/*

  * 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.mapping;

 import org.apache.hadoop.io.LongWritable;

 /**

  * MappingStoreOps implementation used to embed target information into

  * vertex id. Stores information in the higher order bits of the long id

  */

 public class DefaultEmbeddedLongByteOps extends AbstractLongByteOps {

   /** Bit mask for first 9 bits in a long */

   private static final long MASK = ((long) 0x1FF) << 55;

   /** Inverse of MASK */

   private static final long IMASK = ~ MASK;

   /**

    * Default constructor (do not use)

    */

   public DefaultEmbeddedLongByteOps() {

   }

   @Override

   public boolean hasEmbedding() {

     return true;

   }

   @Override

   public void embedTargetInfo(LongWritable id) {

     if ((id.get() & MASK) != 0) {

       throw new IllegalStateException("Expected first 9 bits of long " +

           " to be empty");

     }

     byte target = mappingStore.getByteTarget(id);

     // first bit = 0 & rest 8 bits set to target

     // add 1 to distinguish between not set and assignment to worker-0

     // (prefix bits = 0 can mean one of two things :

     // no entry in the mapping, in which case target = -1, so -1 + 1 = 0

     // vertex is created later during computation, so prefix bits are 0 anyway)

     long maskValue = ((1L + target) & 0xFF) << 55;

     id.set(id.get() | maskValue);

   }

   @Override

   public void removeTargetInfo(LongWritable id) {

     id.set(id.get() & IMASK);

   }

   @Override

   public int getPartition(LongWritable id, int partitionCount,

     int workerCount) {

     // extract last 8 bits

     // subtract 1 since added 1 during embedInfo (unset = -1)

     byte target = (byte) (((id.get() >>> 55) & 0xFF) - 1);

     return computePartition(id, partitionCount, workerCount, target);

   }

 }