1 // -*- C++ -*- 2 3 // Copyright (C) 2007-2014 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/list_partition.h 26 * @brief _Functionality to split __sequence referenced by only input 27 * iterators. 28 * This file is a GNU parallel extension to the Standard C++ Library. 29 */ 30 31 // Written by Leonor Frias Moya and Johannes Singler. 32 33 #ifndef _GLIBCXX_PARALLEL_LIST_PARTITION_H 34 #define _GLIBCXX_PARALLEL_LIST_PARTITION_H 1 35 36 #include <parallel/parallel.h> 37 #include <vector> 38 39 namespace __gnu_parallel 40 { 41 /** @brief Shrinks and doubles the ranges. 42 * @param __os_starts Start positions worked on (oversampled). 43 * @param __count_to_two Counts up to 2. 44 * @param __range_length Current length of a chunk. 45 * @param __make_twice Whether the @c __os_starts is allowed to be 46 * grown or not 47 */ 48 template<typename _IIter> 49 void 50 __shrink_and_double(std::vector<_IIter>& __os_starts, 51 size_t& __count_to_two, size_t& __range_length, 52 const bool __make_twice) 53 { 54 ++__count_to_two; 55 if (!__make_twice || __count_to_two < 2) 56 __shrink(__os_starts, __count_to_two, __range_length); 57 else 58 { 59 __os_starts.resize((__os_starts.size() - 1) * 2 + 1); 60 __count_to_two = 0; 61 } 62 } 63 64 /** @brief Combines two ranges into one and thus halves the number of ranges. 65 * @param __os_starts Start positions worked on (oversampled). 66 * @param __count_to_two Counts up to 2. 67 * @param __range_length Current length of a chunk. */ 68 template<typename _IIter> 69 void 70 __shrink(std::vector<_IIter>& __os_starts, size_t& __count_to_two, 71 size_t& __range_length) 72 { 73 for (typename std::vector<_IIter>::size_type __i = 0; 74 __i <= (__os_starts.size() / 2); ++__i) 75 __os_starts[__i] = __os_starts[__i * 2]; 76 __range_length *= 2; 77 } 78 79 /** @brief Splits a sequence given by input iterators into parts of 80 * almost equal size 81 * 82 * The function needs only one pass over the sequence. 83 * @param __begin Begin iterator of input sequence. 84 * @param __end End iterator of input sequence. 85 * @param __starts Start iterators for the resulting parts, dimension 86 * @c __num_parts+1. For convenience, @c __starts @c [__num_parts] 87 * contains the end iterator of the sequence. 88 * @param __lengths Length of the resulting parts. 89 * @param __num_parts Number of parts to split the sequence into. 90 * @param __f Functor to be applied to each element by traversing __it 91 * @param __oversampling Oversampling factor. If 0, then the 92 * partitions will differ in at most 93 * \sqrt{\mathrm{__end} - \mathrm{__begin}} 94 * __elements. Otherwise, the ratio between the 95 * longest and the shortest part is bounded by 96 * 1/(\mathrm{__oversampling} \cdot \mathrm{num\_parts}) 97 * @return Length of the whole sequence. 98 */ 99 template<typename _IIter, typename _FunctorType> 100 size_t 101 list_partition(const _IIter __begin, const _IIter __end, 102 _IIter* __starts, size_t* __lengths, const int __num_parts, 103 _FunctorType& __f, int __oversampling = 0) 104 { 105 bool __make_twice = false; 106 107 // The resizing algorithm is chosen according to the oversampling factor. 108 if (__oversampling == 0) 109 { 110 __make_twice = true; 111 __oversampling = 1; 112 } 113 114 std::vector<_IIter> __os_starts(2 * __oversampling * __num_parts + 1); 115 116 __os_starts[0] = __begin; 117 _IIter __prev = __begin, __it = __begin; 118 size_t __dist_limit = 0, __dist = 0; 119 size_t __cur = 1, __next = 1; 120 size_t __range_length = 1; 121 size_t __count_to_two = 0; 122 while (__it != __end) 123 { 124 __cur = __next; 125 for (; __cur < __os_starts.size() and __it != __end; ++__cur) 126 { 127 for (__dist_limit += __range_length; 128 __dist < __dist_limit and __it != __end; ++__dist) 129 { 130 __f(__it); 131 ++__it; 132 } 133 __os_starts[__cur] = __it; 134 } 135 136 // Must compare for end and not __cur < __os_starts.size() , because 137 // __cur could be == __os_starts.size() as well 138 if (__it == __end) 139 break; 140 141 __shrink_and_double(__os_starts, __count_to_two, __range_length, 142 __make_twice); 143 __next = __os_starts.size() / 2 + 1; 144 } 145 146 // Calculation of the parts (one must be extracted from __current 147 // because the partition beginning at end, consists only of 148 // itself). 149 size_t __size_part = (__cur - 1) / __num_parts; 150 int __size_greater = static_cast<int>((__cur - 1) % __num_parts); 151 __starts[0] = __os_starts[0]; 152 153 size_t __index = 0; 154 155 // Smallest partitions. 156 for (int __i = 1; __i < (__num_parts + 1 - __size_greater); ++__i) 157 { 158 __lengths[__i - 1] = __size_part * __range_length; 159 __index += __size_part; 160 __starts[__i] = __os_starts[__index]; 161 } 162 163 // Biggest partitions. 164 for (int __i = __num_parts + 1 - __size_greater; __i <= __num_parts; 165 ++__i) 166 { 167 __lengths[__i - 1] = (__size_part+1) * __range_length; 168 __index += (__size_part+1); 169 __starts[__i] = __os_starts[__index]; 170 } 171 172 // Correction of the end size (the end iteration has not finished). 173 __lengths[__num_parts - 1] -= (__dist_limit - __dist); 174 175 return __dist; 176 } 177 } 178 179 #endif /* _GLIBCXX_PARALLEL_LIST_PARTITION_H */ 180
