// -*- C++ -*-
// Copyright (C) 2007, 2008, 2009 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/multiway_merge.h
* @brief Implementation of sequential and parallel multiway merge.
*
* Explanations on the high-speed merging routines in the appendix of
*
* P. Sanders.
* Fast priority queues for cached memory.
* ACM Journal of Experimental Algorithmics, 5, 2000.
*
* This file is a GNU parallel extension to the Standard C++ Library.
*/
// Written by Johannes Singler and Manuel Holtgrewe.
#ifndef _GLIBCXX_PARALLEL_MULTIWAY_MERGE_H
#define _GLIBCXX_PARALLEL_MULTIWAY_MERGE_H
#include <vector>
#include <bits/stl_algo.h>
#include <parallel/features.h>
#include <parallel/parallel.h>
#include <parallel/losertree.h>
#if _GLIBCXX_ASSERTIONS
#include <parallel/checkers.h>
#endif
/** @brief Length of a sequence described by a pair of iterators. */
#define _GLIBCXX_PARALLEL_LENGTH(s) ((s).second - (s).first)
namespace __gnu_parallel
{
// Announce guarded and unguarded iterator.
template<typename RandomAccessIterator, typename Comparator>
class guarded_iterator;
// Making the arguments const references seems to dangerous,
// the user-defined comparator might not be const.
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<(guarded_iterator<RandomAccessIterator, Comparator>& bi1,
guarded_iterator<RandomAccessIterator, Comparator>& bi2);
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<=(guarded_iterator<RandomAccessIterator, Comparator>& bi1,
guarded_iterator<RandomAccessIterator, Comparator>& bi2);
/** @brief Iterator wrapper supporting an implicit supremum at the end
* of the sequence, dominating all comparisons.
*
* The implicit supremum comes with a performance cost.
*
* Deriving from RandomAccessIterator is not possible since
* RandomAccessIterator need not be a class.
*/
template<typename RandomAccessIterator, typename Comparator>
class guarded_iterator
{
private:
/** @brief Current iterator position. */
RandomAccessIterator current;
/** @brief End iterator of the sequence. */
RandomAccessIterator end;
/** @brief Comparator. */
Comparator& comp;
public:
/** @brief Constructor. Sets iterator to beginning of sequence.
* @param begin Begin iterator of sequence.
* @param end End iterator of sequence.
* @param comp Comparator provided for associated overloaded
* compare operators. */
guarded_iterator(RandomAccessIterator begin,
RandomAccessIterator end, Comparator& comp)
: current(begin), end(end), comp(comp)
{ }
/** @brief Pre-increment operator.
* @return This. */
guarded_iterator<RandomAccessIterator, Comparator>&
operator++()
{
++current;
return *this;
}
/** @brief Dereference operator.
* @return Referenced element. */
typename std::iterator_traits<RandomAccessIterator>::value_type&
operator*()
{ return *current; }
/** @brief Convert to wrapped iterator.
* @return Wrapped iterator. */
operator RandomAccessIterator()
{ return current; }
friend bool
operator< <RandomAccessIterator, Comparator>(
guarded_iterator<RandomAccessIterator, Comparator>& bi1,
guarded_iterator<RandomAccessIterator, Comparator>& bi2);
friend bool
operator<= <RandomAccessIterator, Comparator>(
guarded_iterator<RandomAccessIterator, Comparator>& bi1,
guarded_iterator<RandomAccessIterator, Comparator>& bi2);
};
/** @brief Compare two elements referenced by guarded iterators.
* @param bi1 First iterator.
* @param bi2 Second iterator.
* @return @c True if less. */
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<(guarded_iterator<RandomAccessIterator, Comparator>& bi1,
guarded_iterator<RandomAccessIterator, Comparator>& bi2)
{
if (bi1.current == bi1.end) //bi1 is sup
return bi2.current == bi2.end; //bi2 is not sup
if (bi2.current == bi2.end) //bi2 is sup
return true;
return (bi1.comp)(*bi1, *bi2); //normal compare
}
/** @brief Compare two elements referenced by guarded iterators.
* @param bi1 First iterator.
* @param bi2 Second iterator.
* @return @c True if less equal. */
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<=(guarded_iterator<RandomAccessIterator, Comparator>& bi1,
guarded_iterator<RandomAccessIterator, Comparator>& bi2)
{
if (bi2.current == bi2.end) //bi1 is sup
return bi1.current != bi1.end; //bi2 is not sup
if (bi1.current == bi1.end) //bi2 is sup
return false;
return !(bi1.comp)(*bi2, *bi1); //normal compare
}
template<typename RandomAccessIterator, typename Comparator>
class unguarded_iterator;
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<(unguarded_iterator<RandomAccessIterator, Comparator>& bi1,
unguarded_iterator<RandomAccessIterator, Comparator>& bi2);
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<=(unguarded_iterator<RandomAccessIterator, Comparator>& bi1,
unguarded_iterator<RandomAccessIterator, Comparator>& bi2);
template<typename RandomAccessIterator, typename Comparator>
class unguarded_iterator
{
private:
/** @brief Current iterator position. */
RandomAccessIterator current;
/** @brief Comparator. */
mutable Comparator& comp;
public:
/** @brief Constructor. Sets iterator to beginning of sequence.
* @param begin Begin iterator of sequence.
* @param end Unused, only for compatibility.
* @param comp Unused, only for compatibility. */
unguarded_iterator(RandomAccessIterator begin,
RandomAccessIterator end, Comparator& comp)
: current(begin), comp(comp)
{ }
/** @brief Pre-increment operator.
* @return This. */
unguarded_iterator<RandomAccessIterator, Comparator>&
operator++()
{
++current;
return *this;
}
/** @brief Dereference operator.
* @return Referenced element. */
typename std::iterator_traits<RandomAccessIterator>::value_type&
operator*()
{ return *current; }
/** @brief Convert to wrapped iterator.
