quicksort.h
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// -*- C++ -*-
// Copyright (C) 2007-2013 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 */