MurmurHash.java

package org.wikibrain.utils;

/**
 * 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.
 */

/**
 *
 * Adapted from Clearspring's stream-lib https://github.com/addthis/stream-lib/
 * by Shilad Sen.
 *
 * <p>
 * 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 long hash64(String s) {
        final byte[] bytes = s.getBytes();
        return hash64(bytes, bytes.length);
    }

    // 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;
    }
}