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/*
* Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#ifndef SHARE_VM_UTILITIES_QUICKSORT_HPP
#define SHARE_VM_UTILITIES_QUICKSORT_HPP
#include "memory/allocation.hpp"
#include "runtime/globals.hpp"
#include "utilities/debug.hpp"
class QuickSort : AllStatic {
private:
template<class T>
static void swap(T* array, int x, int y) {
T tmp = array[x];
array[x] = array[y];
array[y] = tmp;
}
// As pivot we use the median of the first, last and middle elements.
// We swap in these three values at the right place in the array. This
// means that this method not only returns the index of the pivot
// element. It also alters the array so that:
// array[first] <= array[middle] <= array[last]
// A side effect of this is that arrays of length <= 3 are sorted.
template<class T, class C>
static int find_pivot(T* array, int length, C comparator) {
assert(length > 1, "length of array must be > 0");
int middle_index = length / 2;
int last_index = length - 1;
if (comparator(array[0], array[middle_index]) == 1) {
swap(array, 0, middle_index);
}
if (comparator(array[0], array[last_index]) == 1) {
swap(array, 0, last_index);
}
if (comparator(array[middle_index], array[last_index]) == 1) {
swap(array, middle_index, last_index);
}
// Now the value in the middle of the array is the median
// of the fist, last and middle values. Use this as pivot.
return middle_index;
}
template<class T, class C, bool idempotent>
static int partition(T* array, int pivot, int length, C comparator) {
int left_index = -1;
int right_index = length;
T pivot_val = array[pivot];
while (true) {
do {
left_index++;
} while (comparator(array[left_index], pivot_val) == -1);
do {
right_index--;
} while (comparator(array[right_index], pivot_val) == 1);
if (left_index < right_index) {
if (!idempotent || comparator(array[left_index], array[right_index]) != 0) {
swap(array, left_index, right_index);
}
} else {
return right_index;
}
}
ShouldNotReachHere();
return 0;
}
template<class T, class C, bool idempotent>
static void inner_sort(T* array, int length, C comparator) {
if (length < 2) {
return;
}
int pivot = find_pivot(array, length, comparator);
if (length < 4) {
// arrays up to length 3 will be sorted after finding the pivot
return;
}
int split = partition<T, C, idempotent>(array, pivot, length, comparator);
int first_part_length = split + 1;
inner_sort<T, C, idempotent>(array, first_part_length, comparator);
inner_sort<T, C, idempotent>(&array[first_part_length], length - first_part_length, comparator);
}
public:
// The idempotent parameter prevents the sort from
// reordering a previous valid sort by not swapping
// fields that compare as equal. This requires extra
// calls to the comparator, so the performance
// impact depends on the comparator.
template<class T, class C>
static void sort(T* array, int length, C comparator, bool idempotent) {
// Switch "idempotent" from function paramter to template parameter
if (idempotent) {
inner_sort<T, C, true>(array, length, comparator);
} else {
inner_sort<T, C, false>(array, length, comparator);
}
}
// for unit testing
#ifndef PRODUCT
static void print_array(const char* prefix, int* array, int length);
static bool compare_arrays(int* actual, int* expected, int length);
template <class C> static bool sort_and_compare(int* arrayToSort, int* expectedResult, int length, C comparator, bool idempotent = false);
static void test_quick_sort();
#endif
};
#endif //SHARE_VM_UTILITIES_QUICKSORT_HPP
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