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

/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2016 DiffPlug.
 *
 * 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.
 */
package com.diffplug.common.hash;

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

import java.io.Serializable;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

import javax.annotation.Nullable;

/**
 * See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
 * MurmurHash3_x64_128
 *
 * @author Austin Appleby
 * @author Dimitris Andreou
 */
final class Murmur3_128HashFunction extends AbstractStreamingHashFunction implements Serializable {
	// 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(@Nullable 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
		public 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;
}