lib/java/src/org/apache/thrift/IntRangeSet.java

/*
 * 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.thrift;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

/**
 * IntRangeSet is a specialized Set<Integer> implementation designed 
 * specifically to make the generated validate() method calls faster. It groups
 * the set values into ranges, and in the contains() call, it does 
 * num ranges * 2 comparisons max. For the common case, which is a single, 
 * contiguous range, this approach is about 60% faster than using a HashSet. If
 * you had a very ragged value set, like all the odd numbers, for instance, 
 * then you would end up with pretty poor running time.  
 */
public class IntRangeSet implements Set<Integer> {
  /**
   * This array keeps the bounds of each extent in alternating cells, always 
   * increasing. Example: [0,5,10,15], which corresponds to 0-5, 10-15.
   */
  private int[] extents;
  
  /**
   * We'll keep a duplicate, real HashSet around internally to satisfy some of
   * the other set operations. 
   */
  private Set<Integer> realSet = new HashSet<Integer>();
  
  public IntRangeSet(int... values) {
    Arrays.sort(values);

    List<Integer> extent_list = new ArrayList<Integer>();
    
    int ext_start = values[0];
    int ext_end_so_far = values[0];
    for (int i = 1; i < values.length; i++) {
      realSet.add(values[i]);
      
      if (values[i] == ext_end_so_far + 1) {
        // advance the end so far
        ext_end_so_far = values[i];
      } else {
        // create an extent for everything we saw so far, move on to the next one
        extent_list.add(ext_start);
        extent_list.add(ext_end_so_far);
        ext_start = values[i];
        ext_end_so_far = values[i];
      }
    }
    extent_list.add(ext_start);
    extent_list.add(ext_end_so_far);
    
    extents = new int[extent_list.size()];
    for (int i = 0; i < extent_list.size(); i++) {
      extents[i] = extent_list.get(i);
    }
  }
  
  public boolean add(Integer i) {
    throw new UnsupportedOperationException();
  }
  
  public void clear() {
    throw new UnsupportedOperationException();
  }

  public boolean addAll(Collection<? extends Integer> arg0) {
    throw new UnsupportedOperationException();
  }

  /**
   * While this method is here for Set interface compatibility, you should avoid 
   * using it. It incurs boxing overhead! Use the int method directly, instead.
   */
  public boolean contains(Object arg0) {
    return contains(((Integer)arg0).intValue());
  }

  /**
   * This is much faster, since it doesn't stop at Integer on the way through.
   * @param val the value you want to check set membership for
   * @return true if val was found, false otherwise
   */
  public boolean contains(int val) {
    for (int i = 0; i < extents.length / 2; i++) {
      if (val < extents[i*2]) {
        return false;
      } else if (val <= extents[i*2+1]) {
        return true;
      }
    }
    
    return false;
  }
  
  public boolean containsAll(Collection<?> arg0) {
    for (Object o : arg0) {
      if (!contains(o)) {
        return false;
      }
    }
    return true;
  }

  public boolean isEmpty() {
    return realSet.isEmpty();
  }

  public Iterator<Integer> iterator() {
    return realSet.iterator();
  }

  public boolean remove(Object arg0) {
    throw new UnsupportedOperationException();
  }

  public boolean removeAll(Collection<?> arg0) {
    throw new UnsupportedOperationException();
  }

  public boolean retainAll(Collection<?> arg0) {
    throw new UnsupportedOperationException();
  }

  public int size() {
    return realSet.size();
  }

  public Object[] toArray() {
    return realSet.toArray();
  }

  public <T> T[] toArray(T[] arg0) {
    return realSet.toArray(arg0);
  }
  
  @Override
  public String toString() {
    String buf = "";
    for (int i = 0; i < extents.length / 2; i++) {
      if (i != 0) { 
        buf += ", ";
      }
      buf += "[" + extents[i*2] + "," + extents[i*2+1] + "]"; 
    }
    return buf;
  }
}