MurmurHash.java

package org.videolan.vlc.util;

/** Murmur hash 2.0.
 *
 * The murmur hash is a relative fast hash function from
 * http://murmurhash.googlepages.com/ for platforms with efficient
 * multiplication.
 *
 * This is a re-implementation of the original C code plus some
 * additional features.
 *
 * Public domain.
 *
 * @author Viliam Holub
 * @version 1.0.2
 *
 */
public final class MurmurHash {

    /** Generates 32 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 32 bit hash of the given array
     */
    public static int hash32(final 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;
    }

    /** Generates 32 bit hash from byte array with default seed value.
     *
     * @param data byte array to hash
     * @param length length of the array to hash
     * @return 32 bit hash of the given array
     */
    public static int hash32(final byte[] data, int length) {
        return hash32(data, length, 0x9747b28c);
    }

    /** Generates 32 bit hash from a string.
     *
     * @param text string to hash
     * @return 32 bit hash of the given string
     */
    public static int hash32(final String text) {
        final byte[] bytes = text.getBytes();
        return hash32(bytes, bytes.length);
    }

    /** Generates 32 bit hash from a substring.
     *
     * @param text string to hash
     * @param from starting index
     * @param length length of the substring to hash
     * @return 32 bit hash of the given string
     */
    public static int hash32(final String text, int from, int length) {
        return hash32(text.substring(from, from + length));
    }

    /** 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;
    }

    /** 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 a string.
     *
     * @param text string to hash
     * @return 64 bit hash of the given string
     */
    public static long hash64(final String text) {
        final byte[] bytes = text.getBytes();
        return hash64(bytes, bytes.length);
    }

    /** Generates 64 bit hash from a substring.
     *
     * @param text string to hash
     * @param from starting index
     * @param length length of the substring to hash
     * @return 64 bit hash of the given array
     */
    public static long hash64(final String text, int from, int length) {
        return hash64(text.substring(from, from + length));
    }
}