content: 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.
   */
  
  /**
   * This class was inspired by CGLIB, but provides a better
   * QuickSort algorithm without additional InsertionSort
   * at the end.
   * To use, subclass and override the four abstract methods
   * which compare and modify your data.
   * Allows custom swap so that two arrays can be sorted
   * at the same time.
   * @lucene.internal
   */
  public abstract class SorterTemplate {
  
    private static final int MERGESORT_THRESHOLD = 12;
    private static final int QUICKSORT_THRESHOLD = 7;
  
    /** Implement this method, that swaps slots {@code i} and {@code j} in your data */
    protected abstract void swap(int i, int j);
    
    /** Compares slots {@code i} and {@code j} of you data.
     * Should be implemented like <code><em>valueOf(i)</em>.compareTo(<em>valueOf(j)</em>)</code> */
    protected abstract int compare(int i, int j);
  
    /** Implement this method, that stores the value of slot {@code i} as pivot value */
    protected abstract void setPivot(int i);
    
    /** Implements the compare function for the previously stored pivot value.
     * Should be implemented like <code>pivot.compareTo(<em>valueOf(j)</em>)</code> */
    protected abstract int comparePivot(int j);
    
    /** Sorts via stable in-place InsertionSort algorithm
     *(ideal for small collections which are mostly presorted). */
    public final void insertionSort(int lo, int hi) {
      for (int i = lo + 1 ; i <= hi; i++) {
        for (int j = i; j > lo; j--) {
          if (compare(j - 1, j) > 0) {
            swap(j - 1, j);
          } else {
            break;
          }
        }
      }
    }
  
    /** Sorts via in-place, but unstable, QuickSort algorithm.
     * For small collections falls back to {@link #insertionSort(int,int)}. */
    public final void quickSort(final int lo, final int hi) {
      if (hi <= lo) return;
      // from Integer's Javadocs: ceil(log2(x)) = 32 - numberOfLeadingZeros(x - 1)
      quickSort(lo, hi, (Integer.SIZE - Integer.numberOfLeadingZeros(hi - lo)) << 1);
    }
    
    private void quickSort(int lo, int hi, int maxDepth) {
      // fall back to insertion when array has short length
      final int diff = hi - lo;
      if (diff <= QUICKSORT_THRESHOLD) {
        insertionSort(lo, hi);
        return;
      }
      
      // fall back to merge sort when recursion depth gets too big
      if (--maxDepth == 0) {
        mergeSort(lo, hi);
        return;
      }
      
      final int mid = lo + (diff >>> 1);
      
      if (compare(lo, mid) > 0) {
        swap(lo, mid);
      }
  
      if (compare(mid, hi) > 0) {
        swap(mid, hi);
        if (compare(lo, mid) > 0) {
          swap(lo, mid);
        }
      }
      
      int left = lo + 1;
      int right = hi - 1;
  
      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(lo, left, maxDepth);
      quickSort(left + 1, hi, maxDepth);
    }
    
    /** Sorts via stable in-place MergeSort algorithm
     * For small collections falls back to {@link #insertionSort(int,int)}. */
    public final void mergeSort(int lo, int hi) {
      final int diff = hi - lo;
      if (diff <= MERGESORT_THRESHOLD) {
        insertionSort(lo, hi);
        return;
      }
      
      final int mid = lo + (diff >>> 1);
      
      mergeSort(lo, mid);
      mergeSort(mid, hi);
      merge(lo, mid, hi, mid - lo, hi - mid);
    }
  
    private void merge(int lo, int pivot, int hi, int len1, int len2) {
      if (len1 == 0 || len2 == 0) {
        return;
      }
      if (len1 + len2 == 2) {
        if (compare(pivot, lo) < 0) {
            swap(pivot, lo);
        }
        return;
      }
      int first_cut, second_cut;
      int len11, len22;
      if (len1 > len2) {
        len11 = len1 >>> 1;
        first_cut = lo + len11;
        second_cut = lower(pivot, hi, first_cut);
        len22 = second_cut - pivot;
      } else {
        len22 = len2 >>> 1;
        second_cut = pivot + len22;
        first_cut = upper(lo, pivot, second_cut);
        len11 = first_cut - lo;
      }
      rotate(first_cut, pivot, second_cut);
      final int new_mid = first_cut + len22;
      merge(lo, first_cut, new_mid, len11, len22);
      merge(new_mid, second_cut, hi, len1 - len11, len2 - len22);
    }
  
    private void rotate(int lo, int mid, int hi) {
      int lot = lo;
      int hit = mid - 1;
      while (lot < hit) {
        swap(lot++, hit--);
      }
      lot = mid; hit = hi - 1;
      while (lot < hit) {
        swap(lot++, hit--);
      }
      lot = lo; hit = hi - 1;
      while (lot < hit) {
        swap(lot++, hit--);
      }
    }
  
    private int lower(int lo, int hi, int val) {
      int len = hi - lo;
      while (len > 0) {
        final int half = len >>> 1,
          mid = lo + half;
        if (compare(mid, val) < 0) {
          lo = mid + 1;
          len = len - half -1;
        } else {
          len = half;
        }
      }
      return lo;
    }
  
    private int upper(int lo, int hi, int val) {
      int len = hi - lo;
      while (len > 0) {
        final int half = len >>> 1,
          mid = lo + half;
        if (compare(val, mid) < 0) {
          len = half;
        } else {
          lo = mid + 1;
          len = len - half -1;
        }
      }
      return lo;
    }
  
  }
  