Java example source code file (Murmur3.java)

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Java - Java tags/keywords

murmur3, nio

The Murmur3.java Java example source code

/*
 * 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:
 * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
 * (Modified to adapt to Guava coding conventions and to use the HashFunction interface)
 */

/**
 * Modified to remove stuff Clojure doesn't need, placed under clojure.lang namespace,
 * all fns made static, added hashOrdered/Unordered
 */

package clojure.lang;

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

/**
 * See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
 * MurmurHash3_x86_32
 *
 * @author Austin Appleby
 * @author Dimitris Andreou
 * @author Kurt Alfred Kluever
 */

public final class Murmur3{
private static final int seed = 0;
private static final int C1 = 0xcc9e2d51;
private static final int C2 = 0x1b873593;

public static int hashInt(int input){
	if(input == 0) return 0;
	int k1 = mixK1(input);
	int h1 = mixH1(seed, k1);

	return fmix(h1, 4);
}

public static int hashLong(long input){
	if(input == 0) return 0;
	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, 8);
}

public static int 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, 2 * input.length());
}

public static int mixCollHash(int hash, int count){
	int h1 = seed;
	int k1 = mixK1(hash);
	h1 = mixH1(h1, k1);
	return fmix(h1, count);
}

public static int hashOrdered(Iterable xs){
	int n = 0;
	int hash = 1;

	for(Object x : xs)
		{
		hash = 31 * hash + Util.hasheq(x);
		++n;
		}

	return mixCollHash(hash, n);
}

public static int hashUnordered(Iterable xs){
	int hash = 0;
	int n = 0;
	for(Object x : xs)
		{
		hash += Util.hasheq(x);
		++n;
		}	

	return mixCollHash(hash, n);
}

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 int fmix(int h1, int length){
	h1 ^= length;
	h1 ^= h1 >>> 16;
	h1 *= 0x85ebca6b;
	h1 ^= h1 >>> 13;
	h1 *= 0xc2b2ae35;
	h1 ^= h1 >>> 16;
	return h1;
}

}