gemfire-core/src/main/java/com/gemstone/gemfire/cache/hdfs/internal/cardinality/MurmurHash.java

/*=========================================================================
 * Copyright (c) 2010-2014 Pivotal Software, Inc. All Rights Reserved.
 * This product is protected by U.S. and international copyright
 * and intellectual property laws. Pivotal products are covered by
 * one or more patents listed at http://www.pivotal.io/patents.
 *=========================================================================
 */
package com.gemstone.gemfire.cache.hdfs.internal.cardinality;

/**
 * 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.
 */

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup. See http://murmurhash.googlepages.com/ for more details.
 * <p/>
 * <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 hash(Object o)
    {
        if (o == null)
        {
            return 0;
        }
        if (o instanceof Long)
        {
            return hashLong((Long) o);
        }
        if (o instanceof Integer)
        {
            return hashLong((Integer) o);
        }
        if (o instanceof Double)
        {
            return hashLong(Double.doubleToRawLongBits((Double) o));
        }
        if (o instanceof Float)
        {
            return hashLong(Float.floatToRawIntBits((Float) o));
        }
        if (o instanceof String)
        {
            return hash(((String) o).getBytes());
        }
        if (o instanceof byte[])
        {
            return hash((byte[]) o);
        }
        return hash(o.toString());
    }

    public static int hash(byte[] data)
    {
        return hash(data, 0, data.length, -1);
    }

    public static int hash(byte[] data, int seed)
    {
        return hash(data, 0, data.length, seed);
    }

    public static int hash(byte[] 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[offset + i_4 + 3];
            k = k << 8;
            k = k | (data[offset + i_4 + 2] & 0xff);
            k = k << 8;
            k = k | (data[offset + i_4 + 1] & 0xff);
            k = k << 8;
            k = k | (data[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[offset + length - 3] << 16;
            }
            if (left >= 2)
            {
                h ^= (int) data[offset + length - 2] << 8;
            }
            if (left >= 1)
            {
                h ^= (int) data[offset + length - 1];
            }

            h *= m;
        }

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

        return h;
    }

    public static int hashLong(long data)
    {
        int m = 0x5bd1e995;
        int r = 24;

        int h = 0;

        int k = (int) data * m;
        k ^= k >>> r;
        h ^= k * m;

        k = (int) (data >> 32) * m;
        k ^= k >>> r;
        h *= m;
        h ^= k * m;

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

        return h;
    }

    public static long hash64(Object o)
    {
        if (o == null)
        {
            return 0l;
        }
        else if (o instanceof String)
        {
            final byte[] bytes = ((String) o).getBytes();
            return hash64(bytes, bytes.length);
        }
        else if (o instanceof byte[])
        {
            final byte[] bytes = (byte[]) o;
            return hash64(bytes, bytes.length);
        }
        return hash64(o.toString());
    }

    // 64 bit implementation copied from here:  https://github.com/tnm/murmurhash-java

    /**
     * Generates 64 bit hash from byte array with default seed value.
     *
     * @param data   byte array to hash
     * @param length length of the array to hash
     * @return 64 bit hash of the given string
     */
    public static long hash64(final byte[] data, int length)
    {
        return hash64(data, length, 0xe17a1465);
    }


    /**
     * Generates 64 bit hash from byte array of the given length and seed.
     *
     * @param data   byte array to hash
     * @param length length of the array to hash
     * @param seed   initial seed value
     * @return 64 bit hash of the given array
     */
    public static long hash64(final byte[] data, int length, int seed)
    {
        final long m = 0xc6a4a7935bd1e995L;
        final int r = 47;

        long h = (seed & 0xffffffffl) ^ (length * m);

        int length8 = length / 8;

        for (int i = 0; i < length8; i++)
        {
            final int i8 = i * 8;
            long k = ((long) data[i8 + 0] & 0xff) + (((long) data[i8 + 1] & 0xff) << 8)
                    + (((long) data[i8 + 2] & 0xff) << 16) + (((long) data[i8 + 3] & 0xff) << 24)
                    + (((long) data[i8 + 4] & 0xff) << 32) + (((long) data[i8 + 5] & 0xff) << 40)
                    + (((long) data[i8 + 6] & 0xff) << 48) + (((long) data[i8 + 7] & 0xff) << 56);

            k *= m;
            k ^= k >>> r;
            k *= m;

            h ^= k;
            h *= m;
        }

        switch (length % 8)
        {
            case 7:
                h ^= (long) (data[(length & ~7) + 6] & 0xff) << 48;
            case 6:
                h ^= (long) (data[(length & ~7) + 5] & 0xff) << 40;
            case 5:
                h ^= (long) (data[(length & ~7) + 4] & 0xff) << 32;
            case 4:
                h ^= (long) (data[(length & ~7) + 3] & 0xff) << 24;
            case 3:
                h ^= (long) (data[(length & ~7) + 2] & 0xff) << 16;
            case 2:
                h ^= (long) (data[(length & ~7) + 1] & 0xff) << 8;
            case 1:
                h ^= (long) (data[length & ~7] & 0xff);
                h *= m;
        }
        ;

        h ^= h >>> r;
        h *= m;
        h ^= h >>> r;

        return h;
    }
}