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 java.io.FileInputStream; 24 import java.io.IOException; 25 26 /** 27 * Produces 32-bit hash for hash table lookup. 28 * 29 * <pre>lookup3.c, by Bob Jenkins, May 2006, Public Domain. 30 * 31 * You can use this free for any purpose. It's in the public domain. 32 * It has no warranty. 33 * </pre> 34 * 35 * @see <a href="http://burtleburtle.net/bob/c/lookup3.c">lookup3.c</a> 36 * @see <a href="http://www.ddj.com/184410284">Hash Functions (and how this 37 * function compares to others such as CRC, MD?, etc</a> 38 * @see <a href="http://burtleburtle.net/bob/hash/doobs.html">Has update on the 39 * Dr. Dobbs Article</a> 40 */ 41 public class JenkinsHash extends Hash { 42 private static long INT_MASK = 0x00000000ffffffffL; 43 private static long BYTE_MASK = 0x00000000000000ffL; 44 45 private static JenkinsHash _instance = new JenkinsHash(); 46 47 public static Hash getInstance() { 48 return _instance; 49 } 50 51 private static long rot(long val, int pos) { 52 return ((Integer.rotateLeft( 53 (int)(val & INT_MASK), pos)) & INT_MASK); 54 } 55 56 /** 57 * taken from hashlittle() -- hash a variable-length key into a 32-bit value 58 * 59 * @param key the key (the unaligned variable-length array of bytes) 60 * @param nbytes number of bytes to include in hash 61 * @param initval can be any integer value 62 * @return a 32-bit value. Every bit of the key affects every bit of the 63 * return value. Two keys differing by one or two bits will have totally 64 * different hash values. 65 * 66 * <p>The best hash table sizes are powers of 2. There is no need to do mod 67 * a prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask. 68 * For example, if you need only 10 bits, do 69 * <code>h = (h & hashmask(10));</code> 70 * In which case, the hash table should have hashsize(10) elements. 71 * 72 * <p>If you are hashing n strings byte[][] k, do it like this: 73 * for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h); 74 * 75 * <p>By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this 76 * code any way you wish, private, educational, or commercial. It's free. 77 * 78 * <p>Use for hash table lookup, or anything where one collision in 2^^32 is 79 * acceptable. Do NOT use for cryptographic purposes. 80 */ 81 @Override 82 @SuppressWarnings("fallthrough") 83 public int hash(byte[] key, int off, int nbytes, int initval) { 84 int length = nbytes; 85 long a, b, c; // We use longs because we don't have unsigned ints 86 a = b = c = (0x00000000deadbeefL + length + initval) & INT_MASK; 87 int offset = off; 88 for (; length > 12; offset += 12, length -= 12) { 89 //noinspection PointlessArithmeticExpression 90 a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK; 91 a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; 92 a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; 93 a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; 94 b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK; 95 b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; 96 b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; 97 b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; 98 c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK; 99 c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; 100 c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; 101 c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; 102 103 /* 104 * mix -- mix 3 32-bit values reversibly. 105 * This is reversible, so any information in (a,b,c) before mix() is 106 * still in (a,b,c) after mix(). 107 * 108 * If four pairs of (a,b,c) inputs are run through mix(), or through 109 * mix() in reverse, there are at least 32 bits of the output that 110 * are sometimes the same for one pair and different for another pair. 111 * 112 * This was tested for: 113 * - pairs that differed by one bit, by two bits, in any combination 114 * of top bits of (a,b,c), or in any combination of bottom bits of 115 * (a,b,c). 116 * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed 117 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as 118 * is commonly produced by subtraction) look like a single 1-bit 119 * difference. 120 * - the base values were pseudorandom, all zero but one bit set, or 121 * all zero plus a counter that starts at zero. 122 * 123 * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that 124 * satisfy this are 125 * 4 6 8 16 19 4 126 * 9 15 3 18 27 15 127 * 14 9 3 7 17 3 128 * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing for 129 * "differ" defined as + with a one-bit base and a two-bit delta. I 130 * used http://burtleburtle.net/bob/hash/avalanche.html to choose 131 * the operations, constants, and arrangements of the variables. 