content: /*
   *
   * 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.
   *
   */
  package org.apache.bookkeeper.bookie.storage.ldb;
  
  import static com.google.common.base.Preconditions.checkArgument;
  
  import lombok.experimental.UtilityClass;
  
  /**
   * Sort an array of longs, grouping the items in tuples.
   *
   * <p>Group size decides how many longs are included in the tuples and key size controls how many items to use for
   * comparison.
   */
  @UtilityClass
  public class ArrayGroupSort {
  
      private static final int INSERTION_SORT_THRESHOLD = 100;
  
      private static final int GROUP_SIZE = 4;
  
      public void sort(long[] array) {
          sort(array, 0, array.length);
      }
  
      public static void sort(long[] array, int offset, int length) {
          checkArgument(length % GROUP_SIZE == 0, "Array length must be multiple of 4");
          quickSort(array, offset, (length + offset - GROUP_SIZE));
      }
  
      ////// Private
  
      private static void quickSort(long[] array, int low, int high) {
          if (low >= high) {
              return;
          }
  
          if (high - low < INSERTION_SORT_THRESHOLD) {
              insertionSort(array, low, high);
              return;
          }
  
          int pivotIdx = partition(array, low, high);
          quickSort(array, low, pivotIdx - GROUP_SIZE);
          quickSort(array, pivotIdx + GROUP_SIZE, high);
      }
  
      private static int alignGroup(int count) {
          return count - (count % GROUP_SIZE);
      }
  
      private static int partition(long[] array, int low, int high) {
          int mid = low + alignGroup((high - low) / 2);
          swap(array, mid, high);
  
          int i = low;
  
          for (int j = low; j < high; j += GROUP_SIZE) {
              if (isLess(array, j, high)) {
                  swap(array, j, i);
                  i += GROUP_SIZE;
              }
          }
  
          swap(array, i, high);
          return i;
      }
  
      private static void swap(long[] array, int a, int b) {
          long tmp0 = array[a];
          long tmp1 = array[a + 1];
          long tmp2 = array[a + 2];
          long tmp3 = array[a + 3];
  
          array[a] = array[b];
          array[a + 1] = array[b + 1];
          array[a + 2] = array[b + 2];
          array[a + 3] = array[b + 3];
  
          array[b] = tmp0;
          array[b + 1] = tmp1;
          array[b + 2] = tmp2;
          array[b + 3] = tmp3;
      }
  
      private static boolean isLess(long[] array, int a, int b) {
          long a0 = array[a];
          long b0 = array[b];
  
          if (a0 < b0) {
              return true;
          } else if (a0 > b0) {
              return false;
          }
  
          return array[a + 1] < array[b + 1];
      }
  
      private static void insertionSort(long[] a, int low, int high) {
          for (int i = low + GROUP_SIZE; i <= high; i += GROUP_SIZE) {
              int j = i;
              while (j > 0 && isLess(a, j, j - GROUP_SIZE)) {
                  swap(a, j, j - GROUP_SIZE);
                  j -= GROUP_SIZE;
              }
          }
      }
  }
  