* @return Wrapped iterator. */
operator RandomAccessIterator()
{ return current; }
friend bool
operator< <RandomAccessIterator, Comparator>(
unguarded_iterator<RandomAccessIterator, Comparator>& bi1,
unguarded_iterator<RandomAccessIterator, Comparator>& bi2);
friend bool
operator<= <RandomAccessIterator, Comparator>(
unguarded_iterator<RandomAccessIterator, Comparator>& bi1,
unguarded_iterator<RandomAccessIterator, Comparator>& bi2);
};
/** @brief Compare two elements referenced by unguarded iterators.
* @param bi1 First iterator.
* @param bi2 Second iterator.
* @return @c True if less. */
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<(unguarded_iterator<RandomAccessIterator, Comparator>& bi1,
unguarded_iterator<RandomAccessIterator, Comparator>& bi2)
{
// Normal compare.
return (bi1.comp)(*bi1, *bi2);
}
/** @brief Compare two elements referenced by unguarded iterators.
* @param bi1 First iterator.
* @param bi2 Second iterator.
* @return @c True if less equal. */
template<typename RandomAccessIterator, typename Comparator>
inline bool
operator<=(unguarded_iterator<RandomAccessIterator, Comparator>& bi1,
unguarded_iterator<RandomAccessIterator, Comparator>& bi2)
{
// Normal compare.
return !(bi1.comp)(*bi2, *bi1);
}
/** @brief Highly efficient 3-way merging procedure.
*
* Merging is done with the algorithm implementation described by Peter
* Sanders. Basically, the idea is to minimize the number of necessary
* comparison after merging out an element. The implementation trick
* that makes this fast is that the order of the sequences is stored
* in the instruction pointer (translated into labels in C++).
*
* This works well for merging up to 4 sequences.
*
* Note that making the merging stable does <em>not</em> come at a
* performance hit.
*
* Whether the merging is done guarded or unguarded is selected by the
* used iterator class.
*
* @param seqs_begin Begin iterator of iterator pair input sequence.
* @param seqs_end End iterator of iterator pair input sequence.
* @param target Begin iterator out output sequence.
* @param comp Comparator.
* @param length Maximum length to merge, less equal than the
* total number of elements available.
*
* @return End iterator of output sequence.
*/
template<template<typename RAI, typename C> class iterator,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
RandomAccessIterator3
multiway_merge_3_variant(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
_DifferenceTp length, Comparator comp)
{
_GLIBCXX_CALL(length);
typedef _DifferenceTp difference_type;
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
if (length == 0)
return target;
#if _GLIBCXX_ASSERTIONS
_DifferenceTp orig_length = length;
#endif
iterator<RandomAccessIterator1, Comparator>
seq0(seqs_begin[0].first, seqs_begin[0].second, comp),
seq1(seqs_begin[1].first, seqs_begin[1].second, comp),
seq2(seqs_begin[2].first, seqs_begin[2].second, comp);
if (seq0 <= seq1)
{
if (seq1 <= seq2)
goto s012;
else
if (seq2 < seq0)
goto s201;
else
goto s021;
}
else
{
if (seq1 <= seq2)
{
if (seq0 <= seq2)
goto s102;
else
goto s120;
}
else
goto s210;
}
#define _GLIBCXX_PARALLEL_MERGE_3_CASE(a,b,c,c0,c1) \
s ## a ## b ## c : \
*target = *seq ## a; \
++target; \
--length; \
++seq ## a; \
if (length == 0) goto finish; \
if (seq ## a c0 seq ## b) goto s ## a ## b ## c; \
if (seq ## a c1 seq ## c) goto s ## b ## a ## c; \
goto s ## b ## c ## a;
_GLIBCXX_PARALLEL_MERGE_3_CASE(0, 1, 2, <=, <=);
_GLIBCXX_PARALLEL_MERGE_3_CASE(1, 2, 0, <=, < );
_GLIBCXX_PARALLEL_MERGE_3_CASE(2, 0, 1, < , < );
_GLIBCXX_PARALLEL_MERGE_3_CASE(1, 0, 2, < , <=);
_GLIBCXX_PARALLEL_MERGE_3_CASE(0, 2, 1, <=, <=);
_GLIBCXX_PARALLEL_MERGE_3_CASE(2, 1, 0, < , < );
#undef _GLIBCXX_PARALLEL_MERGE_3_CASE
finish:
;
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(
((RandomAccessIterator1)seq0 - seqs_begin[0].first) +
((RandomAccessIterator1)seq1 - seqs_begin[1].first) +
((RandomAccessIterator1)seq2 - seqs_begin[2].first)
== orig_length);
#endif
seqs_begin[0].first = seq0;
seqs_begin[1].first = seq1;
seqs_begin[2].first = seq2;
return target;
}
/**
* @brief Highly efficient 4-way merging procedure.
*
* Merging is done with the algorithm implementation described by Peter
* Sanders. Basically, the idea is to minimize the number of necessary
* comparison after merging out an element. The implementation trick
* that makes this fast is that the order of the sequences is stored
* in the instruction pointer (translated into goto labels in C++).
*
* This works well for merging up to 4 sequences.
*
* Note that making the merging stable does <em>not</em> come at a
* performance hit.
*
* Whether the merging is done guarded or unguarded is selected by the
* used iterator class.
*
* @param seqs_begin Begin iterator of iterator pair input sequence.
* @param seqs_end End iterator of iterator pair input sequence.
* @param target Begin iterator out output sequence.
* @param comp Comparator.
* @param length Maximum length to merge, less equal than the
* total number of elements available.
*
* @return End iterator of output sequence.
