OpenVDB: nanovdb/util/PrefixSum.h Source File

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PrefixSum.h
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1// Copyright Contributors to the OpenVDB Project
2// SPDX-License-Identifier: Apache-2.0
3
4/*!
5 \file nanovdb/util/PrefixSum.h
6
7 \author Ken Museth
8
9 \date March 12, 2023
10
11 \brief Multi-threaded implementations of inclusive prefix sum
12
13 \note An exclusive prefix sum is simply an array starting with zero
14 followed by the elements in the inclusive prefix sum, minus its
15 last entry which is the sum of all the input elements.
16*/
17
18#ifndef NANOVDB_UTIL_PREFIX_SUM_H_HAS_BEEN_INCLUDED
19#define NANOVDB_UTIL_PREFIX_SUM_H_HAS_BEEN_INCLUDED
20
21#include <nanovdb/util/Range.h>// for Range1D
22#include <vector>
23#include <functional>// for std::plus
24
25#ifdef NANOVDB_USE_TBB
26#include <tbb/parallel_scan.h>
27#endif
28
29namespace nanovdb {
30
31namespace util {
32
33/// @brief Computes inclusive prefix sum of a vector
34/// @tparam T Type of the elements in the input/out vector
35/// @tparam OpT Type of operation performed on each element (defaults to sum)
36/// @param vec input and output vector
37/// @param threaded if true multi-threading is used
38/// @note Inclusive prefix sum: for (i=1; i<N; ++i) vec[i] += vec[i-1]
39/// @return sum of all input elements, which is also the last element of the inclusive prefix sum
40template<typename T, typename OpT = std::plus<T>>
41T prefixSum(std::vector<T> &vec, bool threaded = true, OpT op = OpT());
42
43/// @brief An inclusive scan includes in[i] when computing out[i]
44/// @note Inclusive prefix operation: for (i=1; i<N; ++i) vec[i] = Op(vec[i],vec[i-1])
45template<typename T, typename Op>
46 void inclusiveScan(T *array, size_t size, const T &identity, bool threaded, Op op)
47{
48#ifndef NANOVDB_USE_TBB
49 threaded = false;
50 (void)identity;// avoids compiler warning
51#endif
52
53 if (threaded) {
54#ifdef NANOVDB_USE_TBB
55 using RangeT = tbb::blocked_range<size_t>;
56 tbb::parallel_scan(RangeT(0, size), identity,
57 [&](const RangeT &r, T sum, bool is_final_scan)->T {
58 T tmp = sum;
59 for (size_t i = r.begin(); i < r.end(); ++i) {
60 tmp = op(tmp, array[i]);
61 if (is_final_scan) array[i] = tmp;
62 }
63 return tmp;
64 },[&](const T &a, const T &b) {return op(a, b);}
65 );
66#endif
67 } else { // serial inclusive prefix operation
68 for (size_t i=1; i<size; ++i) array[i] = op(array[i], array[i-1]);
69 }
70}// inclusiveScan
71
72template<typename T, typename OpT>
73T prefixSum(std::vector<T> &vec, bool threaded, OpT op)
74{
75 inclusiveScan(vec.data(), vec.size(), T(0), threaded, op);
76 return vec.back();// sum of all input elements
77}// prefixSum
78
79}// namespace util
80
81template<typename T, typename OpT = std::plus<T>>
82[[deprecated("Use nanovdb::util::prefixSum instead")]]
83T prefixSum(std::vector<T> &vec, bool threaded = true, OpT op = OpT())
84{
85 return util::prefixSum<T, OpT>(vec, threaded, op);
86}// prefixSum
87
88}// namespace nanovdb
89
90#endif // NANOVDB_UTIL_PREFIX_SUM_H_HAS_BEEN_INCLUDED
Range.h
Custom Range class that is compatible with the tbb::blocked_range classes.
nanovdb::util
Definition ForEach.h:29
nanovdb::util::prefixSum
T prefixSum(std::vector< T > &vec, bool threaded=true, OpT op=OpT())
Computes inclusive prefix sum of a vector.
Definition PrefixSum.h:73
nanovdb::util::inclusiveScan
void inclusiveScan(T *array, size_t size, const T &identity, bool threaded, Op op)
An inclusive scan includes in[i] when computing out[i].
Definition PrefixSum.h:46
nanovdb
Definition GridHandle.h:27
nanovdb::prefixSum
T prefixSum(std::vector< T > &vec, bool threaded=true, OpT op=OpT())
Definition PrefixSum.h:83