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/**
 * 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.
 */
package org.apache.activemq.util;

public class JenkinsHash {

    private static final long INT_MASK = 0x00000000ffffffffL;
    private static final long BYTE_MASK = 0x00000000000000ffL;

    private static final JenkinsHash _instance = new JenkinsHash();

    public static JenkinsHash getInstance() {
        return _instance;
    }

    private static long rot(long val, int pos) {
        return ((Integer.rotateLeft((int) (val & INT_MASK), pos)) & INT_MASK);
    }

    /**
     * Calculate a hash using all bytes from the input argument, and
     * a seed of -1.
     * @param bytes input bytes
     * @return hash value
     */
    public int hash(byte[] bytes) {
        return hash(bytes, bytes.length, -1);
    }

    /**
     * Calculate a hash using all bytes from the input argument, and
     * a seed of -1.
     * @param bytes input bytes
     * @return hash value
     */
    public int hash(byte[] bytes, int initVal) {
        return hash(bytes, bytes.length, initVal);
    }

    /**
     * taken from  hashlittle() -- hash a variable-length key into a 32-bit value
     *
     * @param key     the key (the unaligned variable-length array of bytes)
     * @param nbytes  number of bytes to include in hash
     * @param initval can be any integer value
     * @return a 32-bit value.  Every bit of the key affects every bit of the
     * return value.  Two keys differing by one or two bits will have totally
     * different hash values.
     * 

*

The best hash table sizes are powers of 2. There is no need to do mod * a prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask. * For example, if you need only 10 bits, do * h = (h & hashmask(10)); * In which case, the hash table should have hashsize(10) elements. *

*

If you are hashing n strings byte[][] k, do it like this: * for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h); *

*

By Bob Jenkins, 2006. [email protected]. You may use this * code any way you wish, private, educational, or commercial. It's free. *

*

Use for hash table lookup, or anything where one collision in 2^^32 is * acceptable. Do NOT use for cryptographic purposes. */ public int hash(byte[] key, int nbytes, int initval) { int length = nbytes; long a, b, c; // We use longs because we don't have unsigned ints a = b = c = (0x00000000deadbeefL + length + initval) & INT_MASK; int offset = 0; for (; length > 12; offset += 12, length -= 12) { a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK; a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK; b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK; c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; /* * mix -- mix 3 32-bit values reversibly. * This is reversible, so any information in (a,b,c) before mix() is * still in (a,b,c) after mix(). * * If four pairs of (a,b,c) inputs are run through mix(), or through * mix() in reverse, there are at least 32 bits of the output that * are sometimes the same for one pair and different for another pair. * * This was tested for: * - pairs that differed by one bit, by two bits, in any combination * of top bits of (a,b,c), or in any combination of bottom bits of * (a,b,c). * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as * is commonly produced by subtraction) look like a single 1-bit * difference. * - the base values were pseudorandom, all zero but one bit set, or * all zero plus a counter that starts at zero. * * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that * satisfy this are * 4 6 8 16 19 4 * 9 15 3 18 27 15 * 14 9 3 7 17 3 * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing for * "differ" defined as + with a one-bit base and a two-bit delta. I * used http://burtleburtle.net/bob/hash/avalanche.html to choose * the operations, constants, and arrangements of the variables. * * This does not achieve avalanche. There are input bits of (a,b,c) * that fail to affect some output bits of (a,b,c), especially of a. * The most thoroughly mixed value is c, but it doesn't really even * achieve avalanche in c. * * This allows some parallelism. Read-after-writes are good at doubling * the number of bits affected, so the goal of mixing pulls in the * opposite direction as the goal of parallelism. I did what I could. * Rotates seem to cost as much as shifts on every machine I could lay * my hands on, and rotates are much kinder to the top and bottom bits, * so I used rotates. * * #define mix(a,b,c) \ * { \ * a -= c; a ^= rot(c, 4); c += b; \ * b -= a; b ^= rot(a, 6); a += c; \ * c -= b; c ^= rot(b, 8); b += a; \ * a -= c; a ^= rot(c,16); c += b; \ * b -= a; b ^= rot(a,19); a += c; \ * c -= b; c ^= rot(b, 4); b += a; \ * } * * mix(a,b,c); */ a = (a - c) & INT_MASK; a ^= rot(c, 4); c = (c + b) & INT_MASK; b = (b - a) & INT_MASK; b ^= rot(a, 6); a = (a + c) & INT_MASK; c = (c - b) & INT_MASK; c ^= rot(b, 8); b = (b + a) & INT_MASK; a = (a - c) & INT_MASK; a ^= rot(c, 16); c = (c + b) & INT_MASK; b = (b - a) & INT_MASK; b ^= rot(a, 19); a = (a + c) & INT_MASK; c = (c - b) & INT_MASK; c ^= rot(b, 4); b = (b + a) & INT_MASK; } //-------------------------------- last block: affect all 32 bits of (c) switch (length) { // all the case statements fall through case 12: c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; case 11: c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; case 10: c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; case 9: c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK; case 8: b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; case 7: b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; case 6: b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; case 5: b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK; case 4: a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; case 3: a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; case 2: a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; case 1: a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK; break; case 0: return (int) (c & INT_MASK); } /* * final -- final mixing of 3 32-bit values (a,b,c) into c * * Pairs of (a,b,c) values differing in only a few bits will usually * produce values of c that look totally different. This was tested for * - pairs that differed by one bit, by two bits, in any combination * of top bits of (a,b,c), or in any combination of bottom bits of * (a,b,c). * * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as * is commonly produced by subtraction) look like a single 1-bit * difference. * * - the base values were pseudorandom, all zero but one bit set, or * all zero plus a counter that starts at zero. * * These constants passed: * 14 11 25 16 4 14 24 * 12 14 25 16 4 14 24 * and these came close: * 4 8 15 26 3 22 24 * 10 8 15 26 3 22 24 * 11 8 15 26 3 22 24 * * #define final(a,b,c) \ * { * c ^= b; c -= rot(b,14); \ * a ^= c; a -= rot(c,11); \ * b ^= a; b -= rot(a,25); \ * c ^= b; c -= rot(b,16); \ * a ^= c; a -= rot(c,4); \ * b ^= a; b -= rot(a,14); \ * c ^= b; c -= rot(b,24); \ * } * */ c ^= b; c = (c - rot(b, 14)) & INT_MASK; a ^= c; a = (a - rot(c, 11)) & INT_MASK; b ^= a; b = (b - rot(a, 25)) & INT_MASK; c ^= b; c = (c - rot(b, 16)) & INT_MASK; a ^= c; a = (a - rot(c, 4)) & INT_MASK; b ^= a; b = (b - rot(a, 14)) & INT_MASK; c ^= b; c = (c - rot(b, 24)) & INT_MASK; return (int) (c & INT_MASK); } }





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