \blocked
* - \granularity
* - \smemreuse
*
* \par Snippet
* The code snippet below illustrates the head- and tail-flagging of 512 integer items that
* are partitioned in a [blocked arrangement](index.html#sec5sec3) across 128 threads
* where each thread owns 4 consecutive items.
* \par
* \code
* #include // or equivalently
*
* __global__ void ExampleKernel(...)
* {
* // Specialize BlockDiscontinuity for a 1D block of 128 threads on type int
* typedef cub::BlockDiscontinuity BlockDiscontinuity;
*
* // Allocate shared memory for BlockDiscontinuity
* __shared__ typename BlockDiscontinuity::TempStorage temp_storage;
*
* // Obtain a segment of consecutive items that are blocked across threads
* int thread_data[4];
* ...
*
* // Have thread0 obtain the predecessor item for the entire tile
* int tile_predecessor_item;
* if (threadIdx.x == 0) tile_predecessor_item == ...
*
* // Have thread127 obtain the successor item for the entire tile
* int tile_successor_item;
* if (threadIdx.x == 127) tile_successor_item == ...
*
* // Collectively compute head and flags for discontinuities in the segment
* int head_flags[4];
* int tail_flags[4];
* BlockDiscontinuity(temp_storage).FlagTails(
* head_flags, tile_predecessor_item, tail_flags, tile_successor_item,
* thread_data, cub::Inequality());
*
* \endcode
* \par
* Suppose the set of input \p thread_data across the block of threads is
* { [0,0,1,1], [1,1,1,1], [2,3,3,3], ..., [124,125,125,125] },
* that the \p tile_predecessor_item is \p 0, and that the
* \p tile_successor_item is \p 125. The corresponding output \p head_flags
* in those threads will be { [0,0,1,0], [0,0,0,0], [1,1,0,0], [0,1,0,0], ... }.
* and the corresponding output \p tail_flags in those threads will be
* { [0,1,0,0], [0,0,0,1], [1,0,0,...], ..., [1,0,0,0] }.
*
* \tparam ITEMS_PER_THREAD [inferred] The number of consecutive items partitioned onto each thread.
* \tparam FlagT [inferred] The flag type (must be an integer type)
* \tparam FlagOp [inferred] Binary predicate functor type having member T operator()(const T &a, const T &b) or member T operator()(const T &a, const T &b, unsigned int b_index), and returning \p true if a discontinuity exists between \p a and \p b, otherwise \p false. \p b_index is the rank of b in the aggregate tile of data.
*/
template <
int ITEMS_PER_THREAD,
typename FlagT,
typename FlagOp>
__device__ __forceinline__ void FlagHeadsAndTails(
FlagT (&head_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity head_flags
T tile_predecessor_item, ///< [in] [thread0 only] Item with which to compare the first tile item (input0 from thread0).
FlagT (&tail_flags)[ITEMS_PER_THREAD], ///< [out] Calling thread's discontinuity tail_flags
T tile_successor_item, ///< [in] [threadBLOCK_THREADS-1 only] Item with which to compare the last tile item (inputITEMS_PER_THREAD-1 from threadBLOCK_THREADS-1).
T (&input)[ITEMS_PER_THREAD], ///< [in] Calling thread's input items
FlagOp flag_op) ///< [in] Binary boolean flag predicate
{
// Share first and last items
temp_storage.first_items[linear_tid] = input[0];
temp_storage.last_items[linear_tid] = input[ITEMS_PER_THREAD - 1];
CTA_SYNC();
T preds[ITEMS_PER_THREAD];
// Set flag for first thread-item
preds[0] = (linear_tid == 0) ?
tile_predecessor_item : // First thread
temp_storage.last_items[linear_tid - 1];
head_flags[0] = ApplyOp::FlagT(
flag_op,
preds[0],
input[0],
linear_tid * ITEMS_PER_THREAD);
// Set flag for last thread-item
T successor_item = (linear_tid == BLOCK_THREADS - 1) ?
tile_successor_item : // Last thread
temp_storage.first_items[linear_tid + 1];
tail_flags[ITEMS_PER_THREAD - 1] = ApplyOp::FlagT(
flag_op,
input[ITEMS_PER_THREAD - 1],
successor_item,
(linear_tid * ITEMS_PER_THREAD) + ITEMS_PER_THREAD);
// Set head_flags for remaining items
Iterate<1, ITEMS_PER_THREAD>::FlagHeads(linear_tid, head_flags, input, preds, flag_op);
// Set tail_flags for remaining items
Iterate<0, ITEMS_PER_THREAD - 1>::FlagTails(linear_tid, tail_flags, input, flag_op);
}
//@} end member group
};
} // CUB namespace
CUB_NS_POSTFIX // Optional outer namespace(s)