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3779
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1 /*
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2 * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24
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25 #ifndef SHARE_VM_UTILITIES_QUICKSORT_HPP
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26 #define SHARE_VM_UTILITIES_QUICKSORT_HPP
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27
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28 #include "memory/allocation.hpp"
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29 #include "runtime/globals.hpp"
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30 #include "utilities/debug.hpp"
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31
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32 class QuickSort : AllStatic {
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33
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34 private:
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35 template<class T>
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36 static void swap(T* array, int x, int y) {
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37 T tmp = array[x];
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38 array[x] = array[y];
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39 array[y] = tmp;
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40 }
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41
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42 // As pivot we use the median of the first, last and middle elements.
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43 // We swap in these three values at the right place in the array. This
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44 // means that this method not only returns the index of the pivot
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45 // element. It also alters the array so that:
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46 // array[first] <= array[middle] <= array[last]
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47 // A side effect of this is that arrays of length <= 3 are sorted.
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48 template<class T, class C>
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49 static int find_pivot(T* array, int length, C comparator) {
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50 assert(length > 1, "length of array must be > 0");
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51
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52 int middle_index = length / 2;
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53 int last_index = length - 1;
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54
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55 if (comparator(array[0], array[middle_index]) == 1) {
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56 swap(array, 0, middle_index);
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57 }
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58 if (comparator(array[0], array[last_index]) == 1) {
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59 swap(array, 0, last_index);
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60 }
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61 if (comparator(array[middle_index], array[last_index]) == 1) {
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62 swap(array, middle_index, last_index);
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63 }
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64 // Now the value in the middle of the array is the median
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65 // of the fist, last and middle values. Use this as pivot.
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66 return middle_index;
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67 }
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68
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69 template<class T, class C, bool idempotent>
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70 static int partition(T* array, int pivot, int length, C comparator) {
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71 int left_index = -1;
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72 int right_index = length;
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73 T pivot_val = array[pivot];
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74
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75 while (true) {
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76 do {
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77 left_index++;
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78 } while (comparator(array[left_index], pivot_val) == -1);
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79 do {
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80 right_index--;
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81 } while (comparator(array[right_index], pivot_val) == 1);
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82
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83 if (left_index < right_index) {
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84 if (!idempotent || comparator(array[left_index], array[right_index]) != 0) {
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85 swap(array, left_index, right_index);
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86 }
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87 } else {
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88 return right_index;
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89 }
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90 }
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91
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92 ShouldNotReachHere();
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93 return 0;
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94 }
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95
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96 template<class T, class C, bool idempotent>
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97 static void inner_sort(T* array, int length, C comparator) {
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98 if (length < 2) {
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99 return;
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100 }
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101 int pivot = find_pivot(array, length, comparator);
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102 if (length < 4) {
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103 // arrays up to length 3 will be sorted after finding the pivot
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104 return;
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105 }
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106 int split = partition<T, C, idempotent>(array, pivot, length, comparator);
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107 int first_part_length = split + 1;
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108 inner_sort<T, C, idempotent>(array, first_part_length, comparator);
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109 inner_sort<T, C, idempotent>(&array[first_part_length], length - first_part_length, comparator);
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110 }
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111
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112 public:
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113 // The idempotent parameter prevents the sort from
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114 // reordering a previous valid sort by not swapping
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115 // fields that compare as equal. This requires extra
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116 // calls to the comparator, so the performance
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117 // impact depends on the comparator.
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118 template<class T, class C>
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119 static void sort(T* array, int length, C comparator, bool idempotent) {
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120 // Switch "idempotent" from function paramter to template parameter
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121 if (idempotent) {
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122 inner_sort<T, C, true>(array, length, comparator);
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123 } else {
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124 inner_sort<T, C, false>(array, length, comparator);
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125 }
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126 }
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127
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128 // for unit testing
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129 #ifndef PRODUCT
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130 static void print_array(const char* prefix, int* array, int length);
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131 static bool compare_arrays(int* actual, int* expected, int length);
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132 template <class C> static bool sort_and_compare(int* arrayToSort, int* expectedResult, int length, C comparator, bool idempotent = false);
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4708
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133 static void test_quick_sort();
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3779
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134 #endif
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135 };
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136
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137
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138 #endif //SHARE_VM_UTILITIES_QUICKSORT_HPP
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