com.google.common.hash.Murmur3_128HashFunction Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of guava Show documentation
Builds the guava lib. Requires the jsr305 be built first.
There is a newer version: 33.3.0-jre-r3
/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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.
 */

/*
 * MurmurHash3 was written by Austin Appleby, and is placed in the public
 * domain. The author hereby disclaims copyright to this source code.
 */

/*
 * Source:
 * https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp
 * (Modified to adapt to Guava coding conventions and to use the HashFunction interface)
 */

package com.google.common.hash;

import static com.google.common.primitives.UnsignedBytes.toInt;

import com.google.errorprone.annotations.Immutable;
import java.io.Serializable;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import javax.annotation.CheckForNull;

/**
 * See MurmurHash3_x64_128 in the
 * C++ implementation.
 *
 * @author Austin Appleby
 * @author Dimitris Andreou
 */
@Immutable
@ElementTypesAreNonnullByDefault
final class Murmur3_128HashFunction extends AbstractHashFunction implements Serializable {
  static final HashFunction MURMUR3_128 = new Murmur3_128HashFunction(0);

  static final HashFunction GOOD_FAST_HASH_128 =
      new Murmur3_128HashFunction(Hashing.GOOD_FAST_HASH_SEED);

  // TODO(user): when the shortcuts are implemented, update BloomFilterStrategies
  private final int seed;

  Murmur3_128HashFunction(int seed) {
    this.seed = seed;
  }

  @Override
  public int bits() {
    return 128;
  }

  @Override
  public Hasher newHasher() {
    return new Murmur3_128Hasher(seed);
  }

  @Override
  public String toString() {
    return "Hashing.murmur3_128(" + seed + ")";
  }

  @Override
  public boolean equals(@CheckForNull Object object) {
    if (object instanceof Murmur3_128HashFunction) {
      Murmur3_128HashFunction other = (Murmur3_128HashFunction) object;
      return seed == other.seed;
    }
    return false;
  }

  @Override
  public int hashCode() {
    return getClass().hashCode() ^ seed;
  }

  private static final class Murmur3_128Hasher extends AbstractStreamingHasher {
    private static final int CHUNK_SIZE = 16;
    private static final long C1 = 0x87c37b91114253d5L;
    private static final long C2 = 0x4cf5ad432745937fL;
    private long h1;
    private long h2;
    private int length;

    Murmur3_128Hasher(int seed) {
      super(CHUNK_SIZE);
      this.h1 = seed;
      this.h2 = seed;
      this.length = 0;
    }

    @Override
    protected void process(ByteBuffer bb) {
      long k1 = bb.getLong();
      long k2 = bb.getLong();
      bmix64(k1, k2);
      length += CHUNK_SIZE;
    }

    private void bmix64(long k1, long k2) {
      h1 ^= mixK1(k1);

      h1 = Long.rotateLeft(h1, 27);
      h1 += h2;
      h1 = h1 * 5 + 0x52dce729;

      h2 ^= mixK2(k2);

      h2 = Long.rotateLeft(h2, 31);
      h2 += h1;
      h2 = h2 * 5 + 0x38495ab5;
    }

    @Override
    protected void processRemaining(ByteBuffer bb) {
      long k1 = 0;
      long k2 = 0;
      length += bb.remaining();
      switch (bb.remaining()) {
        case 15:
          k2 ^= (long) toInt(bb.get(14)) << 48; // fall through
        case 14:
          k2 ^= (long) toInt(bb.get(13)) << 40; // fall through
        case 13:
          k2 ^= (long) toInt(bb.get(12)) << 32; // fall through
        case 12:
          k2 ^= (long) toInt(bb.get(11)) << 24; // fall through
        case 11:
          k2 ^= (long) toInt(bb.get(10)) << 16; // fall through
        case 10:
          k2 ^= (long) toInt(bb.get(9)) << 8; // fall through
        case 9:
          k2 ^= (long) toInt(bb.get(8)); // fall through
        case 8:
          k1 ^= bb.getLong();
          break;
        case 7:
          k1 ^= (long) toInt(bb.get(6)) << 48; // fall through
        case 6:
          k1 ^= (long) toInt(bb.get(5)) << 40; // fall through
        case 5:
          k1 ^= (long) toInt(bb.get(4)) << 32; // fall through
        case 4:
          k1 ^= (long) toInt(bb.get(3)) << 24; // fall through
        case 3:
          k1 ^= (long) toInt(bb.get(2)) << 16; // fall through
        case 2:
          k1 ^= (long) toInt(bb.get(1)) << 8; // fall through
        case 1:
          k1 ^= (long) toInt(bb.get(0));
          break;
        default:
          throw new AssertionError("Should never get here.");
      }
      h1 ^= mixK1(k1);
      h2 ^= mixK2(k2);
    }

    @Override
    protected HashCode makeHash() {
      h1 ^= length;
      h2 ^= length;

      h1 += h2;
      h2 += h1;

      h1 = fmix64(h1);
      h2 = fmix64(h2);

      h1 += h2;
      h2 += h1;

      return HashCode.fromBytesNoCopy(
          ByteBuffer.wrap(new byte[CHUNK_SIZE])
              .order(ByteOrder.LITTLE_ENDIAN)
              .putLong(h1)
              .putLong(h2)
              .array());
    }

    private static long fmix64(long k) {
      k ^= k >>> 33;
      k *= 0xff51afd7ed558ccdL;
      k ^= k >>> 33;
      k *= 0xc4ceb9fe1a85ec53L;
      k ^= k >>> 33;
      return k;
    }

    private static long mixK1(long k1) {
      k1 *= C1;
      k1 = Long.rotateLeft(k1, 31);
      k1 *= C2;
      return k1;
    }

    private static long mixK2(long k2) {
      k2 *= C2;
      k2 = Long.rotateLeft(k2, 33);
      k2 *= C1;
      return k2;
    }
  }

  private static final long serialVersionUID = 0L;
}