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/*
 * 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.hudi.common.util.hash;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup.  See http://murmurhash.googlepages.com/ for more details.
 * 
 * The code in class is ported from {@link org.apache.hadoop.util.hash.MurmurHash} in Apache Hadoop.
 * 

 * 
The C version of MurmurHash 2.0 found at that site was ported
 * to Java by Andrzej Bialecki (ab at getopt org).
 */
public class MurmurHash extends Hash {
  private static MurmurHash _instance = new MurmurHash();

  public static Hash getInstance() {
    return _instance;
  }

  @Override
  public int hash(byte[] data, int length, int seed) {
    return hash(data, 0, length, seed);
  }

  public int hash(byte[] data, int offset, int length, int seed) {
    int m = 0x5bd1e995;
    int r = 24;

    int h = seed ^ length;

    int len4 = length >> 2;

    for (int i = 0; i < len4; i++) {
      int i4 = offset + (i << 2);
      int k = data[i4 + 3];
      k = k << 8;
      k = k | (data[i4 + 2] & 0xff);
      k = k << 8;
      k = k | (data[i4 + 1] & 0xff);
      k = k << 8;
      k = k | (data[i4 + 0] & 0xff);
      k *= m;
      k ^= k >>> r;
      k *= m;
      h *= m;
      h ^= k;
    }

    // avoid calculating modulo
    int lenM = len4 << 2;
    int left = length - lenM;

    if (left != 0) {
      length += offset;
      if (left >= 3) {
        h ^= (int) data[length - 3] << 16;
      }
      if (left >= 2) {
        h ^= (int) data[length - 2] << 8;
      }
      if (left >= 1) {
        h ^= (int) data[length - 1];
      }

      h *= m;
    }

    h ^= h >>> 13;
    h *= m;
    h ^= h >>> 15;

    return h;
  }
}