HashCalculator.java

package com.cse10.duplicateDetector;

import java.nio.ByteBuffer;
import java.nio.charset.Charset;

/**
 * this class is used to create 32bits and 64bits hash values for given string
 * this is murmur hash function. it is non-cryptographic hash function
 * Created by Chamath on 1/2/2015.
 */
public class HashCalculator {

    /**
     * calculate 32 bit hash value for given word
     *
     * @param document
     * @return
     */
    public int getHash32Value(String document) {
        //Each character is encoded as a 8 bit unit. Each byte of the buffer represents a character.
        //buffer length is equal to the length of the word
        byte[] buffer = document.getBytes(Charset.forName("utf-8"));
        return hash32(buffer, buffer.length, 0);
    }

    /**
     * calculate 64 bit hash value for given word
     *
     * @param document
     * @return
     */
    public long getHash64Value(String document) {
        //Each character is encoded as a 8 bit unit. Each byte of the buffer represents a character.
        //buffer length is equal to the length of the word
        byte[] buffer = document.getBytes(Charset.forName("utf-8"));
        return hash64(buffer, buffer.length, 0);
    }


    /**
     * implemented by Viliam Holub
     * https://github.com/tnm/murmurhash-java/blob/master/src/main/java/ie/ucd/murmur/MurmurHash.java
     * generate 32 bit hash from given byte buffer
     *
     * @param data
     * @param length
     * @param seed
     * @return
     */
    private int hash32(byte[] data, int length, int seed) {
        // 'm' and 'r' are mixing constants generated offline.
        // They're not really 'magic', they just happen to work well.
        final int m = 0x5bd1e995;
        final int r = 24;

        // Initialize the hash to a random value
        int h = seed ^ length;
        int length4 = length / 4;

        for (int i = 0; i < length4; i++) {
            final int i4 = i * 4;
            int k = (data[i4 + 0] & 0xff) + ((data[i4 + 1] & 0xff) << 8)
                    + ((data[i4 + 2] & 0xff) << 16) + ((data[i4 + 3] & 0xff) << 24);
            k *= m;
            k ^= k >>> r;
            k *= m;
            h *= m;
            h ^= k;
        }

        // Handle the last few bytes of the input array
        switch (length % 4) {
            case 3:
                h ^= (data[(length & ~3) + 2] & 0xff) << 16;
            case 2:
                h ^= (data[(length & ~3) + 1] & 0xff) << 8;
            case 1:
                h ^= (data[length & ~3] & 0xff);
                h *= m;
        }

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

        return h;
    }

    /**
     * implemented by Viliam Holub
     * https://github.com/tnm/murmurhash-java/blob/master/src/main/java/ie/ucd/murmur/MurmurHash.java
     * generate 64 bit hash from given byte buffer
     *
     * @param data
     * @param length
     * @param seed
     * @return
     */
    private 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;
    }

}