redis.clients.jedis.util.MurmurHash Maven / Gradle / Ivy

/*
 * 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 redis.clients.jedis.util;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based lookup. See
 * http://murmurhash.googlepages.com/ for more details. 

 * 
 * 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 implements Hashing {
  /**
   * Hashes bytes in an array.
   * @param data The bytes to hash.
   * @param seed The seed for the hash.
   * @return The 32 bit hash of the bytes in question.
   */
  public static int hash(byte[] data, int seed) {
    return hash(ByteBuffer.wrap(data), seed);
  }

  /**
   * Hashes bytes in part of an array.
   * @param data The data to hash.
   * @param offset Where to start munging.
   * @param length How many bytes to process.
   * @param seed The seed to start with.
   * @return The 32-bit hash of the data in question.
   */
  public static int hash(byte[] data, int offset, int length, int seed) {
    return hash(ByteBuffer.wrap(data, offset, length), seed);
  }

  /**
   * Hashes the bytes in a buffer from the current position to the limit.
   * @param buf The bytes to hash.
   * @param seed The seed for the hash.
   * @return The 32 bit murmur hash of the bytes in the buffer.
   */
  public static int hash(ByteBuffer buf, int seed) {
    // save byte order for later restoration
    ByteOrder byteOrder = buf.order();
    buf.order(ByteOrder.LITTLE_ENDIAN);

    int m = 0x5bd1e995;
    int r = 24;

    int h = seed ^ buf.remaining();

    int k;
    while (buf.remaining() >= 4) {
      k = buf.getInt();

      k *= m;
      k ^= k >>> r;
      k *= m;

      h *= m;
      h ^= k;
    }

    if (buf.remaining() > 0) {
      ByteBuffer finish = ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN);
      // for big-endian version, use this first:
      // finish.position(4-buf.remaining());
      finish.put(buf).rewind();
      h ^= finish.getInt();
      h *= m;
    }

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

    buf.order(byteOrder);
    return h;
  }

  public static long hash64A(byte[] data, int seed) {
    return hash64A(ByteBuffer.wrap(data), seed);
  }

  public static long hash64A(byte[] data, int offset, int length, int seed) {
    return hash64A(ByteBuffer.wrap(data, offset, length), seed);
  }

  public static long hash64A(ByteBuffer buf, int seed) {
    ByteOrder byteOrder = buf.order();
    buf.order(ByteOrder.LITTLE_ENDIAN);

    long m = 0xc6a4a7935bd1e995L;
    int r = 47;

    long h = seed ^ (buf.remaining() * m);

    long k;
    while (buf.remaining() >= 8) {
      k = buf.getLong();

      k *= m;
      k ^= k >>> r;
      k *= m;

      h ^= k;
      h *= m;
    }

    if (buf.remaining() > 0) {
      ByteBuffer finish = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN);
      // for big-endian version, do this first:
      // finish.position(8-buf.remaining());
      finish.put(buf).rewind();
      h ^= finish.getLong();
      h *= m;
    }

    h ^= h >>> r;
    h *= m;
    h ^= h >>> r;

    buf.order(byteOrder);
    return h;
  }

  @Override
  public long hash(byte[] key) {
    return hash64A(key, 0x1234ABCD);
  }

  @Override
  public long hash(String key) {
    return hash(SafeEncoder.encode(key));
  }
}