常见hash算法

/*
 **************************************************************************
 *                                                                        *
 *          General Purpose Hash Function Algorithms Library              *
 *                                                                        *
 * Author: Arash Partow - 2002                                            *
 * URL: http://www.partow.net                                             *
 * URL: http://www.partow.net/programming/hashfunctions/index.html        *
 *                                                                        *
 * Copyright notice:                                                      *
 * Free use of the General Purpose Hash Function Algorithms Library is    *
 * permitted under the guidelines and in accordance with the most current *
 * version of the Common Public License.                                  *
 * http://www.opensource.org/licenses/cpl1.0.php                          *
 *                                                                        *
 **************************************************************************
 */

public class HashUtils {

    public static long RSHash(byte[] bytes, int len) {
        int b = 378551;
        int a = 63689;
        long hash = 0;

        for (int i = 0; i < len; i++) {
            hash = hash * a + bytes[i];
            a = a * b;
        }

        return hash;
    }

    /* End Of RS Hash Function */

    public static long JSHash(byte[] bytes, int len) {
        long hash = 1315423911;

        for (int i = 0; i < len; i++) {
            hash ^= ((hash << 5) + bytes[i] + (hash >> 2));
        }

        return hash;
    }

    /* End Of JS Hash Function */

    public static long PJWHash(byte[] bytes, int len) {
        long BitsInUnsignedInt = (long) (4 * 8);
        long ThreeQuarters = (long) ((BitsInUnsignedInt * 3) / 4);
        long OneEighth = (long) (BitsInUnsignedInt / 8);
        long HighBits = (long) (0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
        long hash = 0;
        long test = 0;

        for (int i = 0; i < len; i++) {
            hash = (hash << OneEighth) + bytes[i];

            if ((test = hash & HighBits) != 0) {
                hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
            }
        }

        return hash;
    }

    /* End Of P. J. Weinberger Hash Function */

    public static long ELFHash(byte[] bytes, int len) {
        long hash = 0;
        long x = 0;

        for (int i = 0; i < len; i++) {
            hash = (hash << 4) + bytes[i];

            if ((x = hash & 0xF0000000L) != 0) {
                hash ^= (x >> 24);
            }
            hash &= ~x;
        }

        return hash;
    }

    /* End Of ELF Hash Function */

    public static long BKDRHash(byte[] bytes, int len) {
        long seed = 131; // 31 131 1313 13131 131313 etc..
        long hash = 0;

        for (int i = 0; i < len; i++) {
            hash = (hash * seed) + bytes[i];
        }

        return hash;
    }

    /* End Of BKDR Hash Function */

    public static long SDBMHash(byte[] bytes, int len) {
        long hash = 0;

        for (int i = 0; i < len; i++) {
            hash = bytes[i] + (hash << 6) + (hash << 16) - hash;
        }

        return hash;
    }

    /* End Of SDBM Hash Function */

    public static long DJBHash(byte[] bytes, int len) {
        long hash = 5381;

        for (int i = 0; i < len; i++) {
            hash = ((hash << 5) + hash) + bytes[i];
        }

        return hash;
    }

    /* End Of DJB Hash Function */

    public static long DEKHash(byte[] bytes, int len) {
        long hash = len;

        for (int i = 0; i < len; i++) {
            hash = ((hash << 5) ^ (hash >> 27)) ^ bytes[i];
        }

        return hash;
    }

    /* End Of DEK Hash Function */

    public static long BPHash(byte[] bytes, int len) {
        long hash = 0;

        for (int i = 0; i < len; i++) {
            hash = hash << 7 ^ bytes[i];
        }

        return hash;
    }

    /* End Of BP Hash Function */

    public static long FNVHash(byte[] bytes, int len) {
        long fnv_prime = 0x811C9DC5;
        long hash = 0;

        for (int i = 0; i < len; i++) {
            hash *= fnv_prime;
            hash ^= bytes[i];
        }

        return hash;
    }

    /* End Of FNV Hash Function */

    public static long APHash(byte[] bytes, int len) {
        long hash = 0xAAAAAAAA;

        for (int i = 0; i < len; i++) {
            if ((i & 1) == 0) {
                hash ^= ((hash << 7) ^ bytes[i] * (hash >> 3));
            } else {
                hash ^= (~((hash << 11) + (bytes[i] & 0xFF) ^ (hash >> 5)));
            }
        }

        return hash;
    }
    /* End Of AP Hash Function */

}