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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: TranslationPage.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
46   */
47  
48  package jdbm.recman;
49  
50  /**
51   *  Class describing a page that holds translations from physical rowids
52   *  to logical rowids. In fact, the page just holds physical rowids - the
53   *  page's block is the block for the logical rowid, the offset serve
54   *  as offset for the rowids.
55   */
56  final class TranslationPage extends PageHeader {
57      // offsets
58      static final short O_TRANS = PageHeader.SIZE; // short count
59      static final short ELEMS_PER_PAGE = 
60          (RecordFile.BLOCK_SIZE - O_TRANS) / PhysicalRowId.SIZE;
61      
62      // slots we returned.
63      final PhysicalRowId[] slots = new PhysicalRowId[ELEMS_PER_PAGE];
64  
65      /**
66       *  Constructs a data page view from the indicated block.
67       */
68      TranslationPage(BlockIo block) {
69          super(block);
70      }
71  
72      /**
73       *  Factory method to create or return a data page for the
74       *  indicated block.
75       */
76      static TranslationPage getTranslationPageView(BlockIo block) {
77          BlockView view = block.getView();
78          if (view != null && view instanceof TranslationPage)
79              return (TranslationPage) view;
80          else
81              return new TranslationPage(block);
82      }
83  
84      /** Returns the value of the indicated rowid on the page */
85      PhysicalRowId get(short offset) {
86          int slot = (offset - O_TRANS) / PhysicalRowId.SIZE;
87          if (slots[slot] == null) 
88              slots[slot] = new PhysicalRowId(block, offset);
89          return slots[slot];
90      }
91  }