1// -*- C++ -*- 2 3// Copyright (C) 2007-2020 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/quicksort.h 26 * @brief Implementation of a unbalanced parallel quicksort (in-place). 27 * This file is a GNU parallel extension to the Standard C++ Library. 28 */ 29 30// Written by Johannes Singler. 31 32#ifndef _GLIBCXX_PARALLEL_QUICKSORT_H 33#define _GLIBCXX_PARALLEL_QUICKSORT_H 1 34 35#include <parallel/parallel.h> 36#include <parallel/partition.h> 37 38namespace __gnu_parallel 39{ 40 /** @brief Unbalanced quicksort divide step. 41 * @param __begin Begin iterator of subsequence. 42 * @param __end End iterator of subsequence. 43 * @param __comp Comparator. 44 * @param __pivot_rank Desired __rank of the pivot. 45 * @param __num_samples Choose pivot from that many samples. 46 * @param __num_threads Number of threads that are allowed to work on 47 * this part. 48 */ 49 template<typename _RAIter, typename _Compare> 50 typename std::iterator_traits<_RAIter>::difference_type 51 __parallel_sort_qs_divide(_RAIter __begin, _RAIter __end, 52 _Compare __comp, typename std::iterator_traits 53 <_RAIter>::difference_type __pivot_rank, 54 typename std::iterator_traits 55 <_RAIter>::difference_type 56 __num_samples, _ThreadIndex __num_threads) 57 { 58 typedef std::iterator_traits<_RAIter> _TraitsType; 59 typedef typename _TraitsType::value_type _ValueType; 60 typedef typename _TraitsType::difference_type _DifferenceType; 61 62 _DifferenceType __n = __end - __begin; 63 __num_samples = std::min(__num_samples, __n); 64 65 // Allocate uninitialized, to avoid default constructor. 66 _ValueType* __samples = static_cast<_ValueType*> 67 (::operator new(__num_samples * sizeof(_ValueType))); 68 69 for (_DifferenceType __s = 0; __s < __num_samples; ++__s) 70 { 71 const unsigned long long __index = static_cast<unsigned long long> 72 (__s) * __n / __num_samples; 73 ::new(&(__samples[__s])) _ValueType(__begin[__index]); 74 } 75 76 __gnu_sequential::sort(__samples, __samples + __num_samples, __comp); 77 78 _ValueType& __pivot = __samples[__pivot_rank * __num_samples / __n]; 79 80 __gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool> 81 __pred(__comp, __pivot); 82 _DifferenceType __split = __parallel_partition(__begin, __end, 83 __pred, __num_threads); 84 85 for (_DifferenceType __s = 0; __s < __num_samples; ++__s) 86 __samples[__s].~_ValueType(); 87 ::operator delete(__samples); 88 89 return __split; 90 } 91 92 /** @brief Unbalanced quicksort conquer step. 93 * @param __begin Begin iterator of subsequence. 94 * @param __end End iterator of subsequence. 95 * @param __comp Comparator. 96 * @param __num_threads Number of threads that are allowed to work on 97 * this part. 98 */ 99 template<typename _RAIter, typename _Compare> 100 void 101 __parallel_sort_qs_conquer(_RAIter __begin, _RAIter __end, 102 _Compare __comp, 103 _ThreadIndex __num_threads) 104 { 105 typedef std::iterator_traits<_RAIter> _TraitsType; 106 typedef typename _TraitsType::value_type _ValueType; 107 typedef typename _TraitsType::difference_type _DifferenceType; 108 109 if (__num_threads <= 1) 110 { 111 __gnu_sequential::sort(__begin, __end, __comp); 112 return; 113 } 114 115 _DifferenceType __n = __end - __begin, __pivot_rank; 116 117 if (__n <= 1) 118 return; 119 120 _ThreadIndex __num_threads_left; 121 122 if ((__num_threads % 2) == 1) 123 __num_threads_left = __num_threads / 2 + 1; 124 else 125 __num_threads_left = __num_threads / 2; 126 127 __pivot_rank = __n * __num_threads_left / __num_threads; 128 129 _DifferenceType __split = __parallel_sort_qs_divide 130 (__begin, __end, __comp, __pivot_rank, 131 _Settings::get().sort_qs_num_samples_preset, __num_threads); 132 133#pragma omp parallel sections num_threads(2) 134 { 135#pragma omp section 136 __parallel_sort_qs_conquer(__begin, __begin + __split, 137 __comp, __num_threads_left); 138#pragma omp section 139 __parallel_sort_qs_conquer(__begin + __split, __end, 140 __comp, __num_threads - __num_threads_left); 141 } 142 } 143 144 145 /** @brief Unbalanced quicksort main call. 146 * @param __begin Begin iterator of input sequence. 147 * @param __end End iterator input sequence, ignored. 148 * @param __comp Comparator. 149 * @param __num_threads Number of threads that are allowed to work on 150 * this part. 151 */ 152 template<typename _RAIter, typename _Compare> 153 void 154 __parallel_sort_qs(_RAIter __begin, _RAIter __end, 155 _Compare __comp, 156 _ThreadIndex __num_threads) 157 { 158 _GLIBCXX_CALL(__n) 159 160 typedef std::iterator_traits<_RAIter> _TraitsType; 161 typedef typename _TraitsType::value_type _ValueType; 162 typedef typename _TraitsType::difference_type _DifferenceType; 163 164 _DifferenceType __n = __end - __begin; 165 166 // At least one element per processor. 167 if (__num_threads > __n) 168 __num_threads = static_cast<_ThreadIndex>(__n); 169 170 __parallel_sort_qs_conquer( 171 __begin, __begin + __n, __comp, __num_threads); 172 } 173 174} //namespace __gnu_parallel 175 176#endif /* _GLIBCXX_PARALLEL_QUICKSORT_H */ 177