libstdc++
quicksort.h
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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 
38 namespace __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>
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 #pragma GCC diagnostic push
70 #pragma GCC diagnostic ignored "-Wlong-long" // LL literal
71  for (_DifferenceType __s = 0; __s < __num_samples; ++__s)
72  {
73  const unsigned long long __index = static_cast<unsigned long long>
74  (__s) * __n / __num_samples;
75  ::new(&(__samples[__s])) _ValueType(__begin[__index]);
76  }
77 #pragma GCC diagnostic pop
78 
79  __gnu_sequential::sort(__samples, __samples + __num_samples, __comp);
80 
81  _ValueType& __pivot = __samples[__pivot_rank * __num_samples / __n];
82 
84  __pred(__comp, __pivot);
85  _DifferenceType __split = __parallel_partition(__begin, __end,
86  __pred, __num_threads);
87 
88  for (_DifferenceType __s = 0; __s < __num_samples; ++__s)
89  __samples[__s].~_ValueType();
90  ::operator delete(__samples);
91 
92  return __split;
93  }
94 
95  /** @brief Unbalanced quicksort conquer step.
96  * @param __begin Begin iterator of subsequence.
97  * @param __end End iterator of subsequence.
98  * @param __comp Comparator.
99  * @param __num_threads Number of threads that are allowed to work on
100  * this part.
101  */
102  template<typename _RAIter, typename _Compare>
103  void
104  __parallel_sort_qs_conquer(_RAIter __begin, _RAIter __end,
105  _Compare __comp,
106  _ThreadIndex __num_threads)
107  {
108  typedef std::iterator_traits<_RAIter> _TraitsType;
109  typedef typename _TraitsType::value_type _ValueType;
110  typedef typename _TraitsType::difference_type _DifferenceType;
111 
112  if (__num_threads <= 1)
113  {
114  __gnu_sequential::sort(__begin, __end, __comp);
115  return;
116  }
117 
118  _DifferenceType __n = __end - __begin, __pivot_rank;
119 
120  if (__n <= 1)
121  return;
122 
123  _ThreadIndex __num_threads_left;
124 
125  if ((__num_threads % 2) == 1)
126  __num_threads_left = __num_threads / 2 + 1;
127  else
128  __num_threads_left = __num_threads / 2;
129 
130  __pivot_rank = __n * __num_threads_left / __num_threads;
131 
132  _DifferenceType __split = __parallel_sort_qs_divide
133  (__begin, __end, __comp, __pivot_rank,
134  _Settings::get().sort_qs_num_samples_preset, __num_threads);
135 
136 #pragma omp parallel sections num_threads(2)
137  {
138 #pragma omp section
139  __parallel_sort_qs_conquer(__begin, __begin + __split,
140  __comp, __num_threads_left);
141 #pragma omp section
142  __parallel_sort_qs_conquer(__begin + __split, __end,
143  __comp, __num_threads - __num_threads_left);
144  }
145  }
146 
147 
148  /** @brief Unbalanced quicksort main call.
149  * @param __begin Begin iterator of input sequence.
150  * @param __end End iterator input sequence, ignored.
151  * @param __comp Comparator.
152  * @param __num_threads Number of threads that are allowed to work on
153  * this part.
154  */
155  template<typename _RAIter, typename _Compare>
156  void
157  __parallel_sort_qs(_RAIter __begin, _RAIter __end,
158  _Compare __comp,
159  _ThreadIndex __num_threads)
160  {
161  _GLIBCXX_CALL(__n)
162 
163  typedef std::iterator_traits<_RAIter> _TraitsType;
164  typedef typename _TraitsType::value_type _ValueType;
165  typedef typename _TraitsType::difference_type _DifferenceType;
166 
167  _DifferenceType __n = __end - __begin;
168 
169  // At least one element per processor.
170  if (__num_threads > __n)
171  __num_threads = static_cast<_ThreadIndex>(__n);
172 
174  __begin, __begin + __n, __comp, __num_threads);
175  }
176 
177 } //namespace __gnu_parallel
178 
179 #endif /* _GLIBCXX_PARALLEL_QUICKSORT_H */
#define _GLIBCXX_CALL(__n)
Macro to produce log message when entering a function.
End-user include file. Provides advanced settings and tuning options. This file is a GNU parallel ext...
Parallel implementation of std::partition(), std::nth_element(), and std::partial_sort()....
constexpr const _Tp & min(const _Tp &, const _Tp &)
This does what you think it does.
Definition: stl_algobase.h:234
GNU parallel code for public use.
uint16_t _ThreadIndex
Unsigned integer to index a thread number. The maximum thread number (for each processor) must fit in...
Definition: types.h:123
void __parallel_sort_qs_conquer(_RAIter __begin, _RAIter __end, _Compare __comp, _ThreadIndex __num_threads)
Unbalanced quicksort conquer step.
Definition: quicksort.h:104
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)
Unbalanced quicksort divide step.
Definition: quicksort.h:51
std::iterator_traits< _RAIter >::difference_type __parallel_partition(_RAIter __begin, _RAIter __end, _Predicate __pred, _ThreadIndex __num_threads)
Parallel implementation of std::partition.
Definition: partition.h:56
void __parallel_sort_qs(_RAIter __begin, _RAIter __end, _Compare __comp, _ThreadIndex __num_threads)
Unbalanced quicksort main call.
Definition: quicksort.h:157
Traits class for iterators.
Similar to std::binder2nd, but giving the argument types explicitly.
Definition: base.h:224
static const _Settings & get()
Get the global settings.