/*

  * 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.giraph.partition;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 import com.google.common.primitives.UnsignedInts;

 /**

  * Divides the vertices into partitions by their hash code using ranges of the

  * hash space.

  *

  * @param <I> Vertex index value

  * @param <V> Vertex value

  * @param <E> Edge value

  */

 @SuppressWarnings("rawtypes")

 public class HashRangePartitionerFactory<I extends WritableComparable,

     V extends Writable, E extends Writable>

     extends GraphPartitionerFactory<I, V, E> {

   /** A transformed hashCode() must be strictly smaller than this. */

   private static final long HASH_LIMIT = 2L * Integer.MAX_VALUE + 2L;

   @Override

   public int getPartition(I id, int partitionCount, int workerCount) {

     long unsignedHashCode = UnsignedInts.toLong(id.hashCode());

     // The reader can verify that unsignedHashCode of HASH_LIMIT - 1 yields

     // index of size - 1, and unsignedHashCode of 0 yields index of 0.

     return (int) ((unsignedHashCode * partitionCount) / HASH_LIMIT);

   }

   @Override

   public int getWorker(int partition, int partitionCount, int workerCount) {

     return partition % workerCount;

   }

 }