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Java > Open Source Codes > gov > nasa > jpf > util > HashData


1 //
2 // Copyright (C) 2005 United States Government as represented by the
3 // Administrator of the National Aeronautics and Space Administration
4 // (NASA). All Rights Reserved.
5 //
6 // This software is distributed under the NASA Open Source Agreement
7 // (NOSA), version 1.3. The NOSA has been approved by the Open Source
8 // Initiative. See the file NOSA-1.3-JPF at the top of the distribution
9 // directory tree for the complete NOSA document.
10 //
11 // THE SUBJECT SOFTWARE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY OF ANY
12 // KIND, EITHER EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT
13 // LIMITED TO, ANY WARRANTY THAT THE SUBJECT SOFTWARE WILL CONFORM TO
14 // SPECIFICATIONS, ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR
15 // A PARTICULAR PURPOSE, OR FREEDOM FROM INFRINGEMENT, ANY WARRANTY THAT
16 // THE SUBJECT SOFTWARE WILL BE ERROR FREE, OR ANY WARRANTY THAT
17 // DOCUMENTATION, IF PROVIDED, WILL CONFORM TO THE SUBJECT SOFTWARE.
18 //
19 package gov.nasa.jpf.util;
20
21 /**
22  * object to compute complex hash values that can be accumulated and
23  * delegated (to aggregates etc.)
24  * used to obtain hashcodes for states
25  */
26 public class HashData {
27   private int poly = 0x88888EEF;
28   private int m = -1;
29
30   public int getValue () {
31     return (m >>> 4) ^ (m & 15);
32   }
33
34   public void add (int value) {
35     if (m < 0) {
36       m += m;
37       m ^= poly;
38     } else {
39       m += m;
40     }
41
42     m ^= value;
43   }
44
45   public void add (String JavaDoc s) {
46     // probably a bit too simplistic (the Java String hashing isn't stellar)
47 if (s != null) {
48       add(s.hashCode());
49     }
50   }
51
52   public void add (boolean b) {
53     // a clear case of '42', but that's the "official" boolean hashing
54 add(b ? 1231 : 1237);
55   }
56 }
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