*/
template<template<typename RAI, typename C> class iterator,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
RandomAccessIterator3
multiway_merge_4_variant(RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
_DifferenceTp length, Comparator comp)
{
_GLIBCXX_CALL(length);
typedef _DifferenceTp difference_type;
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
iterator<RandomAccessIterator1, Comparator>
seq0(seqs_begin[0].first, seqs_begin[0].second, comp),
seq1(seqs_begin[1].first, seqs_begin[1].second, comp),
seq2(seqs_begin[2].first, seqs_begin[2].second, comp),
seq3(seqs_begin[3].first, seqs_begin[3].second, comp);
#define _GLIBCXX_PARALLEL_DECISION(a,b,c,d) { \
if (seq ## d < seq ## a) goto s ## d ## a ## b ## c; \
if (seq ## d < seq ## b) goto s ## a ## d ## b ## c; \
if (seq ## d < seq ## c) goto s ## a ## b ## d ## c; \
goto s ## a ## b ## c ## d; }
if (seq0 <= seq1)
{
if (seq1 <= seq2)
_GLIBCXX_PARALLEL_DECISION(0,1,2,3)
else
if (seq2 < seq0)
_GLIBCXX_PARALLEL_DECISION(2,0,1,3)
else
_GLIBCXX_PARALLEL_DECISION(0,2,1,3)
}
else
{
if (seq1 <= seq2)
{
if (seq0 <= seq2)
_GLIBCXX_PARALLEL_DECISION(1,0,2,3)
else
_GLIBCXX_PARALLEL_DECISION(1,2,0,3)
}
else
_GLIBCXX_PARALLEL_DECISION(2,1,0,3)
}
#define _GLIBCXX_PARALLEL_MERGE_4_CASE(a,b,c,d,c0,c1,c2) \
s ## a ## b ## c ## d: \
if (length == 0) goto finish; \
*target = *seq ## a; \
++target; \
--length; \
++seq ## a; \
if (seq ## a c0 seq ## b) goto s ## a ## b ## c ## d; \
if (seq ## a c1 seq ## c) goto s ## b ## a ## c ## d; \
if (seq ## a c2 seq ## d) goto s ## b ## c ## a ## d; \
goto s ## b ## c ## d ## a;
_GLIBCXX_PARALLEL_MERGE_4_CASE(0, 1, 2, 3, <=, <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(0, 1, 3, 2, <=, <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(0, 2, 1, 3, <=, <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(0, 2, 3, 1, <=, <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(0, 3, 1, 2, <=, <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(0, 3, 2, 1, <=, <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(1, 0, 2, 3, < , <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(1, 0, 3, 2, < , <=, <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(1, 2, 0, 3, <=, < , <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(1, 2, 3, 0, <=, <=, < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(1, 3, 0, 2, <=, < , <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(1, 3, 2, 0, <=, <=, < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(2, 0, 1, 3, < , < , <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(2, 0, 3, 1, < , <=, < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(2, 1, 0, 3, < , < , <=);
_GLIBCXX_PARALLEL_MERGE_4_CASE(2, 1, 3, 0, < , <=, < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(2, 3, 0, 1, <=, < , < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(2, 3, 1, 0, <=, < , < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(3, 0, 1, 2, < , < , < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(3, 0, 2, 1, < , < , < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(3, 1, 0, 2, < , < , < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(3, 1, 2, 0, < , < , < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(3, 2, 0, 1, < , < , < );
_GLIBCXX_PARALLEL_MERGE_4_CASE(3, 2, 1, 0, < , < , < );
#undef _GLIBCXX_PARALLEL_MERGE_4_CASE
#undef _GLIBCXX_PARALLEL_DECISION
finish:
;
seqs_begin[0].first = seq0;
seqs_begin[1].first = seq1;
seqs_begin[2].first = seq2;
seqs_begin[3].first = seq3;
return target;
}
/** @brief Multi-way merging procedure for a high branching factor,
* guarded case.
*
* This merging variant uses a LoserTree class as selected by <tt>LT</tt>.
*
* Stability is selected through the used LoserTree class <tt>LT</tt>.
*
* At least one non-empty sequence is required.
*
* @param seqs_begin Begin iterator of iterator pair input sequence.
* @param seqs_end End iterator of iterator pair input sequence.
* @param target Begin iterator out output sequence.
* @param comp Comparator.
* @param length Maximum length to merge, less equal than the
* total number of elements available.
*
* @return End iterator of output sequence.
*/
template<typename LT,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
RandomAccessIterator3
multiway_merge_loser_tree(RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
_DifferenceTp length, Comparator comp)
{
_GLIBCXX_CALL(length)
typedef _DifferenceTp difference_type;
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
int k = static_cast<int>(seqs_end - seqs_begin);
LT lt(k, comp);
// Default value for potentially non-default-constructible types.
value_type* arbitrary_element = NULL;
for (int t = 0; t < k; ++t)
{
if(arbitrary_element == NULL
&& _GLIBCXX_PARALLEL_LENGTH(seqs_begin[t]) > 0)
arbitrary_element = &(*seqs_begin[t].first);
}
for (int t = 0; t < k; ++t)
{
if (seqs_begin[t].first == seqs_begin[t].second)
lt.insert_start(*arbitrary_element, t, true);
else
lt.insert_start(*seqs_begin[t].first, t, false);
}
lt.init();
int source;
for (difference_type i = 0; i < length; ++i)
{
//take out
source = lt.get_min_source();
*(target++) = *(seqs_begin[source].first++);
// Feed.
if (seqs_begin[source].first == seqs_begin[source].second)
lt.delete_min_insert(*arbitrary_element, true);
else
// Replace from same source.
lt.delete_min_insert(*seqs_begin[source].first, false);
}
return target;
}
/** @brief Multi-way merging procedure for a high branching factor,
* unguarded case.
*
* Merging is done using the LoserTree class <tt>LT</tt>.
*
* Stability is selected by the used LoserTrees.
*
* @pre No input will run out of elements during the merge.
*
* @param seqs_begin Begin iterator of iterator pair input sequence.
* @param seqs_end End iterator of iterator pair input sequence.
* @param target Begin iterator out output sequence.
* @param comp Comparator.
* @param length Maximum length to merge, less equal than the
* total number of elements available.
*
* @return End iterator of output sequence.
