| /** |
| * 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. |
| * <p> |
| * <p>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 |
| * <code>h = (h & hashmask(10));</code> |
| * In which case, the hash table should have hashsize(10) elements. |
| * <p> |
| * <p>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); |
| * <p> |
| * <p>By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this |
| * code any way you wish, private, educational, or commercial. It's free. |
| * <p> |
| * <p>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); |
| } |
| |
| } |
