231 lines
7.3 KiB
C++
231 lines
7.3 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007-2022 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the terms
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// of the GNU General Public License as published by the Free Software
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// Foundation; either version 3, or (at your option) any later
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// version.
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// This library is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file parallel/partial_sum.h
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* @brief Parallel implementation of std::partial_sum(), i.e. prefix
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* sums.
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* This file is a GNU parallel extension to the Standard C++ Library.
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*/
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// Written by Johannes Singler.
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#ifndef _GLIBCXX_PARALLEL_PARTIAL_SUM_H
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#define _GLIBCXX_PARALLEL_PARTIAL_SUM_H 1
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#include <omp.h>
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#include <new>
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#include <bits/stl_algobase.h>
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#include <parallel/parallel.h>
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#include <parallel/numericfwd.h>
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namespace __gnu_parallel
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{
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// Problem: there is no 0-element given.
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/** @brief Base case prefix sum routine.
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* @param __begin Begin iterator of input sequence.
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* @param __end End iterator of input sequence.
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* @param __result Begin iterator of output sequence.
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* @param __bin_op Associative binary function.
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* @param __value Start value. Must be passed since the neutral
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* element is unknown in general.
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* @return End iterator of output sequence. */
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template<typename _IIter,
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typename _OutputIterator,
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typename _BinaryOperation>
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_OutputIterator
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__parallel_partial_sum_basecase(_IIter __begin, _IIter __end,
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_OutputIterator __result,
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_BinaryOperation __bin_op,
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typename std::iterator_traits <_IIter>::value_type __value)
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{
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if (__begin == __end)
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return __result;
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while (__begin != __end)
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{
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__value = __bin_op(__value, *__begin);
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*__result = __value;
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++__result;
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++__begin;
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}
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return __result;
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}
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/** @brief Parallel partial sum implementation, two-phase approach,
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no recursion.
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* @param __begin Begin iterator of input sequence.
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* @param __end End iterator of input sequence.
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* @param __result Begin iterator of output sequence.
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* @param __bin_op Associative binary function.
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* @param __n Length of sequence.
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* @return End iterator of output sequence.
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*/
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template<typename _IIter,
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typename _OutputIterator,
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typename _BinaryOperation>
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_OutputIterator
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__parallel_partial_sum_linear(_IIter __begin, _IIter __end,
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_OutputIterator __result,
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_BinaryOperation __bin_op,
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typename std::iterator_traits<_IIter>::difference_type __n)
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{
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typedef std::iterator_traits<_IIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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if (__begin == __end)
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return __result;
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_ThreadIndex __num_threads =
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std::min<_DifferenceType>(__get_max_threads(), __n - 1);
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if (__num_threads < 2)
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{
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*__result = *__begin;
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return __parallel_partial_sum_basecase(__begin + 1, __end,
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__result + 1, __bin_op,
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*__begin);
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}
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_DifferenceType* __borders;
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_ValueType* __sums;
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const _Settings& __s = _Settings::get();
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# pragma omp parallel num_threads(__num_threads)
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{
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# pragma omp single
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{
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__num_threads = omp_get_num_threads();
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__borders = new _DifferenceType[__num_threads + 2];
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if (__s.partial_sum_dilation == 1.0f)
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__equally_split(__n, __num_threads + 1, __borders);
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else
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{
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_DifferenceType __first_part_length =
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std::max<_DifferenceType>(1,
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__n / (1.0f + __s.partial_sum_dilation * __num_threads));
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_DifferenceType __chunk_length =
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(__n - __first_part_length) / __num_threads;
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_DifferenceType __borderstart =
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__n - __num_threads * __chunk_length;
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__borders[0] = 0;
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for (_ThreadIndex __i = 1; __i < (__num_threads + 1); ++__i)
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{
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__borders[__i] = __borderstart;
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__borderstart += __chunk_length;
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}
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__borders[__num_threads + 1] = __n;
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}
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__sums = static_cast<_ValueType*>(::operator new(sizeof(_ValueType)
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* __num_threads));
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_OutputIterator __target_end;
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} //single
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_ThreadIndex __iam = omp_get_thread_num();
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if (__iam == 0)
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{
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*__result = *__begin;
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__parallel_partial_sum_basecase(__begin + 1,
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__begin + __borders[1],
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__result + 1,
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__bin_op, *__begin);
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::new(&(__sums[__iam])) _ValueType(*(__result + __borders[1] - 1));
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}
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else
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{
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::new(&(__sums[__iam]))
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_ValueType(__gnu_parallel::accumulate(
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__begin + __borders[__iam] + 1,
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__begin + __borders[__iam + 1],
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*(__begin + __borders[__iam]),
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__bin_op,
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__gnu_parallel::sequential_tag()));
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}
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# pragma omp barrier
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# pragma omp single
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__parallel_partial_sum_basecase(__sums + 1, __sums + __num_threads,
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__sums + 1, __bin_op, __sums[0]);
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# pragma omp barrier
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// Still same team.
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__parallel_partial_sum_basecase(__begin + __borders[__iam + 1],
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__begin + __borders[__iam + 2],
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__result + __borders[__iam + 1],
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__bin_op, __sums[__iam]);
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} //parallel
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for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
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__sums[__i].~_ValueType();
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::operator delete(__sums);
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delete[] __borders;
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return __result + __n;
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}
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/** @brief Parallel partial sum front-__end.
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* @param __begin Begin iterator of input sequence.
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* @param __end End iterator of input sequence.
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* @param __result Begin iterator of output sequence.
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* @param __bin_op Associative binary function.
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* @return End iterator of output sequence. */
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template<typename _IIter,
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typename _OutputIterator,
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typename _BinaryOperation>
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_OutputIterator
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__parallel_partial_sum(_IIter __begin, _IIter __end,
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_OutputIterator __result, _BinaryOperation __bin_op)
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{
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_GLIBCXX_CALL(__begin - __end)
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typedef std::iterator_traits<_IIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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_DifferenceType __n = __end - __begin;
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switch (_Settings::get().partial_sum_algorithm)
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{
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case LINEAR:
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// Need an initial offset.
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return __parallel_partial_sum_linear(__begin, __end, __result,
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__bin_op, __n);
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default:
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// Partial_sum algorithm not implemented.
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_GLIBCXX_PARALLEL_ASSERT(0);
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return __result + __n;
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}
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}
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}
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#endif /* _GLIBCXX_PARALLEL_PARTIAL_SUM_H */
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