*/
template<typename LT,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp, typename Comparator>
RandomAccessIterator3
multiway_merge_loser_tree_unguarded(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
const typename std::iterator_traits<typename std::iterator_traits<
RandomAccessIteratorIterator>::value_type::first_type>::value_type&
sentinel,
_DifferenceTp length,
Comparator comp)
{
_GLIBCXX_CALL(length)
typedef _DifferenceTp difference_type;
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
int k = seqs_end - seqs_begin;
LT lt(k, sentinel, comp);
for (int t = 0; t < k; ++t)
{
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(seqs_begin[t].first != seqs_begin[t].second);
#endif
lt.insert_start(*seqs_begin[t].first, t, false);
}
lt.init();
int source;
#if _GLIBCXX_ASSERTIONS
difference_type i = 0;
#endif
RandomAccessIterator3 target_end = target + length;
while (target < target_end)
{
// Take out.
source = lt.get_min_source();
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(0 <= source && source < k);
_GLIBCXX_PARALLEL_ASSERT(i == 0
|| !comp(*(seqs_begin[source].first), *(target - 1)));
#endif
// Feed.
*(target++) = *(seqs_begin[source].first++);
#if _GLIBCXX_ASSERTIONS
++i;
#endif
// Replace from same source.
lt.delete_min_insert(*seqs_begin[source].first, false);
}
return target;
}
/** @brief Multi-way merging procedure for a high branching factor,
* requiring sentinels to exist.
*
* @param stable The value must the same as for the used LoserTrees.
* @param UnguardedLoserTree Loser Tree variant to use for the unguarded
* merging.
* @param GuardedLoserTree Loser Tree variant to use for the guarded
* merging.
*
* @param seqs_begin Begin iterator of iterator pair input sequence.
* @param seqs_end End iterator of iterator pair input sequence.
* @param target Begin iterator out output sequence.
* @param comp Comparator.
* @param length Maximum length to merge, less equal than the
* total number of elements available.
*
* @return End iterator of output sequence.
*/
template<
typename UnguardedLoserTree,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
RandomAccessIterator3
multiway_merge_loser_tree_sentinel(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
const typename std::iterator_traits<typename std::iterator_traits<
RandomAccessIteratorIterator>::value_type::first_type>::value_type&
sentinel,
_DifferenceTp length,
Comparator comp)
{
_GLIBCXX_CALL(length)
typedef _DifferenceTp difference_type;
typedef std::iterator_traits<RandomAccessIteratorIterator> traits_type;
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
RandomAccessIterator3 target_end;
for (RandomAccessIteratorIterator s = seqs_begin; s != seqs_end; ++s)
// Move the sequends end behind the sentinel spots. This has the
// effect that the sentinel appears to be within the sequence. Then,
// we can use the unguarded variant if we merge out as many
// non-sentinel elements as we have.
++((*s).second);
target_end = multiway_merge_loser_tree_unguarded
<UnguardedLoserTree>
(seqs_begin, seqs_end, target, sentinel, length, comp);
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(target_end == target + length);
_GLIBCXX_PARALLEL_ASSERT(is_sorted(target, target_end, comp));
#endif
// Restore the sequence ends so the sentinels are not contained in the
// sequence any more (see comment in loop above).
for (RandomAccessIteratorIterator s = seqs_begin; s != seqs_end; ++s)
--((*s).second);
return target_end;
}
/**
* @brief Traits for determining whether the loser tree should
* use pointers or copies.
*
* The field "use_pointer" is used to determine whether to use pointers in
* the loser trees or whether to copy the values into the loser tree.
*
* The default behavior is to use pointers if the data type is 4 times as
* big as the pointer to it.
*
* Specialize for your data type to customize the behavior.
*
* Example:
*
* template<>
* struct loser_tree_traits<int>
* { static const bool use_pointer = false; };
*
* template<>
* struct loser_tree_traits<heavyweight_type>
* { static const bool use_pointer = true; };
*
* @param T type to give the loser tree traits for.
*/
template <typename T>
struct loser_tree_traits
{
/**
* @brief True iff to use pointers instead of values in loser trees.
*
* The default behavior is to use pointers if the data type is four
* times as big as the pointer to it.
*/
static const bool use_pointer = (sizeof(T) > 4 * sizeof(T*));
};
/**
* @brief Switch for 3-way merging with sentinels turned off.
*
* Note that 3-way merging is always stable!
*/
template<
bool sentinels /*default == false*/,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
struct multiway_merge_3_variant_sentinel_switch
{
RandomAccessIterator3 operator()(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
_DifferenceTp length, Comparator comp)
{
return multiway_merge_3_variant<guarded_iterator>(
seqs_begin, seqs_end, target, length, comp);
}
};
/**
* @brief Switch for 3-way merging with sentinels turned on.
*
* Note that 3-way merging is always stable!
*/
template<
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
struct multiway_merge_3_variant_sentinel_switch
<true, RandomAccessIteratorIterator, RandomAccessIterator3,
_DifferenceTp, Comparator>
{
RandomAccessIterator3 operator()(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
_DifferenceTp length, Comparator comp)
{
return multiway_merge_3_variant<unguarded_iterator>(
seqs_begin, seqs_end, target, length, comp);
}
};
/**
* @brief Switch for 4-way merging with sentinels turned off.
*
* Note that 4-way merging is always stable!
*/
template<
bool sentinels /*default == false*/,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
struct multiway_merge_4_variant_sentinel_switch
{
RandomAccessIterator3 operator()(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
_DifferenceTp length, Comparator comp)
{
return multiway_merge_4_variant<guarded_iterator>(
seqs_begin, seqs_end, target, length, comp);
}
};
/**
* @brief Switch for 4-way merging with sentinels turned on.
*
* Note that 4-way merging is always stable!
