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1   /**
2    * JDBM LICENSE v1.00
3    *
4    * Redistribution and use of this software and associated documentation
5    * ("Software"), with or without modification, are permitted provided
6    * that the following conditions are met:
7    *
8    * 1. Redistributions of source code must retain copyright
9    *    statements and notices.  Redistributions must also contain a
10   *    copy of this document.
11   *
12   * 2. Redistributions in binary form must reproduce the
13   *    above copyright notice, this list of conditions and the
14   *    following disclaimer in the documentation and/or other
15   *    materials provided with the distribution.
16   *
17   * 3. The name "JDBM" must not be used to endorse or promote
18   *    products derived from this Software without prior written
19   *    permission of Cees de Groot.  For written permission,
20   *    please contact cg@cdegroot.com.
21   *
22   * 4. Products derived from this Software may not be called "JDBM"
23   *    nor may "JDBM" appear in their names without prior written
24   *    permission of Cees de Groot. 
25   *
26   * 5. Due credit should be given to the JDBM Project
27   *    (http://jdbm.sourceforge.net/).
28   *
29   * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
30   * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
31   * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
32   * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
33   * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
34   * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
35   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
36   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
38   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
39   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
40   * OF THE POSSIBILITY OF SUCH DAMAGE.
41   *
42   * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
43   * Contributions are Copyright (C) 2000 by their associated contributors.
44   *
45   * $Id: RecordHeader.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
46   */
47  
48  package jdbm.recman;
49  
50  /**
51   *  The data that comes at the start of a record of data. It stores 
52   *  both the current size and the avaliable size for the record - the latter
53   *  can be bigger than the former, which allows the record to grow without
54   *  needing to be moved and which allows the system to put small records
55   *  in larger free spots.
56   */
57  class RecordHeader {
58      // offsets
59      private static final short O_CURRENTSIZE = 0; // int currentSize
60      private static final short O_AVAILABLESIZE = Magic.SZ_INT; // int availableSize
61      static final int SIZE = O_AVAILABLESIZE + Magic.SZ_INT;
62      
63      // my block and the position within the block
64      private BlockIo block;
65      private short pos;
66  
67      /**
68       *  Constructs a record header from the indicated data starting at
69       *  the indicated position.
70       */
71      RecordHeader(BlockIo block, short pos) {
72          this.block = block;
73          this.pos = pos;
74          if (pos > (RecordFile.BLOCK_SIZE - SIZE))
75              throw new Error("Offset too large for record header (" 
76                              + block.getBlockId() + ":" 
77                              + pos + ")");
78      }
79  
80      /** Returns the current size */
81      int getCurrentSize() {
82          return block.readInt(pos + O_CURRENTSIZE);
83      }
84      
85      /** Sets the current size */
86      void setCurrentSize(int value) {
87          block.writeInt(pos + O_CURRENTSIZE, value);
88      }
89      
90      /** Returns the available size */
91      int getAvailableSize() {
92          return block.readInt(pos + O_AVAILABLESIZE);
93      }
94      
95      /** Sets the available size */
96      void setAvailableSize(int value) {
97          block.writeInt(pos + O_AVAILABLESIZE, value);
98      }
99  
100     // overrides java.lang.Object
101     public String toString() {
102         return "RH(" + block.getBlockId() + ":" + pos 
103             + ", avl=" + getAvailableSize()
104             + ", cur=" + getCurrentSize() 
105             + ")";
106     }
107 }