1 /** 2 * Copyright 2010 The Apache Software Foundation 3 * 4 * Licensed to the Apache Software Foundation (ASF) under one 5 * or more contributor license agreements. See the NOTICE file 6 * distributed with this work for additional information 7 * regarding copyright ownership. The ASF licenses this file 8 * to you under the Apache License, Version 2.0 (the 9 * "License"); you may not use this file except in compliance 10 * with the License. You may obtain a copy of the License at 11 * 12 * http://www.apache.org/licenses/LICENSE-2.0 13 * 14 * Unless required by applicable law or agreed to in writing, software 15 * distributed under the License is distributed on an "AS IS" BASIS, 16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 17 * See the License for the specific language governing permissions and 18 * limitations under the License. 19 */ 20 21 package org.apache.hadoop.hbase.util; 22 23 import static java.lang.Integer.rotateLeft; 24 25 import java.io.FileInputStream; 26 import java.io.IOException; 27 28 /** 29 * Produces 32-bit hash for hash table lookup. 30 * 31 * <pre>lookup3.c, by Bob Jenkins, May 2006, Public Domain. 32 * 33 * You can use this free for any purpose. It's in the public domain. 34 * It has no warranty. 35 * </pre> 36 * 37 * @see <a href="http://burtleburtle.net/bob/c/lookup3.c">lookup3.c</a> 38 * @see <a href="http://www.ddj.com/184410284">Hash Functions (and how this 39 * function compares to others such as CRC, MD?, etc</a> 40 * @see <a href="http://burtleburtle.net/bob/hash/doobs.html">Has update on the 41 * Dr. Dobbs Article</a> 42 */ 43 public class JenkinsHash extends Hash { 44 private static final int BYTE_MASK = 0xff; 45 46 private static JenkinsHash _instance = new JenkinsHash(); 47 48 public static Hash getInstance() { 49 return _instance; 50 } 51 52 /** 53 * taken from hashlittle() -- hash a variable-length key into a 32-bit value 54 * 55 * @param key the key (the unaligned variable-length array of bytes) 56 * @param nbytes number of bytes to include in hash 57 * @param initval can be any integer value 58 * @return a 32-bit value. Every bit of the key affects every bit of the 59 * return value. Two keys differing by one or two bits will have totally 60 * different hash values. 61 * 62 * <p>The best hash table sizes are powers of 2. There is no need to do mod 63 * a prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask. 64 * For example, if you need only 10 bits, do 65 * <code>h = (h & hashmask(10));</code> 66 * In which case, the hash table should have hashsize(10) elements. 67 * 68 * <p>If you are hashing n strings byte[][] k, do it like this: 69 * for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h); 70 * 71 * <p>By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this 72 * code any way you wish, private, educational, or commercial. It's free. 73 * 74 * <p>Use for hash table lookup, or anything where one collision in 2^^32 is 75 * acceptable. Do NOT use for cryptographic purposes. 76 */ 77 @Override 78 @SuppressWarnings("fallthrough") 79 public int hash(byte[] key, int off, int nbytes, int initval) { 80 int length = nbytes; 81 int a, b, c; 82 a = b = c = 0xdeadbeef + length + initval; 83 int offset = off; 84 for (; length > 12; offset += 12, length -= 12) { 85 a += (key[offset] & BYTE_MASK); 86 a += ((key[offset + 1] & BYTE_MASK) << 8); 87 a += ((key[offset + 2] & BYTE_MASK) << 16); 88 a += ((key[offset + 3] & BYTE_MASK) << 24); 89 b += (key[offset + 4] & BYTE_MASK); 90 b += ((key[offset + 5] & BYTE_MASK) << 8); 91 b += ((key[offset + 6] & BYTE_MASK) << 16); 92 b += ((key[offset + 7] & BYTE_MASK) << 24); 93 c += (key[offset + 8] & BYTE_MASK); 94 c += ((key[offset + 9] & BYTE_MASK) << 8); 95 c += ((key[offset + 10] & BYTE_MASK) << 16); 96 c += ((key[offset + 11] & BYTE_MASK) << 24); 97 98 /* 99 * mix -- mix 3 32-bit values reversibly. 100 * This is reversible, so any information in (a,b,c) before mix() is 101 * still in (a,b,c) after mix(). 102 * 103 * If four pairs of (a,b,c) inputs are run through mix(), or through 104 * mix() in reverse, there are at least 32 bits of the output that 105 * are sometimes the same for one pair and different for another pair. 106 * 107 * This was tested for: 108 * - pairs that differed by one bit, by two bits, in any combination 109 * of top bits of (a,b,c), or in any combination of bottom bits of 110 * (a,b,c). 111 * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed 112 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as 113 * is commonly produced by subtraction) look like a single 1-bit 114 * difference. 