| package org.apache.lucene.util; |
| |
| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| /** |
| * {@link Sorter} implementation based on a variant of the quicksort algorithm |
| * called <a href="http://en.wikipedia.org/wiki/Introsort">introsort</a>: when |
| * the recursion level exceeds the log of the length of the array to sort, it |
| * falls back to heapsort. This prevents quicksort from running into its |
| * worst-case quadratic runtime. Small arrays are sorted with |
| * insertion sort. |
| * @lucene.internal |
| */ |
| public abstract class IntroSorter extends Sorter { |
| |
| static int ceilLog2(int n) { |
| return Integer.SIZE - Integer.numberOfLeadingZeros(n - 1); |
| } |
| |
| /** Create a new {@link IntroSorter}. */ |
| public IntroSorter() {} |
| |
| @Override |
| public final void sort(int from, int to) { |
| checkRange(from, to); |
| quicksort(from, to, ceilLog2(to - from)); |
| } |
| |
| void quicksort(int from, int to, int maxDepth) { |
| if (to - from < THRESHOLD) { |
| insertionSort(from, to); |
| return; |
| } else if (--maxDepth < 0) { |
| heapSort(from, to); |
| return; |
| } |
| |
| final int mid = (from + to) >>> 1; |
| |
| if (compare(from, mid) > 0) { |
| swap(from, mid); |
| } |
| |
| if (compare(mid, to - 1) > 0) { |
| swap(mid, to - 1); |
| if (compare(from, mid) > 0) { |
| swap(from, mid); |
| } |
| } |
| |
| int left = from + 1; |
| int right = to - 2; |
| |
| setPivot(mid); |
| for (;;) { |
| while (comparePivot(right) < 0) { |
| --right; |
| } |
| |
| while (left < right && comparePivot(left) >= 0) { |
| ++left; |
| } |
| |
| if (left < right) { |
| swap(left, right); |
| --right; |
| } else { |
| break; |
| } |
| } |
| |
| quicksort(from, left + 1, maxDepth); |
| quicksort(left + 1, to, maxDepth); |
| } |
| |
| /** Save the value at slot <code>i</code> so that it can later be used as a |
| * pivot, see {@link #comparePivot(int)}. */ |
| protected abstract void setPivot(int i); |
| |
| /** Compare the pivot with the slot at <code>j</code>, similarly to |
| * {@link #compare(int, int) compare(i, j)}. */ |
| protected abstract int comparePivot(int j); |
| } |