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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 */