1 // -*- C++ -*- 2 3 // Copyright (C) 2007-2022 Free Software Foundation, Inc. 4 // 5 // This file is part of the GNU ISO C++ Library. This library is free 6 // software; you can redistribute it and/or modify it under the terms 7 // of the GNU General Public License as published by the Free Software 8 // Foundation; either version 3, or (at your option) any later 9 // version. 10 11 // This library is distributed in the hope that it will be useful, but 12 // WITHOUT ANY WARRANTY; without even the implied warranty of 13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 // General Public License for more details. 15 16 // Under Section 7 of GPL version 3, you are granted additional 17 // permissions described in the GCC Runtime Library Exception, version 18 // 3.1, as published by the Free Software Foundation. 19 20 // You should have received a copy of the GNU General Public License and 21 // a copy of the GCC Runtime Library Exception along with this program; 22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 // <http://www.gnu.org/licenses/>. 24 25 /** @file parallel/partial_sum.h 26 * @brief Parallel implementation of std::partial_sum(), i.e. prefix 27 * sums. 28 * This file is a GNU parallel extension to the Standard C++ Library. 29 */ 30 31 // Written by Johannes Singler. 32 33 #ifndef _GLIBCXX_PARALLEL_PARTIAL_SUM_H 34 #define _GLIBCXX_PARALLEL_PARTIAL_SUM_H 1 35 36 #include <omp.h> 37 #include <new> 38 #include <bits/stl_algobase.h> 39 #include <parallel/parallel.h> 40 #include <parallel/numericfwd.h> 41 42 namespace __gnu_parallel 43 { 44 // Problem: there is no 0-element given. 45 46 /** @brief Base case prefix sum routine. 47 * @param __begin Begin iterator of input sequence. 48 * @param __end End iterator of input sequence. 49 * @param __result Begin iterator of output sequence. 50 * @param __bin_op Associative binary function. 51 * @param __value Start value. Must be passed since the neutral 52 * element is unknown in general. 53 * @return End iterator of output sequence. */ 54 template<typename _IIter, 55 typename _OutputIterator, 56 typename _BinaryOperation> 57 _OutputIterator __parallel_partial_sum_basecase(_IIter __begin,_IIter __end,_OutputIterator __result,_BinaryOperation __bin_op,typename std::iterator_traits<_IIter>::value_type __value)58 __parallel_partial_sum_basecase(_IIter __begin, _IIter __end, 59 _OutputIterator __result, 60 _BinaryOperation __bin_op, 61 typename std::iterator_traits <_IIter>::value_type __value) 62 { 63 if (__begin == __end) 64 return __result; 65 66 while (__begin != __end) 67 { 68 __value = __bin_op(__value, *__begin); 69 *__result = __value; 70 ++__result; 71 ++__begin; 72 } 73 return __result; 74 } 75 76 /** @brief Parallel partial sum implementation, two-phase approach, 77 no recursion. 78 * @param __begin Begin iterator of input sequence. 79 * @param __end End iterator of input sequence. 80 * @param __result Begin iterator of output sequence. 81 * @param __bin_op Associative binary function. 82 * @param __n Length of sequence. 83 * @return End iterator of output sequence. 84 */ 85 template<typename _IIter, 86 typename _OutputIterator, 87 typename _BinaryOperation> 88 _OutputIterator __parallel_partial_sum_linear(_IIter __begin,_IIter __end,_OutputIterator __result,_BinaryOperation __bin_op,typename std::iterator_traits<_IIter>::difference_type __n)89 __parallel_partial_sum_linear(_IIter __begin, _IIter __end, 90 _OutputIterator __result, 91 _BinaryOperation __bin_op, 92 typename std::iterator_traits<_IIter>::difference_type __n) 93 { 94 typedef std::iterator_traits<_IIter> _TraitsType; 95 typedef typename _TraitsType::value_type _ValueType; 96 typedef typename _TraitsType::difference_type _DifferenceType; 97 98 if (__begin == __end) 99 return __result; 100 101 _ThreadIndex __num_threads = 102 std::min<_DifferenceType>(__get_max_threads(), __n - 1); 103 104 if (__num_threads < 2) 105 { 106 *__result = *__begin; 107 return __parallel_partial_sum_basecase(__begin + 1, __end, 108 __result + 1, __bin_op, 109 *__begin); 110 } 111 112 _DifferenceType* __borders; 113 _ValueType* __sums; 114 115 const _Settings& __s = _Settings::get(); 116 117 # pragma omp parallel num_threads(__num_threads) 118 { 119 # pragma omp single 120 { 121 __num_threads = omp_get_num_threads(); 122 123 __borders = new _DifferenceType[__num_threads + 2]; 124 125 if (__s.partial_sum_dilation == 1.0f) 126 __equally_split(__n, __num_threads + 1, __borders); 127 else 128 { 129 _DifferenceType __first_part_length = 130 std::max<_DifferenceType>(1, 131 __n / (1.0f + __s.partial_sum_dilation * __num_threads)); 132 _DifferenceType __chunk_length = 133 (__n - __first_part_length) / __num_threads; 134 _DifferenceType __borderstart = 135 __n - __num_threads * __chunk_length; 136 __borders[0] = 0; 137 for (_ThreadIndex __i = 1; __i < (__num_threads + 1); ++__i) 138 { 139 __borders[__i] = __borderstart; 140 __borderstart += __chunk_length; 141 } 142 __borders[__num_threads + 1] = __n; 143 } 144 145 __sums = static_cast<_ValueType*>(::operator new(sizeof(_ValueType) 146 * __num_threads)); 147 _OutputIterator __target_end; 148 } //single 149 150 _ThreadIndex __iam = omp_get_thread_num(); 151 if (__iam == 0) 152 { 153 *__result = *__begin; 154 __parallel_partial_sum_basecase(__begin + 1, 155 __begin + __borders[1], 156 __result + 1, 157 __bin_op, *__begin); 158 ::new(&(__sums[__iam])) _ValueType(*(__result + __borders[1] - 1)); 159 } 160 else 161 { 162 ::new(&(__sums[__iam])) 163 _ValueType(__gnu_parallel::accumulate( 164 __begin + __borders[__iam] + 1, 165 __begin + __borders[__iam + 1], 166 *(__begin + __borders[__iam]), 167 __bin_op, 168 __gnu_parallel::sequential_tag())); 169 } 170 171 # pragma omp barrier 172 173 # pragma omp single 174 __parallel_partial_sum_basecase(__sums + 1, __sums + __num_threads, 175 __sums + 1, __bin_op, __sums[0]); 176 177 # pragma omp barrier 178 179 // Still same team. 180 __parallel_partial_sum_basecase(__begin + __borders[__iam + 1], 181 __begin + __borders[__iam + 2], 182 __result + __borders[__iam + 1], 183 __bin_op, __sums[__iam]); 184 } //parallel 185 186 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) 187 __sums[__i].~_ValueType(); 188 ::operator delete(__sums); 189 190 delete[] __borders; 191 192 return __result + __n; 193 } 194 195 /** @brief Parallel partial sum front-__end. 196 * @param __begin Begin iterator of input sequence. 197 * @param __end End iterator of input sequence. 198 * @param __result Begin iterator of output sequence. 199 * @param __bin_op Associative binary function. 200 * @return End iterator of output sequence. */ 201 template<typename _IIter, 202 typename _OutputIterator, 203 typename _BinaryOperation> 204 _OutputIterator __parallel_partial_sum(_IIter __begin,_IIter __end,_OutputIterator __result,_BinaryOperation __bin_op)205 __parallel_partial_sum(_IIter __begin, _IIter __end, 206 _OutputIterator __result, _BinaryOperation __bin_op) 207 { 208 _GLIBCXX_CALL(__begin - __end) 209 210 typedef std::iterator_traits<_IIter> _TraitsType; 211 typedef typename _TraitsType::value_type _ValueType; 212 typedef typename _TraitsType::difference_type _DifferenceType; 213 214 _DifferenceType __n = __end - __begin; 215 216 switch (_Settings::get().partial_sum_algorithm) 217 { 218 case LINEAR: 219 // Need an initial offset. 220 return __parallel_partial_sum_linear(__begin, __end, __result, 221 __bin_op, __n); 222 default: 223 // Partial_sum algorithm not implemented. 224 _GLIBCXX_PARALLEL_ASSERT(0); 225 return __result + __n; 226 } 227 } 228 } 229 230 #endif /* _GLIBCXX_PARALLEL_PARTIAL_SUM_H */ 231