1 /*-
2  * Copyright (c) 1990, 1993, 1994
3  *  The Regents of the University of California.  All rights reserved.
4  *
5  * This code is derived from software contributed to Berkeley by
6  * Margo Seltzer.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. ***REMOVED*** - see
17  *    ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change
18  * 4. Neither the name of the University nor the names of its contributors
19  *    may be used to endorse or promote products derived from this software
20  *    without specific prior written permission.
21  *
22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32  * SUCH DAMAGE.
33  *
34  *  @(#)page.h  8.2 (Berkeley) 5/31/94
35  */
36 
37 /*
38  * Definitions for hashing page file format.
39  */
40 
41 /*
42  * routines dealing with a data page
43  *
44  * page format:
45  *  +------------------------------+
46  * p    | n | keyoff | datoff | keyoff |
47  *  +------------+--------+--------+
48  *  | datoff | free  |  ptr  | --> |
49  *  +--------+---------------------+
50  *  |    F R E E A R E A           |
51  *  +--------------+---------------+
52  *  |  <---- - - - | data          |
53  *  +--------+-----+----+----------+
54  *  |  key   | data     | key      |
55  *  +--------+----------+----------+
56  *
57  * Pointer to the free space is always:  p[p[0] + 2]
58  * Amount of free space on the page is:  p[p[0] + 1]
59  */
60 
61 /*
62  * How many bytes required for this pair?
63  *  2 shorts in the table at the top of the page + room for the
64  *  key and room for the data
65  *
66  * We prohibit entering a pair on a page unless there is also room to append
67  * an overflow page. The reason for this it that you can get in a situation
68  * where a single key/data pair fits on a page, but you can't append an
69  * overflow page and later you'd have to split the key/data and handle like
70  * a big pair.
71  * You might as well do this up front.
72  */
73 #ifndef PAGE_H
74 #define PAGE_H
75 
76 #define PAIRSIZE(K, D) (2 * sizeof(uint16) + (K)->size + (D)->size)
77 #define BIGOVERHEAD (4 * sizeof(uint16))
78 #define KEYSIZE(K) (4 * sizeof(uint16) + (K)->size);
79 #define OVFLSIZE (2 * sizeof(uint16))
80 #define FREESPACE(P) ((P)[(P)[0] + 1])
81 #define OFFSET(P) ((P)[(P)[0] + 2])
82 #define PAIRFITS(P, K, D)    \
83     (((P)[2] >= REAL_KEY) && \
84      (PAIRSIZE((K), (D)) + OVFLSIZE) <= FREESPACE((P)))
85 #define PAGE_META(N) (((N) + 3) * sizeof(uint16))
86 
87 typedef struct {
88     BUFHEAD *newp;
89     BUFHEAD *oldp;
90     BUFHEAD *nextp;
91     uint16 next_addr;
92 } SPLIT_RETURN;
93 #endif
94