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Java > Open Source Codes > com > db4o > foundation > BitMap4


1 /* Copyright (C) 2004 - 2006 db4objects Inc. http://www.db4o.com
2
3 This file is part of the db4o open source object database.
4
5 db4o is free software; you can redistribute it and/or modify it under
6 the terms of version 2 of the GNU General Public License as published
7 by the Free Software Foundation and as clarified by db4objects' GPL
8 interpretation policy, available at
9 http://www.db4o.com/about/company/legalpolicies/gplinterpretation/
10 Alternatively you can write to db4objects, Inc., 1900 S Norfolk Street,
11 Suite 350, San Mateo, CA 94403, USA.
12
13 db4o is distributed in the hope that it will be useful, but WITHOUT ANY
14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
15 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 for more details.
17
18 You should have received a copy of the GNU General Public License along
19 with this program; if not, write to the Free Software Foundation, Inc.,
20 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */

21 package com.db4o.foundation;
22
23
24 /**
25  * @exclude
26  */

27 public final class BitMap4 {
28     
29     private final byte[] _bits;
30     
31     public BitMap4(int numBits){
32         _bits = new byte[byteCount(numBits)];
33     }
34
35     /** "readFrom buffer" constructor **/
36     public BitMap4(byte[] buffer, int pos, int numBits){
37         this(numBits);
38         System.arraycopy(buffer, pos, _bits, 0, _bits.length);
39     }
40     
41     public boolean isTrue(int bit) {
42         return ((_bits[arrayOffset(bit)]>>>byteOffset(bit))&1)!=0;
43     }
44
45     public int marshalledLength(){
46         return _bits.length;
47     }
48     
49     public void setFalse(int bit){
50         _bits[arrayOffset(bit)] &= (byte)~bitMask(bit);
51     }
52     
53     public void setTrue(int bit){
54         _bits[arrayOffset(bit)] |= bitMask(bit);
55     }
56     
57     public void writeTo(byte[] bytes, int pos){
58         System.arraycopy(_bits, 0, bytes, pos, _bits.length);
59     }
60     
61     private byte byteOffset(int bit) {
62         return (byte)(bit % 8);
63     }
64
65     private int arrayOffset(int bit) {
66         return bit / 8;
67     }
68     
69     private byte bitMask(int bit) {
70         return (byte)(1 << byteOffset(bit));
71     }
72     
73     private int byteCount(int numBits) {
74         return (numBits + 7) / 8;
75     }
76 }
77
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