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org.mozilla.javascript.Sorting Maven / Gradle / Ivy
Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically
embedded into Java applications to provide scripting to end users.
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
package org.mozilla.javascript;
import java.util.Comparator;
public final class Sorting {
private static final int SMALLSORT = 16;
private static final Sorting sorting = new Sorting();
private Sorting() {}
public static Sorting get() {
return sorting;
}
public void insertionSort(Object[] a, Comparator cmp) {
insertionSort(a, 0, a.length - 1, cmp);
}
private static void insertionSort(Object[] a, int start, int end, Comparator cmp) {
int i = start;
while (i <= end) {
Object x = a[i];
int j = i - 1;
while ((j >= start) && (cmp.compare(a[j], x) > 0)) {
a[j + 1] = a[j];
j--;
}
a[j + 1] = x;
i++;
}
}
/*
Hybrid sorting mechanism similar to Introsort by David Musser. Uses quicksort's
partitioning mechanism recursively until the resulting array is small or the
recursion is too deep, and then use insertion sort for the rest.
This is the same basic algorithm used by the GNU Standard C++ library.
*/
public void hybridSort(Object[] a, Comparator cmp) {
hybridSort(a, 0, a.length - 1, cmp, log2(a.length) * 2);
}
private void hybridSort(Object[] a, int start, int end, Comparator cmp, int maxdepth) {
if (start < end) {
if ((maxdepth == 0) || ((end - start) <= SMALLSORT)) {
insertionSort(a, start, end, cmp);
} else {
int p = partition(a, start, end, cmp);
hybridSort(a, start, p, cmp, maxdepth - 1);
hybridSort(a, p + 1, end, cmp, maxdepth - 1);
}
}
}
/*
Quicksort-style partitioning, using the Hoare partition scheme as coded by
Sedgewick at https://algs4.cs.princeton.edu/23quicksort/Quick.java.html.
Use the "median of three" method to determine which index to pivot on, and then
separate the array into two halves based on the pivot.
*/
private int partition(Object[] a, int start, int end, Comparator cmp) {
final int p = median(a, start, end, cmp);
final Object pivot = a[p];
a[p] = a[start];
a[start] = pivot;
int i = start;
int j = end + 1;
while (true) {
while (cmp.compare(a[++i], pivot) < 0) {
if (i == end) {
break;
}
}
while (cmp.compare(a[--j], pivot) >= 0) {
if (j == start) {
break;
}
}
if (i >= j) {
break;
}
swap(a, i, j);
}
swap(a, start, j);
return j;
}
private static void swap(Object[] a, int l, int h) {
final Object tmp = a[l];
a[l] = a[h];
a[h] = tmp;
}
private static int log2(int n) {
return (int) (Math.log10(n) / Math.log10(2.0));
}
/*
Return the index of the median of three elements in the specified array range -- the
first, the last, and the one in the middle.
*/
public int median(final Object[] a, int start, int end, Comparator cmp) {
final int m = start + ((end - start) / 2);
int smallest = start;
if (cmp.compare(a[smallest], a[m]) > 0) {
smallest = m;
}
if (cmp.compare(a[smallest], a[end]) > 0) {
smallest = end;
}
if (smallest == start) {
return (cmp.compare(a[m], a[end]) < 0) ? m : end;
}
if (smallest == m) {
return (cmp.compare(a[start], a[end]) < 0) ? start : end;
}
return (cmp.compare(a[start], a[m]) < 0) ? start : m;
}
}