115 * - the base values were pseudorandom, all zero but one bit set, or 116 * all zero plus a counter that starts at zero. 117 * 118 * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that 119 * satisfy this are 120 * 4 6 8 16 19 4 121 * 9 15 3 18 27 15 122 * 14 9 3 7 17 3 123 * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing for 124 * "differ" defined as + with a one-bit base and a two-bit delta. I 125 * used http://burtleburtle.net/bob/hash/avalanche.html to choose 126 * the operations, constants, and arrangements of the variables. 127 * 128 * This does not achieve avalanche. There are input bits of (a,b,c) 129 * that fail to affect some output bits of (a,b,c), especially of a. 130 * The most thoroughly mixed value is c, but it doesn't really even 131 * achieve avalanche in c. 132 * 133 * This allows some parallelism. Read-after-writes are good at doubling 134 * the number of bits affected, so the goal of mixing pulls in the 135 * opposite direction as the goal of parallelism. I did what I could. 136 * Rotates seem to cost as much as shifts on every machine I could lay 137 * my hands on, and rotates are much kinder to the top and bottom bits, 138 * so I used rotates. 139 * 140 * #define mix(a,b,c) \ 141 * { \ 142 * a -= c; a ^= rot(c, 4); c += b; \ 143 * b -= a; b ^= rot(a, 6); a += c; \ 144 * c -= b; c ^= rot(b, 8); b += a; \ 145 * a -= c; a ^= rot(c,16); c += b; \ 146 * b -= a; b ^= rot(a,19); a += c; \ 147 * c -= b; c ^= rot(b, 4); b += a; \ 148 * } 149 * 150 * mix(a,b,c); 151 */ 152 a -= c; a ^= rotateLeft(c, 4); c += b; 153 b -= a; b ^= rotateLeft(a, 6); a += c; 154 c -= b; c ^= rotateLeft(b, 8); b += a; 155 a -= c; a ^= rotateLeft(c, 16); c += b; 156 b -= a; b ^= rotateLeft(a, 19); a += c; 157 c -= b; c ^= rotateLeft(b, 4); b += a; 158 } 159 160 //-------------------------------- last block: affect all 32 bits of (c) 161 switch (length) { // all the case statements fall through 162 case 12: 163 c += ((key[offset + 11] & BYTE_MASK) << 24); 164 case 11: 165 c += ((key[offset + 10] & BYTE_MASK) << 16); 166 case 10: 167 c += ((key[offset + 9] & BYTE_MASK) << 8); 168 case 9: 169 c += (key[offset + 8] & BYTE_MASK); 170 case 8: 171 b += ((key[offset + 7] & BYTE_MASK) << 24); 172 case 7: 173 b += ((key[offset + 6] & BYTE_MASK) << 16); 174 case 6: 175 b += ((key[offset + 5] & BYTE_MASK) << 8); 176 case 5: 177 b += (key[offset + 4] & BYTE_MASK); 178 case 4: 179 a += ((key[offset + 3] & BYTE_MASK) << 24); 180 case 3: 181 a += ((key[offset + 2] & BYTE_MASK) << 16); 182 case 2: 183 a += ((key[offset + 1] & BYTE_MASK) << 8); 184 case 1: 185 //noinspection PointlessArithmeticExpression 186 a += (key[offset + 0] & BYTE_MASK); 187 break; 188 case 0: 189 return c; 190 } 191 /* 192 * final -- final mixing of 3 32-bit values (a,b,c) into c 193 * 194 * Pairs of (a,b,c) values differing in only a few bits will usually 195 * produce values of c that look totally different. This was tested for 196 * - pairs that differed by one bit, by two bits, in any combination 197 * of top bits of (a,b,c), or in any combination of bottom bits of 198 * (a,b,c). 199 * 200 * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed 201 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as 202 * is commonly produced by subtraction) look like a single 1-bit 203 * difference. 204 * 205 * - the base values were pseudorandom, all zero but one bit set, or 206 * all zero plus a counter that starts at zero. 207 * 208 * These constants passed: 209 * 14 11 25 16 4 14 24 210 * 12 14 25 16 4 14 24 211 * and these came close: 212 * 4 8 15 26 3 22 24 213 * 10 8 15 26 3 22 24 214 * 11 8 15 26 3 22 24 215 * 216 * #define final(a,b,c) \ 217 * { 218 * c ^= b; c -= rot(b,14); \ 219 * a ^= c; a -= rot(c,11); \ 220 * b ^= a; b -= rot(a,25); \ 221 * c ^= b; c -= rot(b,16); \ 222 * a ^= c; a -= rot(c,4); \ 223 * b ^= a; b -= rot(a,14); \ 224 * c ^= b; c -= rot(b,24); \ 225 * } 226 * 227 */ 228 c ^= b; c -= rotateLeft(b, 14); 229 a ^= c; a -= rotateLeft(c, 11); 230 b ^= a; b -= rotateLeft(a, 25); 231 c ^= b; c -= rotateLeft(b, 16); 232 a ^= c; a -= rotateLeft(c, 4); 233 b ^= a; b -= rotateLeft(a, 14); 234 c ^= b; c -= rotateLeft(b, 24); 235 return c; 236 } 237 238 /** 239 * Compute the hash of the specified file 240 * @param args name of file to compute hash of. 241 * @throws IOException e 242 */ 243 public static void main(String[] args) throws IOException { 244 if (args.length != 1) { 245 System.err.println("Usage: JenkinsHash filename"); 246 System.exit(-1); 247 } 248 FileInputStream in = new FileInputStream(args[0]); 249 byte[] bytes = new byte[512]; 250 int value = 0; 251 JenkinsHash hash = new JenkinsHash(); 252 for (int length = in.read(bytes); length > 0; length = in.read(bytes)) { 253 value = hash.hash(bytes, length, value); 254 } 255 System.out.println(Math.abs(value)); 256 } 257 }