aoqi@0: /*
aoqi@0:  * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
aoqi@0:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
aoqi@0:  *
aoqi@0:  * This code is free software; you can redistribute it and/or modify it
aoqi@0:  * under the terms of the GNU General Public License version 2 only, as
aoqi@0:  * published by the Free Software Foundation.
aoqi@0:  *
aoqi@0:  * This code is distributed in the hope that it will be useful, but WITHOUT
aoqi@0:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
aoqi@0:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
aoqi@0:  * version 2 for more details (a copy is included in the LICENSE file that
aoqi@0:  * accompanied this code).
aoqi@0:  *
aoqi@0:  * You should have received a copy of the GNU General Public License version
aoqi@0:  * 2 along with this work; if not, write to the Free Software Foundation,
aoqi@0:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
aoqi@0:  *
aoqi@0:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
aoqi@0:  * or visit www.oracle.com if you need additional information or have any
aoqi@0:  * questions.
aoqi@0:  *
aoqi@0:  */
aoqi@0: 
aoqi@0: #ifndef SHARE_VM_UTILITIES_QUICKSORT_HPP
aoqi@0: #define SHARE_VM_UTILITIES_QUICKSORT_HPP
aoqi@0: 
aoqi@0: #include "memory/allocation.hpp"
aoqi@0: #include "runtime/globals.hpp"
aoqi@0: #include "utilities/debug.hpp"
aoqi@0: 
aoqi@0: class QuickSort : AllStatic {
aoqi@0: 
aoqi@0:  private:
aoqi@0:   template<class T>
aoqi@0:   static void swap(T* array, int x, int y) {
aoqi@0:     T tmp = array[x];
aoqi@0:     array[x] = array[y];
aoqi@0:     array[y] = tmp;
aoqi@0:   }
aoqi@0: 
aoqi@0:   // As pivot we use the median of the first, last and middle elements.
aoqi@0:   // We swap in these three values at the right place in the array. This
aoqi@0:   // means that this method not only returns the index of the pivot
aoqi@0:   // element. It also alters the array so that:
aoqi@0:   //     array[first] <= array[middle] <= array[last]
aoqi@0:   // A side effect of this is that arrays of length <= 3 are sorted.
aoqi@0:   template<class T, class C>
aoqi@0:   static int find_pivot(T* array, int length, C comparator) {
aoqi@0:     assert(length > 1, "length of array must be > 0");
aoqi@0: 
aoqi@0:     int middle_index = length / 2;
aoqi@0:     int last_index = length - 1;
aoqi@0: 
aoqi@0:     if (comparator(array[0], array[middle_index]) == 1) {
aoqi@0:       swap(array, 0, middle_index);
aoqi@0:     }
aoqi@0:     if (comparator(array[0], array[last_index]) == 1) {
aoqi@0:       swap(array, 0, last_index);
aoqi@0:     }
aoqi@0:     if (comparator(array[middle_index], array[last_index]) == 1) {
aoqi@0:       swap(array, middle_index, last_index);
aoqi@0:     }
aoqi@0:     // Now the value in the middle of the array is the median
aoqi@0:     // of the fist, last and middle values. Use this as pivot.
aoqi@0:     return middle_index;
aoqi@0:   }
aoqi@0: 
aoqi@0:   template<class T, class C, bool idempotent>
aoqi@0:   static int partition(T* array, int pivot, int length, C comparator) {
aoqi@0:     int left_index = -1;
aoqi@0:     int right_index = length;
aoqi@0:     T pivot_val = array[pivot];
aoqi@0: 
aoqi@0:     while (true) {
aoqi@0:       do {
aoqi@0:         left_index++;
aoqi@0:       } while (comparator(array[left_index], pivot_val) == -1);
aoqi@0:       do {
aoqi@0:         right_index--;
aoqi@0:       } while (comparator(array[right_index], pivot_val) == 1);
aoqi@0: 
aoqi@0:       if (left_index < right_index) {
aoqi@0:         if (!idempotent || comparator(array[left_index], array[right_index]) != 0) {
aoqi@0:           swap(array, left_index, right_index);
aoqi@0:         }
aoqi@0:       } else {
aoqi@0:         return right_index;
aoqi@0:       }
aoqi@0:     }
aoqi@0: 
aoqi@0:     ShouldNotReachHere();
aoqi@0:     return 0;
aoqi@0:   }
aoqi@0: 
aoqi@0:   template<class T, class C, bool idempotent>
aoqi@0:   static void inner_sort(T* array, int length, C comparator) {
aoqi@0:     if (length < 2) {
aoqi@0:       return;
aoqi@0:     }
aoqi@0:     int pivot = find_pivot(array, length, comparator);
aoqi@0:     if (length < 4) {
aoqi@0:       // arrays up to length 3 will be sorted after finding the pivot
aoqi@0:       return;
aoqi@0:     }
aoqi@0:     int split = partition<T, C, idempotent>(array, pivot, length, comparator);
aoqi@0:     int first_part_length = split + 1;
aoqi@0:     inner_sort<T, C, idempotent>(array, first_part_length, comparator);
aoqi@0:     inner_sort<T, C, idempotent>(&array[first_part_length], length - first_part_length, comparator);
aoqi@0:   }
aoqi@0: 
aoqi@0:  public:
aoqi@0:   // The idempotent parameter prevents the sort from
aoqi@0:   // reordering a previous valid sort by not swapping
aoqi@0:   // fields that compare as equal. This requires extra
aoqi@0:   // calls to the comparator, so the performance
aoqi@0:   // impact depends on the comparator.
aoqi@0:   template<class T, class C>
aoqi@0:   static void sort(T* array, int length, C comparator, bool idempotent) {
aoqi@0:     // Switch "idempotent" from function paramter to template parameter
aoqi@0:     if (idempotent) {
aoqi@0:       inner_sort<T, C, true>(array, length, comparator);
aoqi@0:     } else {
aoqi@0:       inner_sort<T, C, false>(array, length, comparator);
aoqi@0:     }
aoqi@0:   }
aoqi@0: 
aoqi@0:   // for unit testing
aoqi@0: #ifndef PRODUCT
aoqi@0:   static void print_array(const char* prefix, int* array, int length);
aoqi@0:   static bool compare_arrays(int* actual, int* expected, int length);
aoqi@0:   template <class C> static bool sort_and_compare(int* arrayToSort, int* expectedResult, int length, C comparator, bool idempotent = false);
aoqi@0:   static void test_quick_sort();
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: 
aoqi@0: #endif //SHARE_VM_UTILITIES_QUICKSORT_HPP