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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 }