*/
template<
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
struct multiway_merge_4_variant_sentinel_switch
<true, RandomAccessIteratorIterator, RandomAccessIterator3,
_DifferenceTp, Comparator>
{
RandomAccessIterator3 operator()(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
_DifferenceTp length, Comparator comp)
{
return multiway_merge_4_variant<unguarded_iterator>(
seqs_begin, seqs_end, target, length, comp);
}
};
/**
* @brief Switch for k-way merging with sentinels turned on.
*/
template<
bool sentinels,
bool stable,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
struct multiway_merge_k_variant_sentinel_switch
{
RandomAccessIterator3 operator()(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
const typename std::iterator_traits<typename std::iterator_traits<
RandomAccessIteratorIterator>::value_type::first_type>::value_type&
sentinel,
_DifferenceTp length, Comparator comp)
{
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
return multiway_merge_loser_tree_sentinel<
typename __gnu_cxx::__conditional_type<
loser_tree_traits<value_type>::use_pointer
, LoserTreePointerUnguarded<stable, value_type, Comparator>
, LoserTreeUnguarded<stable, value_type, Comparator>
>::__type>(seqs_begin, seqs_end, target, sentinel, length, comp);
}
};
/**
* @brief Switch for k-way merging with sentinels turned off.
*/
template<
bool stable,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
struct multiway_merge_k_variant_sentinel_switch
<false, stable, RandomAccessIteratorIterator, RandomAccessIterator3,
_DifferenceTp, Comparator>
{
RandomAccessIterator3 operator()(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
const typename std::iterator_traits<typename std::iterator_traits<
RandomAccessIteratorIterator>::value_type::first_type>::value_type&
sentinel,
_DifferenceTp length, Comparator comp)
{
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
return multiway_merge_loser_tree<
typename __gnu_cxx::__conditional_type<
loser_tree_traits<value_type>::use_pointer
, LoserTreePointer<stable, value_type, Comparator>
, LoserTree<stable, value_type, Comparator>
>::__type >(seqs_begin, seqs_end, target, length, comp);
}
};
/** @brief Sequential multi-way merging switch.
*
* The _GLIBCXX_PARALLEL_DECISION is based on the branching factor and
* runtime settings.
* @param seqs_begin Begin iterator of iterator pair input sequence.
* @param seqs_end End iterator of iterator pair input sequence.
* @param target Begin iterator out output sequence.
* @param comp Comparator.
* @param length Maximum length to merge, possibly larger than the
* number of elements available.
* @param stable Stable merging incurs a performance penalty.
* @param sentinel The sequences have a sentinel element.
* @return End iterator of output sequence. */
template<
bool stable,
bool sentinels,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Comparator>
RandomAccessIterator3
sequential_multiway_merge(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
const typename std::iterator_traits<typename std::iterator_traits<
RandomAccessIteratorIterator>::value_type::first_type>::value_type&
sentinel,
_DifferenceTp length, Comparator comp)
{
_GLIBCXX_CALL(length)
typedef _DifferenceTp difference_type;
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
#if _GLIBCXX_ASSERTIONS
for (RandomAccessIteratorIterator s = seqs_begin; s != seqs_end; ++s)
{
_GLIBCXX_PARALLEL_ASSERT(is_sorted((*s).first, (*s).second, comp));
}
#endif
_DifferenceTp total_length = 0;
for (RandomAccessIteratorIterator s = seqs_begin; s != seqs_end; ++s)
total_length += _GLIBCXX_PARALLEL_LENGTH(*s);
length = std::min<_DifferenceTp>(length, total_length);
if(length == 0)
return target;
RandomAccessIterator3 return_target = target;
int k = static_cast<int>(seqs_end - seqs_begin);
switch (k)
{
case 0:
break;
case 1:
return_target = std::copy(seqs_begin[0].first,
seqs_begin[0].first + length,
target);
seqs_begin[0].first += length;
break;
case 2:
return_target = merge_advance(seqs_begin[0].first,
seqs_begin[0].second,
seqs_begin[1].first,
seqs_begin[1].second,
target, length, comp);
break;
case 3:
return_target = multiway_merge_3_variant_sentinel_switch<
sentinels
, RandomAccessIteratorIterator
, RandomAccessIterator3
, _DifferenceTp
, Comparator>()(seqs_begin, seqs_end, target, length, comp);
break;
case 4:
return_target = multiway_merge_4_variant_sentinel_switch<
sentinels
, RandomAccessIteratorIterator
, RandomAccessIterator3
, _DifferenceTp
, Comparator>()(seqs_begin, seqs_end, target, length, comp);
break;
default:
return_target = multiway_merge_k_variant_sentinel_switch<
sentinels
, stable
, RandomAccessIteratorIterator
, RandomAccessIterator3
, _DifferenceTp
, Comparator>()(seqs_begin, seqs_end, target, sentinel, length, comp);
break;
}
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(is_sorted(target, target + length, comp));
#endif
return return_target;
}
/**
* @brief Stable sorting functor.
*
* Used to reduce code instanciation in multiway_merge_sampling_splitting.
*/
template<bool stable, class RandomAccessIterator, class StrictWeakOrdering>
struct sampling_sorter
{
void operator()(RandomAccessIterator first, RandomAccessIterator last,
StrictWeakOrdering comp)
{ __gnu_sequential::stable_sort(first, last, comp); }
};
/**
* @brief Non-stable sorting functor.
*
* Used to reduce code instantiation in multiway_merge_sampling_splitting.
*/
template<class RandomAccessIterator, class StrictWeakOrdering>
struct sampling_sorter<false, RandomAccessIterator, StrictWeakOrdering>
{
void operator()(RandomAccessIterator first, RandomAccessIterator last,
StrictWeakOrdering comp)
{ __gnu_sequential::sort(first, last, comp); }
};
/**
* @brief Sampling based splitting for parallel multiway-merge routine.
