MurmurHash3UDF.java

package brickhouse.udf.collect;

/**
 * This code is public domain.
 *
 * MurmurHash3 was written by Austin Appleby and put into the
 * public domain. The author hereby disclaims copyright to this
 * source code. See http://code.google.com/p/smhasher
 *
 * The java port for MurmurHash3 found here was authored by
 * Yonik Seeley and was placed into the public domain per
 * https://github.com/yonik/java_util/blob/master/src/util/hash/MurmurHash3.java
 *
 * This MurmurHash3 Hive UDF was authored by Vangie Shue
 * and is placed in the public domain.
 *
 **/

import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;

/**
 * Evaluates the 32 bit x86 version of MurmurHash3 of Text input.
 * Passing a seed value is optional, the default seed used is 1.
 * Offset is set to 0.
 */

public class MurmurHash3UDF extends UDF {

    public Integer evaluate(Text input) {
        if (input == null) {
            return null;
        }

        return hash_str(input.toString());
    }

    public Integer evaluate(Text input, IntWritable seed) {
        if (input == null) {
            return null;
        }

        return hash_str(input.toString(), seed.get());
    }

    private static int hash_str(String item) {
        // Offset: 0
        // Seed: 1
        return mhash(item.getBytes(), 0, item.length(), 1);
    }

    private static int hash_str(String item, int seed) {
        // Offset: 0
        return mhash(item.getBytes(), 0, item.length(), seed);
    }

    private static int mhash(byte[] data, int offset, int len, int seed) {

        int c1 = 0xcc9e2d51;
        int c2 = 0x1b873593;

        int h1 = seed;
        int roundedEnd = offset + (len & 0xfffffffc);  // round down to 4 byte block

        for (int i = offset; i < roundedEnd; i += 4) {
            // little endian load order
            int k1 = (data[i] & 0xff) | ((data[i + 1] & 0xff) << 8) | ((data[i + 2] & 0xff) << 16) | (data[i + 3] << 24);
            k1 *= c1;
            k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
            k1 *= c2;

            h1 ^= k1;
            h1 = (h1 << 13) | (h1 >>> 19);  // ROTL32(h1,13);
            h1 = h1 * 5 + 0xe6546b64;
        }

        // tail
        int k1 = 0;

        switch (len & 0x03) {
            case 3:
                k1 = (data[roundedEnd + 2] & 0xff) << 16;
                // fallthrough
            case 2:
                k1 |= (data[roundedEnd + 1] & 0xff) << 8;
                // fallthrough
            case 1:
                k1 |= data[roundedEnd] & 0xff;
                k1 *= c1;
                k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
                k1 *= c2;
                h1 ^= k1;
            default:
        }

        // finalization
        h1 ^= len;

        // fmix(h1);
        h1 ^= h1 >>> 16;
        h1 *= 0x85ebca6b;
        h1 ^= h1 >>> 13;
        h1 *= 0xc2b2ae35;
        h1 ^= h1 >>> 16;

        return h1;
    }

}