Filename: //usr/include/c++///10/parallel//partial_sum.h

// -*- C++ -*- // Copyright (C) 2007-2020 Free Software Foundation, Inc. // // This file is part of the GNU ISO C++ Library. This library is free // software; you can redistribute it and/or modify it under the terms // of the GNU General Public License as published by the Free Software // Foundation; either version 3, or (at your option) any later // version. // This library is distributed in the hope that it will be useful, but // WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU // General Public License for more details. // Under Section 7 of GPL version 3, you are granted additional // permissions described in the GCC Runtime Library Exception, version // 3.1, as published by the Free Software Foundation. // You should have received a copy of the GNU General Public License and // a copy of the GCC Runtime Library Exception along with this program; // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see // <http://www.gnu.org/licenses/>. /** @file parallel/partial_sum.h * @brief Parallel implementation of std::partial_sum(), i.e. prefix * sums. * This file is a GNU parallel extension to the Standard C++ Library. */ // Written by Johannes Singler. #ifndef _GLIBCXX_PARALLEL_PARTIAL_SUM_H #define _GLIBCXX_PARALLEL_PARTIAL_SUM_H 1 #include <omp.h> #include <new> #include <bits/stl_algobase.h> #include <parallel/parallel.h> #include <parallel/numericfwd.h> namespace __gnu_parallel { // Problem: there is no 0-element given. /** @brief Base case prefix sum routine. * @param __begin Begin iterator of input sequence. * @param __end End iterator of input sequence. * @param __result Begin iterator of output sequence. * @param __bin_op Associative binary function. * @param __value Start value. Must be passed since the neutral * element is unknown in general. * @return End iterator of output sequence. */ template<typename _IIter, typename _OutputIterator, typename _BinaryOperation> _OutputIterator __parallel_partial_sum_basecase(_IIter __begin, _IIter __end, _OutputIterator __result, _BinaryOperation __bin_op, typename std::iterator_traits <_IIter>::value_type __value) { if (__begin == __end) return __result; while (__begin != __end) { __value = __bin_op(__value, *__begin); *__result = __value; ++__result; ++__begin; } return __result; } /** @brief Parallel partial sum implementation, two-phase approach, no recursion. * @param __begin Begin iterator of input sequence. * @param __end End iterator of input sequence. * @param __result Begin iterator of output sequence. * @param __bin_op Associative binary function. * @param __n Length of sequence. * @return End iterator of output sequence. */ template<typename _IIter, typename _OutputIterator, typename _BinaryOperation> _OutputIterator __parallel_partial_sum_linear(_IIter __begin, _IIter __end, _OutputIterator __result, _BinaryOperation __bin_op, typename std::iterator_traits<_IIter>::difference_type __n) { typedef std::iterator_traits<_IIter> _TraitsType; typedef typename _TraitsType::value_type _ValueType; typedef typename _TraitsType::difference_type _DifferenceType; if (__begin == __end) return __result; _ThreadIndex __num_threads = std::min<_DifferenceType>(__get_max_threads(), __n - 1); if (__num_threads < 2) { *__result = *__begin; return __parallel_partial_sum_basecase(__begin + 1, __end, __result + 1, __bin_op, *__begin); } _DifferenceType* __borders; _ValueType* __sums; const _Settings& __s = _Settings::get(); # pragma omp parallel num_threads(__num_threads) { # pragma omp single { __num_threads = omp_get_num_threads(); __borders = new _DifferenceType[__num_threads + 2]; if (__s.partial_sum_dilation == 1.0f) __equally_split(__n, __num_threads + 1, __borders); else { _DifferenceType __first_part_length = std::max<_DifferenceType>(1, __n / (1.0f + __s.partial_sum_dilation * __num_threads)); _DifferenceType __chunk_length = (__n - __first_part_length) / __num_threads; _DifferenceType __borderstart = __n - __num_threads * __chunk_length; __borders[0] = 0; for (_ThreadIndex __i = 1; __i < (__num_threads + 1); ++__i) { __borders[__i] = __borderstart; __borderstart += __chunk_length; } __borders[__num_threads + 1] = __n; } __sums = static_cast<_ValueType*>(::operator new(sizeof(_ValueType) * __num_threads)); _OutputIterator __target_end; } //single _ThreadIndex __iam = omp_get_thread_num(); if (__iam == 0) { *__result = *__begin; __parallel_partial_sum_basecase(__begin + 1, __begin + __borders[1], __result + 1, __bin_op, *__begin); ::new(&(__sums[__iam])) _ValueType(*(__result + __borders[1] - 1)); } else { ::new(&(__sums[__iam])) _ValueType(__gnu_parallel::accumulate( __begin + __borders[__iam] + 1, __begin + __borders[__iam + 1], *(__begin + __borders[__iam]), __bin_op, __gnu_parallel::sequential_tag())); } # pragma omp barrier # pragma omp single __parallel_partial_sum_basecase(__sums + 1, __sums + __num_threads, __sums + 1, __bin_op, __sums[0]); # pragma omp barrier // Still same team. __parallel_partial_sum_basecase(__begin + __borders[__iam + 1], __begin + __borders[__iam + 2], __result + __borders[__iam + 1], __bin_op, __sums[__iam]); } //parallel for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) __sums[__i].~_ValueType(); ::operator delete(__sums); delete[] __borders; return __result + __n; } /** @brief Parallel partial sum front-__end. * @param __begin Begin iterator of input sequence. * @param __end End iterator of input sequence. * @param __result Begin iterator of output sequence. * @param __bin_op Associative binary function. * @return End iterator of output sequence. */ template<typename _IIter, typename _OutputIterator, typename _BinaryOperation> _OutputIterator __parallel_partial_sum(_IIter __begin, _IIter __end, _OutputIterator __result, _BinaryOperation __bin_op) { _GLIBCXX_CALL(__begin - __end) typedef std::iterator_traits<_IIter> _TraitsType; typedef typename _TraitsType::value_type _ValueType; typedef typename _TraitsType::difference_type _DifferenceType; _DifferenceType __n = __end - __begin; switch (_Settings::get().partial_sum_algorithm) { case LINEAR: // Need an initial offset. return __parallel_partial_sum_linear(__begin, __end, __result, __bin_op, __n); default: // Partial_sum algorithm not implemented. _GLIBCXX_PARALLEL_ASSERT(0); return __result + __n; } } } #endif /* _GLIBCXX_PARALLEL_PARTIAL_SUM_H */

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