*/
template<
bool stable
, typename RandomAccessIteratorIterator
, typename Comparator
, typename difference_type>
void multiway_merge_sampling_splitting(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
difference_type length, difference_type total_length, Comparator comp,
std::vector<std::pair<difference_type, difference_type> > *pieces)
{
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type;
// k sequences.
int k = static_cast<int>(seqs_end - seqs_begin);
int num_threads = omp_get_num_threads();
difference_type num_samples =
__gnu_parallel::_Settings::get().merge_oversampling * num_threads;
value_type* samples = static_cast<value_type*>(
::operator new(sizeof(value_type) * k * num_samples));
// Sample.
for (int s = 0; s < k; ++s)
for (difference_type i = 0; i < num_samples; ++i)
{
difference_type sample_index =
static_cast<difference_type>(
_GLIBCXX_PARALLEL_LENGTH(seqs_begin[s])
* (double(i + 1) / (num_samples + 1))
* (double(length) / total_length));
new(&(samples[s * num_samples + i]))
value_type(seqs_begin[s].first[sample_index]);
}
// Sort stable or non-stable, depending on value of template parameter
// "stable".
sampling_sorter<stable, value_type*, Comparator>()(
samples, samples + (num_samples * k), comp);
for (int slab = 0; slab < num_threads; ++slab)
// For each slab / processor.
for (int seq = 0; seq < k; ++seq)
{
// For each sequence.
if (slab > 0)
pieces[slab][seq].first =
std::upper_bound(
seqs_begin[seq].first,
seqs_begin[seq].second,
samples[num_samples * k * slab / num_threads],
comp)
- seqs_begin[seq].first;
else
// Absolute beginning.
pieces[slab][seq].first = 0;
if ((slab + 1) < num_threads)
pieces[slab][seq].second =
std::upper_bound(
seqs_begin[seq].first,
seqs_begin[seq].second,
samples[num_samples * k * (slab + 1) /
num_threads], comp)
- seqs_begin[seq].first;
else
// Absolute end.
pieces[slab][seq].second = _GLIBCXX_PARALLEL_LENGTH(seqs_begin[seq]);
}
::operator delete(samples);
}
/**
* @brief Exact splitting for parallel multiway-merge routine.
*
* None of the passed sequences may be empty.
*/
template<
bool stable
, typename RandomAccessIteratorIterator
, typename Comparator
, typename difference_type>
void multiway_merge_exact_splitting(
RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
difference_type length, difference_type total_length, Comparator comp,
std::vector<std::pair<difference_type, difference_type> > *pieces)
{
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
const bool tight = (total_length == length);
// k sequences.
const int k = static_cast<int>(seqs_end - seqs_begin);
const int num_threads = omp_get_num_threads();
// (Settings::multiway_merge_splitting == __gnu_parallel::_Settings::EXACT).
std::vector<RandomAccessIterator1>* offsets =
new std::vector<RandomAccessIterator1>[num_threads];
std::vector<
std::pair<RandomAccessIterator1, RandomAccessIterator1>
> se(k);
copy(seqs_begin, seqs_end, se.begin());
difference_type* borders =
new difference_type[num_threads + 1];
equally_split(length, num_threads, borders);
for (int s = 0; s < (num_threads - 1); ++s)
{
offsets[s].resize(k);
multiseq_partition(
se.begin(), se.end(), borders[s + 1],
offsets[s].begin(), comp);
// Last one also needed and available.
if (!tight)
{
offsets[num_threads - 1].resize(k);
multiseq_partition(se.begin(), se.end(),
difference_type(length),
offsets[num_threads - 1].begin(), comp);
}
}
delete[] borders;
for (int slab = 0; slab < num_threads; ++slab)
{
// For each slab / processor.
for (int seq = 0; seq < k; ++seq)
{
// For each sequence.
if (slab == 0)
{
// Absolute beginning.
pieces[slab][seq].first = 0;
}
else
pieces[slab][seq].first =
pieces[slab - 1][seq].second;
if (!tight || slab < (num_threads - 1))
pieces[slab][seq].second =
offsets[slab][seq] - seqs_begin[seq].first;
else
{
// slab == num_threads - 1
pieces[slab][seq].second =
_GLIBCXX_PARALLEL_LENGTH(seqs_begin[seq]);
}
}
}
delete[] offsets;
}
/** @brief Parallel multi-way merge routine.
*
* The _GLIBCXX_PARALLEL_DECISION is based on the branching factor
* and runtime settings.
*
* Must not be called if the number of sequences is 1.
*
* @param Splitter functor to split input (either exact or sampling based)
*
* @param seqs_begin Begin iterator of iterator pair input sequence.
* @param seqs_end End iterator of iterator pair input sequence.
* @param target Begin iterator out output sequence.
* @param comp Comparator.
* @param length Maximum length to merge, possibly larger than the
* number of elements available.
* @param stable Stable merging incurs a performance penalty.
* @param sentinel Ignored.
* @return End iterator of output sequence.
*/
template<
bool stable,
bool sentinels,
typename RandomAccessIteratorIterator,
typename RandomAccessIterator3,
typename _DifferenceTp,
typename Splitter,
typename Comparator
>
RandomAccessIterator3
parallel_multiway_merge(RandomAccessIteratorIterator seqs_begin,
RandomAccessIteratorIterator seqs_end,
RandomAccessIterator3 target,
Splitter splitter,
_DifferenceTp length,
Comparator comp,
thread_index_t num_threads)
{
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(seqs_end - seqs_begin > 1);
#endif
_GLIBCXX_CALL(length)
typedef _DifferenceTp difference_type;
typedef typename std::iterator_traits<RandomAccessIteratorIterator>
::value_type::first_type
RandomAccessIterator1;
typedef typename
std::iterator_traits<RandomAccessIterator1>::value_type value_type;
// Leave only non-empty sequences.
