// -*- 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/quicksort.h * @brief Implementation of a unbalanced parallel quicksort (in-place). * This file is a GNU parallel extension to the Standard C++ Library. */ // Written by Johannes Singler. #ifndef _GLIBCXX_PARALLEL_QUICKSORT_H #define _GLIBCXX_PARALLEL_QUICKSORT_H 1 #include <parallel/parallel.h> #include <parallel/partition.h> namespace __gnu_parallel { /** @brief Unbalanced quicksort divide step. * @param __begin Begin iterator of subsequence. * @param __end End iterator of subsequence. * @param __comp Comparator. * @param __pivot_rank Desired __rank of the pivot. * @param __num_samples Choose pivot from that many samples. * @param __num_threads Number of threads that are allowed to work on * this part. */ template<typename _RAIter, typename _Compare> typename std::iterator_traits<_RAIter>::difference_type __parallel_sort_qs_divide(_RAIter __begin, _RAIter __end, _Compare __comp, typename std::iterator_traits <_RAIter>::difference_type __pivot_rank, typename std::iterator_traits <_RAIter>::difference_type __num_samples, _ThreadIndex __num_threads) { typedef std::iterator_traits<_RAIter> _TraitsType; typedef typename _TraitsType::value_type _ValueType; typedef typename _TraitsType::difference_type _DifferenceType; _DifferenceType __n = __end - __begin; __num_samples = std::min(__num_samples, __n); // Allocate uninitialized, to avoid default constructor. _ValueType* __samples = static_cast<_ValueType*> (::operator new(__num_samples * sizeof(_ValueType))); for (_DifferenceType __s = 0; __s < __num_samples; ++__s) { const unsigned long long __index = static_cast<unsigned long long> (__s) * __n / __num_samples; ::new(&(__samples[__s])) _ValueType(__begin[__index]); } __gnu_sequential::sort(__samples, __samples + __num_samples, __comp); _ValueType& __pivot = __samples[__pivot_rank * __num_samples / __n]; __gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool> __pred(__comp, __pivot); _DifferenceType __split = __parallel_partition(__begin, __end, __pred, __num_threads); for (_DifferenceType __s = 0; __s < __num_samples; ++__s) __samples[__s].~_ValueType(); ::operator delete(__samples); return __split; } /** @brief Unbalanced quicksort conquer step. * @param __begin Begin iterator of subsequence. * @param __end End iterator of subsequence. * @param __comp Comparator. * @param __num_threads Number of threads that are allowed to work on * this part. */ template<typename _RAIter, typename _Compare> void __parallel_sort_qs_conquer(_RAIter __begin, _RAIter __end, _Compare __comp, _ThreadIndex __num_threads) { typedef std::iterator_traits<_RAIter> _TraitsType; typedef typename _TraitsType::value_type _ValueType; typedef typename _TraitsType::difference_type _DifferenceType; if (__num_threads <= 1) { __gnu_sequential::sort(__begin, __end, __comp); return; } _DifferenceType __n = __end - __begin, __pivot_rank; if (__n <= 1) return; _ThreadIndex __num_threads_left; if ((__num_threads % 2) == 1) __num_threads_left = __num_threads / 2 + 1; else __num_threads_left = __num_threads / 2; __pivot_rank = __n * __num_threads_left / __num_threads; _DifferenceType __split = __parallel_sort_qs_divide (__begin, __end, __comp, __pivot_rank, _Settings::get().sort_qs_num_samples_preset, __num_threads); #pragma omp parallel sections num_threads(2) { #pragma omp section __parallel_sort_qs_conquer(__begin, __begin + __split, __comp, __num_threads_left); #pragma omp section __parallel_sort_qs_conquer(__begin + __split, __end, __comp, __num_threads - __num_threads_left); } } /** @brief Unbalanced quicksort main call. * @param __begin Begin iterator of input sequence. * @param __end End iterator input sequence, ignored. * @param __comp Comparator. * @param __num_threads Number of threads that are allowed to work on * this part. */ template<typename _RAIter, typename _Compare> void __parallel_sort_qs(_RAIter __begin, _RAIter __end, _Compare __comp, _ThreadIndex __num_threads) { _GLIBCXX_CALL(__n) typedef std::iterator_traits<_RAIter> _TraitsType; typedef typename _TraitsType::value_type _ValueType; typedef typename _TraitsType::difference_type _DifferenceType; _DifferenceType __n = __end - __begin; // At least one element per processor. if (__num_threads > __n) __num_threads = static_cast<_ThreadIndex>(__n); __parallel_sort_qs_conquer( __begin, __begin + __n, __comp, __num_threads); } } //namespace __gnu_parallel #endif /* _GLIBCXX_PARALLEL_QUICKSORT_H */