MurmurHash.java

/**
 * 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 org.apache.cassandra.utils;

import java.nio.ByteBuffer;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup. See http://murmurhash.googlepages.com/ for more details.
 * 
 * <p>
 * The C version of MurmurHash 2.0 found at that site was ported to Java by
 * Andrzej Bialecki (ab at getopt org).
 * </p>
 */
public class MurmurHash
{
    public static int hash32(ByteBuffer data, int offset, int length, int seed)
    {
        int m = 0x5bd1e995;
        int r = 24;

        int h = seed ^ length;

        int len_4 = length >> 2;

        for (int i = 0; i < len_4; i++)
        {
            int i_4 = i << 2;
            int k = data.get(offset + i_4 + 3);
            k = k << 8;
            k = k | (data.get(offset + i_4 + 2) & 0xff);
            k = k << 8;
            k = k | (data.get(offset + i_4 + 1) & 0xff);
            k = k << 8;
            k = k | (data.get(offset + i_4 + 0) & 0xff);
            k *= m;
            k ^= k >>> r;
            k *= m;
            h *= m;
            h ^= k;
        }

        // avoid calculating modulo
        int len_m = len_4 << 2;
        int left = length - len_m;

        if (left != 0)
        {
            if (left >= 3)
            {
                h ^= (int) data.get(offset + length - 3) << 16;
            }
            if (left >= 2)
            {
                h ^= (int) data.get(offset + length - 2) << 8;
            }
            if (left >= 1)
            {
                h ^= (int) data.get(offset + length - 1);
            }

            h *= m;
        }

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

        return h;
    }

    public static long hash64(ByteBuffer key, int offset, int length, long seed)
    {
        long m64 = 0xc6a4a7935bd1e995L;
        int r64 = 47;

        long h64 = (seed & 0xffffffffL) ^ (m64 * length);

        int lenLongs = length >> 3;

        for (int i = 0; i < lenLongs; ++i)
        {
            int i_8 = i << 3;

            long k64 =  ((long)  key.get(offset+i_8+0) & 0xff)      + (((long) key.get(offset+i_8+1) & 0xff)<<8)  +
			            (((long) key.get(offset+i_8+2) & 0xff)<<16) + (((long) key.get(offset+i_8+3) & 0xff)<<24) +
			            (((long) key.get(offset+i_8+4) & 0xff)<<32) + (((long) key.get(offset+i_8+5) & 0xff)<<40) +
			            (((long) key.get(offset+i_8+6) & 0xff)<<48) + (((long) key.get(offset+i_8+7) & 0xff)<<56);
           
            k64 *= m64;
            k64 ^= k64 >>> r64;
            k64 *= m64;

            h64 ^= k64;
            h64 *= m64;
        }

        int rem = length & 0x7;

        switch (rem)
        {
        case 0:
            break;
        case 7:
            h64 ^= (long) key.get(offset + length - rem + 6) << 48;
        case 6:
            h64 ^= (long) key.get(offset + length - rem + 5) << 40;
        case 5:
            h64 ^= (long) key.get(offset + length - rem + 4) << 32;
        case 4:
            h64 ^= (long) key.get(offset + length - rem + 3) << 24;
        case 3:
            h64 ^= (long) key.get(offset + length - rem + 2) << 16;
        case 2:
            h64 ^= (long) key.get(offset + length - rem + 1) << 8;
        case 1:
            h64 ^= (long) key.get(offset + length - rem);
            h64 *= m64;
        }

        h64 ^= h64 >>> r64;
        h64 *= m64;
        h64 ^= h64 >>> r64;

        return h64;
    }
}