typedef std::pair<RandomAccessIterator1, RandomAccessIterator1> seq_type;
seq_type* ne_seqs = new seq_type[seqs_end - seqs_begin];
int k = 0;
difference_type total_length = 0;
for (RandomAccessIteratorIterator raii = seqs_begin;
raii != seqs_end; ++raii)
{
_DifferenceTp seq_length = _GLIBCXX_PARALLEL_LENGTH(*raii);
if(seq_length > 0)
{
total_length += seq_length;
ne_seqs[k++] = *raii;
}
}
_GLIBCXX_CALL(total_length)
length = std::min<_DifferenceTp>(length, total_length);
if (total_length == 0 || k == 0)
{
delete[] ne_seqs;
return target;
}
std::vector<std::pair<difference_type, difference_type> >* pieces;
num_threads = static_cast<thread_index_t>
(std::min<difference_type>(num_threads, total_length));
# pragma omp parallel num_threads (num_threads)
{
# pragma omp single
{
num_threads = omp_get_num_threads();
// Thread t will have to merge pieces[iam][0..k - 1]
pieces = new std::vector<
std::pair<difference_type, difference_type> >[num_threads];
for (int s = 0; s < num_threads; ++s)
pieces[s].resize(k);
difference_type num_samples =
__gnu_parallel::_Settings::get().merge_oversampling *
num_threads;
splitter(ne_seqs, ne_seqs + k, length, total_length,
comp, pieces);
} //single
thread_index_t iam = omp_get_thread_num();
difference_type target_position = 0;
for (int c = 0; c < k; ++c)
target_position += pieces[iam][c].first;
seq_type* chunks = new seq_type[k];
for (int s = 0; s < k; ++s)
{
chunks[s] = std::make_pair(
ne_seqs[s].first + pieces[iam][s].first,
ne_seqs[s].first + pieces[iam][s].second);
}
if(length > target_position)
sequential_multiway_merge<stable, sentinels>(
chunks, chunks + k, target + target_position,
*(seqs_begin->second), length - target_position, comp);
delete[] chunks;
} // parallel
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(is_sorted(target, target + length, comp));
#endif
k = 0;
// Update ends of sequences.
for (RandomAccessIteratorIterator raii = seqs_begin;
raii != seqs_end; ++raii)
{
_DifferenceTp length = _GLIBCXX_PARALLEL_LENGTH(*raii);
if(length > 0)
(*raii).first += pieces[num_threads - 1][k++].second;
}
delete[] pieces;
delete[] ne_seqs;
return target + length;
}
/**
* @brief Multiway Merge Frontend.
*
* Merge the sequences specified by seqs_begin and seqs_end into
* target. seqs_begin and seqs_end must point to a sequence of
* pairs. These pairs must contain an iterator to the beginning
* of a sequence in their first entry and an iterator the end of
* the same sequence in their second entry.
*
* Ties are broken arbitrarily. See stable_multiway_merge for a variant
* that breaks ties by sequence number but is slower.
*
* The first entries of the pairs (i.e. the begin iterators) will be moved
* forward.
*
* The output sequence has to provide enough space for all elements
* that are written to it.
*
* This function will merge the input sequences:
*
* - not stable
* - parallel, depending on the input size and Settings
* - using sampling for splitting
* - not using sentinels
*
* Example:
*
* <pre>
* int sequences[10][10];
* for (int i = 0; i < 10; ++i)
* for (int j = 0; i < 10; ++j)
* sequences[i][j] = j;
*
* int out[33];
* std::vector<std::pair<int*> > seqs;
* for (int i = 0; i < 10; ++i)
* { seqs.push(std::make_pair<int*>(sequences[i], sequences[i] + 10)) }
*
* multiway_merge(seqs.begin(), seqs.end(), target, std::less<int>(), 33);
* </pre>
*
* @see stable_multiway_merge
*
* @pre All input sequences must be sorted.
* @pre Target must provide enough space to merge out length elements or
* the number of elements in all sequences, whichever is smaller.
*
* @post [target, return value) contains merged elements from the
* input sequences.
* @post return value - target = min(length, number of elements in all
* sequences).
*
* @param RandomAccessIteratorPairIterator iterator over sequence
* of pairs of iterators
* @param RandomAccessIteratorOut iterator over target sequence
* @param _DifferenceTp difference type for the sequence
* @param Comparator strict weak ordering type to compare elements
* in sequences
*
* @param seqs_begin begin of sequence sequence
* @param seqs_end end of sequence sequence
* @param target target sequence to merge to.
* @param comp strict weak ordering to use for element comparison.
* @param length Maximum length to merge, possibly larger than the
* number of elements available.
*
* @return end iterator of output sequence
*/
// multiway_merge
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::sequential_tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute multiway merge *sequentially*.
return sequential_multiway_merge
</* stable = */ false, /* sentinels = */ false>
(seqs_begin, seqs_end, target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::exact_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ false, /* sentinels = */ false>(
seqs_begin, seqs_end, target,
multiway_merge_exact_splitting</* stable = */ false,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge
</* stable = */ false, /* sentinels = */ false>(
seqs_begin, seqs_end, target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::sampling_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ false, /* sentinels = */ false>(
seqs_begin, seqs_end,
target,
multiway_merge_exact_splitting</* stable = */ false,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge
</* stable = */ false, /* sentinels = */ false>(
seqs_begin, seqs_end,
target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, parallel_tag tag = parallel_tag(0))
{
return multiway_merge(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, default_parallel_tag tag)
{
return multiway_merge(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
// stable_multiway_merge
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::sequential_tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute multiway merge *sequentially*.
return sequential_multiway_merge
</* stable = */ true, /* sentinels = */ false>
(seqs_begin, seqs_end, target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::exact_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ true, /* sentinels = */ false>(
seqs_begin, seqs_end,
target,
multiway_merge_exact_splitting</* stable = */ true,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge</* stable = */ true,
/* sentinels = */ false>(
seqs_begin, seqs_end,
target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, sampling_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ true, /* sentinels = */ false>(
seqs_begin, seqs_end,
target,
multiway_merge_sampling_splitting</* stable = */ true,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge
</* stable = */ true, /* sentinels = */ false>(
seqs_begin, seqs_end,
target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, parallel_tag tag = parallel_tag(0))
{
return stable_multiway_merge(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, default_parallel_tag tag)
{
return stable_multiway_merge(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
/**
* @brief Multiway Merge Frontend.
