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/*
* Copyright 2001, 2002 Adrian Thurston <thurston@complang.org>
*/
/* This file is part of Aapl.
*
* Aapl is free software; you can redistribute it and/or modify it under the
* terms of the GNU Lesser General Public License as published by the Free
* Software Foundation; either version 2.1 of the License, or (at your option)
* any later version.
*
* Aapl 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 Lesser General Public License for
* more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with Aapl; if not, write to the Free Software Foundation, Inc., 59
* Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef _AAPL_MERGESORT_H
#define _AAPL_MERGESORT_H
#include "bubblesort.h"
#ifdef AAPL_NAMESPACE
namespace Aapl {
#endif
/**
* \addtogroup sort
* @{
*/
/**
* \class MergeSort
* \brief Merge sort an array of data.
*
* MergeSort can be used to sort any array of objects of type T provided a
* compare class is given. MergeSort is not in-place, it requires temporary
* storage equal to the size of the array. The temporary storage is allocated
* on the heap.
*
* Objects are not made aware that they are being moved around in memory.
* Assignment operators, constructors and destructors are never invoked by the
* sort.
*
* MergeSort runs in worst case O(n*log(n)) time. In most cases it is slower
* than QuickSort because more copying is neccessary. But on the other hand,
* it is a stable sort, meaning that objects with the same key have their
* relative ordering preserved. Also, its worst case is better. MergeSort
* switches to a BubbleSort when the size of the array being sorted is small.
* This happens when directly sorting a small array or when MergeSort calls
* itself recursively on a small portion of a larger array.
*/
/*@}*/
/* MergeSort. */
template <class T, class Compare> class MergeSort
: public BubbleSort<T, Compare>
{
public:
/* Sorting interface routine. */
void sort(T *data, long len);
private:
/* Recursive worker. */
void doSort(T *tmpStor, T *data, long len);
};
#define _MS_BUBBLE_THRESH 16
/* Recursive mergesort worker. Split data, make recursive calls, merge
* results. */
template< class T, class Compare> void MergeSort<T,Compare>::
doSort(T *tmpStor, T *data, long len)
{
if ( len <= 1 )
return;
if ( len <= _MS_BUBBLE_THRESH ) {
BubbleSort<T, Compare>::sort( data, len );
return;
}
long mid = len / 2;
doSort( tmpStor, data, mid );
doSort( tmpStor + mid, data + mid, len - mid );
/* Merge the data. */
T *endLower = data + mid, *lower = data;
T *endUpper = data + len, *upper = data + mid;
T *dest = tmpStor;
while ( true ) {
if ( lower == endLower ) {
/* Possibly upper left. */
if ( upper != endUpper )
memcpy( dest, upper, (endUpper - upper) * sizeof(T) );
break;
}
else if ( upper == endUpper ) {
/* Only lower left. */
if ( lower != endLower )
memcpy( dest, lower, (endLower - lower) * sizeof(T) );
break;
}
else {
/* Both upper and lower left. */
if ( this->compare(*lower, *upper) <= 0 )
memcpy( dest++, lower++, sizeof(T) );
else
memcpy( dest++, upper++, sizeof(T) );
}
}
/* Copy back from the tmpStor array. */
memcpy( data, tmpStor, sizeof( T ) * len );
}
/**
* \brief Merge sort an array of data.
*/
template< class T, class Compare>
void MergeSort<T,Compare>::sort(T *data, long len)
{
/* Allocate the tmp space needed by merge sort, sort and free. */
T *tmpStor = (T*) new char[sizeof(T) * len];
doSort( tmpStor, data, len );
delete[] (char*) tmpStor;
}
#ifdef AAPL_NAMESPACE
}
#endif
#endif /* _AAPL_MERGESORT_H */
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