com.diffplug.common.hash.Murmur3_32HashFunction 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 javax.annotation.Nullable;

import com.diffplug.common.primitives.Chars;
import com.diffplug.common.primitives.Ints;
import com.diffplug.common.primitives.Longs;

/**
 * See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
 * MurmurHash3_x86_32
 *
 * @author Austin Appleby
 * @author Dimitris Andreou
 * @author Kurt Alfred Kluever
 */
final class Murmur3_32HashFunction extends AbstractStreamingHashFunction implements Serializable {
	private static final int C1 = 0xcc9e2d51;
	private static final int C2 = 0x1b873593;

	private final int seed;

	Murmur3_32HashFunction(int seed) {
		this.seed = seed;
	}

	@Override
	public int bits() {
		return 32;
	}

	@Override
	public Hasher newHasher() {
		return new Murmur3_32Hasher(seed);
	}

	@Override
	public String toString() {
		return "Hashing.murmur3_32(" + seed + ")";
	}

	@Override
	public boolean equals(@Nullable Object object) {
		if (object instanceof Murmur3_32HashFunction) {
			Murmur3_32HashFunction other = (Murmur3_32HashFunction) object;
			return seed == other.seed;
		}
		return false;
	}

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

	@Override
	public HashCode hashInt(int input) {
		int k1 = mixK1(input);
		int h1 = mixH1(seed, k1);

		return fmix(h1, Ints.BYTES);
	}

	@Override
	public HashCode hashLong(long input) {
		int low = (int) input;
		int high = (int) (input >>> 32);

		int k1 = mixK1(low);
		int h1 = mixH1(seed, k1);

		k1 = mixK1(high);
		h1 = mixH1(h1, k1);

		return fmix(h1, Longs.BYTES);
	}

	// TODO(kak): Maybe implement #hashBytes instead?
	@Override
	public HashCode hashUnencodedChars(CharSequence input) {
		int h1 = seed;

		// step through the CharSequence 2 chars at a time
		for (int i = 1; i < input.length(); i += 2) {
			int k1 = input.charAt(i - 1) | (input.charAt(i) << 16);
			k1 = mixK1(k1);
			h1 = mixH1(h1, k1);
		}

		// deal with any remaining characters
		if ((input.length() & 1) == 1) {
			int k1 = input.charAt(input.length() - 1);
			k1 = mixK1(k1);
			h1 ^= k1;
		}

		return fmix(h1, Chars.BYTES * input.length());
	}

	private static int mixK1(int k1) {
		k1 *= C1;
		k1 = Integer.rotateLeft(k1, 15);
		k1 *= C2;
		return k1;
	}

	private static int mixH1(int h1, int k1) {
		h1 ^= k1;
		h1 = Integer.rotateLeft(h1, 13);
		h1 = h1 * 5 + 0xe6546b64;
		return h1;
	}

	// Finalization mix - force all bits of a hash block to avalanche
	private static HashCode fmix(int h1, int length) {
		h1 ^= length;
		h1 ^= h1 >>> 16;
		h1 *= 0x85ebca6b;
		h1 ^= h1 >>> 13;
		h1 *= 0xc2b2ae35;
		h1 ^= h1 >>> 16;
		return HashCode.fromInt(h1);
	}

	private static final class Murmur3_32Hasher extends AbstractStreamingHasher {
		private static final int CHUNK_SIZE = 4;
		private int h1;
		private int length;

		Murmur3_32Hasher(int seed) {
			super(CHUNK_SIZE);
			this.h1 = seed;
			this.length = 0;
		}

		@Override
		protected void process(ByteBuffer bb) {
			int k1 = Murmur3_32HashFunction.mixK1(bb.getInt());
			h1 = Murmur3_32HashFunction.mixH1(h1, k1);
			length += CHUNK_SIZE;
		}

		@Override
		protected void processRemaining(ByteBuffer bb) {
			length += bb.remaining();
			int k1 = 0;
			for (int i = 0; bb.hasRemaining(); i += 8) {
				k1 ^= toInt(bb.get()) << i;
			}
			h1 ^= Murmur3_32HashFunction.mixK1(k1);
		}

		@Override
		public HashCode makeHash() {
			return Murmur3_32HashFunction.fmix(h1, length);
		}
	}

	private static final long serialVersionUID = 0L;
}