*
* Merge the sequences specified by seqs_begin and seqs_end into
* target. seqs_begin and seqs_end must point to a sequence of
* pairs. These pairs must contain an iterator to the beginning
* of a sequence in their first entry and an iterator the end of
* the same sequence in their second entry.
*
* Ties are broken arbitrarily. See stable_multiway_merge for a variant
* that breaks ties by sequence number but is slower.
*
* The first entries of the pairs (i.e. the begin iterators) will be moved
* forward accordingly.
*
* The output sequence has to provide enough space for all elements
* that are written to it.
*
* This function will merge the input sequences:
*
* - not stable
* - parallel, depending on the input size and Settings
* - using sampling for splitting
* - using sentinels
*
* You have to take care that the element the end iterator points to is
* readable and contains a value that is greater than any other non-sentinel
* value in all sequences.
*
* Example:
*
* <pre>
* int sequences[10][11];
* for (int i = 0; i < 10; ++i)
* for (int j = 0; i < 11; ++j)
* sequences[i][j] = j; // last one is sentinel!
*
* int out[33];
* std::vector<std::pair<int*> > seqs;
* for (int i = 0; i < 10; ++i)
* { seqs.push(std::make_pair<int*>(sequences[i], sequences[i] + 10)) }
*
* multiway_merge(seqs.begin(), seqs.end(), target, std::less<int>(), 33);
* </pre>
*
* @pre All input sequences must be sorted.
* @pre Target must provide enough space to merge out length elements or
* the number of elements in all sequences, whichever is smaller.
* @pre For each @c i, @c seqs_begin[i].second must be the end
* marker of the sequence, but also reference the one more sentinel
* element.
*
* @post [target, return value) contains merged elements from the
* input sequences.
* @post return value - target = min(length, number of elements in all
* sequences).
*
* @see stable_multiway_merge_sentinels
*
* @param RandomAccessIteratorPairIterator iterator over sequence
* of pairs of iterators
* @param RandomAccessIteratorOut iterator over target sequence
* @param _DifferenceTp difference type for the sequence
* @param Comparator strict weak ordering type to compare elements
* in sequences
*
* @param seqs_begin begin of sequence sequence
* @param seqs_end end of sequence sequence
* @param target target sequence to merge to.
* @param comp strict weak ordering to use for element comparison.
* @param length Maximum length to merge, possibly larger than the
* number of elements available.
*
* @return end iterator of output sequence
*/
// multiway_merge_sentinels
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::sequential_tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute multiway merge *sequentially*.
return sequential_multiway_merge
</* stable = */ false, /* sentinels = */ true>
(seqs_begin, seqs_end,
target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::exact_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ false, /* sentinels = */ true>(
seqs_begin, seqs_end,
target,
multiway_merge_exact_splitting</* stable = */ false,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge
</* stable = */ false, /* sentinels = */ true>(
seqs_begin, seqs_end,
target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, sampling_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ false, /* sentinels = */ true>
(seqs_begin, seqs_end, target,
multiway_merge_sampling_splitting</* stable = */ false,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge
</* stable = */false, /* sentinels = */ true>(
seqs_begin, seqs_end,
target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, parallel_tag tag = parallel_tag(0))
{
return multiway_merge_sentinels(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, default_parallel_tag tag)
{
return multiway_merge_sentinels(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
// stable_multiway_merge_sentinels
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::sequential_tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute multiway merge *sequentially*.
return sequential_multiway_merge
</* stable = */ true, /* sentinels = */ true>
(seqs_begin, seqs_end, target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, __gnu_parallel::exact_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ true, /* sentinels = */ true>(
seqs_begin, seqs_end,
target,
multiway_merge_exact_splitting</* stable = */ true,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge
</* stable = */ true, /* sentinels = */ true>(
seqs_begin, seqs_end, target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, sampling_tag tag)
{
typedef _DifferenceTp difference_type;
_GLIBCXX_CALL(seqs_end - seqs_begin)
// catch special case: no sequences
if (seqs_begin == seqs_end)
return target;
// Execute merge; maybe parallel, depending on the number of merged
// elements and the number of sequences and global thresholds in
// Settings.
if ((seqs_end - seqs_begin > 1) &&
_GLIBCXX_PARALLEL_CONDITION(
((seqs_end - seqs_begin) >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_k)
&& ((sequence_index_t)length >=
__gnu_parallel::_Settings::get().multiway_merge_minimal_n)))
return parallel_multiway_merge
</* stable = */ true, /* sentinels = */ true>(
seqs_begin, seqs_end,
target,
multiway_merge_sampling_splitting</* stable = */ true,
typename std::iterator_traits<RandomAccessIteratorPairIterator>
::value_type*, Comparator, _DifferenceTp>,
static_cast<difference_type>(length), comp, tag.get_num_threads());
else
return sequential_multiway_merge
</* stable = */ true, /* sentinels = */ true>(
seqs_begin, seqs_end,
target, *(seqs_begin->second), length, comp);
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, parallel_tag tag = parallel_tag(0))
{
return stable_multiway_merge_sentinels(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
// public interface
template<
typename RandomAccessIteratorPairIterator
, typename RandomAccessIteratorOut
, typename _DifferenceTp
, typename Comparator>
RandomAccessIteratorOut
stable_multiway_merge_sentinels(RandomAccessIteratorPairIterator seqs_begin
, RandomAccessIteratorPairIterator seqs_end
, RandomAccessIteratorOut target
, _DifferenceTp length, Comparator comp
, default_parallel_tag tag)
{
return stable_multiway_merge_sentinels(seqs_begin, seqs_end, target, length, comp,
exact_tag(tag.get_num_threads()));
}
}; // namespace __gnu_parallel
#endif /* _GLIBCXX_PARALLEL_MULTIWAY_MERGE_H */