132 * 133 * This does not achieve avalanche. There are input bits of (a,b,c) 134 * that fail to affect some output bits of (a,b,c), especially of a. 135 * The most thoroughly mixed value is c, but it doesn't really even 136 * achieve avalanche in c. 137 * 138 * This allows some parallelism. Read-after-writes are good at doubling 139 * the number of bits affected, so the goal of mixing pulls in the 140 * opposite direction as the goal of parallelism. I did what I could. 141 * Rotates seem to cost as much as shifts on every machine I could lay 142 * my hands on, and rotates are much kinder to the top and bottom bits, 143 * so I used rotates. 144 * 145 * #define mix(a,b,c) \ 146 * { \ 147 * a -= c; a ^= rot(c, 4); c += b; \ 148 * b -= a; b ^= rot(a, 6); a += c; \ 149 * c -= b; c ^= rot(b, 8); b += a; \ 150 * a -= c; a ^= rot(c,16); c += b; \ 151 * b -= a; b ^= rot(a,19); a += c; \ 152 * c -= b; c ^= rot(b, 4); b += a; \ 153 * } 154 * 155 * mix(a,b,c); 156 */ 157 a = (a - c) & INT_MASK; a ^= rot(c, 4); c = (c + b) & INT_MASK; 158 b = (b - a) & INT_MASK; b ^= rot(a, 6); a = (a + c) & INT_MASK; 159 c = (c - b) & INT_MASK; c ^= rot(b, 8); b = (b + a) & INT_MASK; 160 a = (a - c) & INT_MASK; a ^= rot(c,16); c = (c + b) & INT_MASK; 161 b = (b - a) & INT_MASK; b ^= rot(a,19); a = (a + c) & INT_MASK; 162 c = (c - b) & INT_MASK; c ^= rot(b, 4); b = (b + a) & INT_MASK; 163 } 164 165 //-------------------------------- last block: affect all 32 bits of (c) 166 switch (length) { // all the case statements fall through 167 case 12: 168 c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; 169 case 11: 170 c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; 171 case 10: 172 c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; 173 case 9: 174 c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK; 175 case 8: 176 b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; 177 case 7: 178 b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; 179 case 6: 180 b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; 181 case 5: 182 b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK; 183 case 4: 184 a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; 185 case 3: 186 a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; 187 case 2: 188 a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; 189 case 1: 190 //noinspection PointlessArithmeticExpression 191 a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK; 192 break; 193 case 0: 194 return (int)(c & INT_MASK); 195 } 196 /* 197 * final -- final mixing of 3 32-bit values (a,b,c) into c 198 * 199 * Pairs of (a,b,c) values differing in only a few bits will usually 200 * produce values of c that look totally different. This was tested for 201 * - pairs that differed by one bit, by two bits, in any combination 202 * of top bits of (a,b,c), or in any combination of bottom bits of 203 * (a,b,c). 204 * 205 * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed 206 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as 207 * is commonly produced by subtraction) look like a single 1-bit 208 * difference. 209 * 210 * - the base values were pseudorandom, all zero but one bit set, or 211 * all zero plus a counter that starts at zero. 212 * 213 * These constants passed: 214 * 14 11 25 16 4 14 24 215 * 12 14 25 16 4 14 24 216 * and these came close: 217 * 4 8 15 26 3 22 24 218 * 10 8 15 26 3 22 24 219 * 11 8 15 26 3 22 24 220 * 221 * #define final(a,b,c) \ 222 * { 223 * c ^= b; c -= rot(b,14); \ 224 * a ^= c; a -= rot(c,11); \ 225 * b ^= a; b -= rot(a,25); \ 226 * c ^= b; c -= rot(b,16); \ 227 * a ^= c; a -= rot(c,4); \ 228 * b ^= a; b -= rot(a,14); \ 229 * c ^= b; c -= rot(b,24); \ 230 * } 231 * 232 */ 233 c ^= b; c = (c - rot(b,14)) & INT_MASK; 234 a ^= c; a = (a - rot(c,11)) & INT_MASK; 235 b ^= a; b = (b - rot(a,25)) & INT_MASK; 236 c ^= b; c = (c - rot(b,16)) & INT_MASK; 237 a ^= c; a = (a - rot(c,4)) & INT_MASK; 238 b ^= a; b = (b - rot(a,14)) & INT_MASK; 239 c ^= b; c = (c - rot(b,24)) & INT_MASK; 240 241 return (int)(c & INT_MASK); 242 } 243 244 /** 245 * Compute the hash of the specified file 246 * @param args name of file to compute hash of. 247 * @throws IOException e 248 */ 249 public static void main(String[] args) throws IOException { 250 if (args.length != 1) { 251 System.err.println("Usage: JenkinsHash filename"); 252 System.exit(-1); 253 } 254 FileInputStream in = new FileInputStream(args[0]); 255 byte[] bytes = new byte[512]; 256 int value = 0; 257 JenkinsHash hash = new JenkinsHash(); 258 for (int length = in.read(bytes); length > 0 ; length = in.read(bytes)) { 259 value = hash.hash(bytes, length, value); 260 } 261 System.out.println(Math.abs(value)); 262 } 263 }