[apple/libc.git] / db / hash / hash.h

/*
 * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* Operations */
typedef enum {
	HASH_GET, HASH_PUT, HASH_PUTNEW, HASH_DELETE, HASH_FIRST, HASH_NEXT
} ACTION;

/* Buffer Management structures */
typedef struct _bufhead BUFHEAD;

struct _bufhead {
	BUFHEAD	*prev;		/* LRU links */
	BUFHEAD	*next;		/* LRU links */
	BUFHEAD	*ovfl;		/* Overflow page buffer header */
	u_int	 addr;		/* Address of this page */
	char	*page;		/* Actual page data */
	char	 flags;
#define	BUF_MOD		0x0001
#define BUF_DISK	0x0002
#define	BUF_BUCKET	0x0004
#define	BUF_PIN		0x0008
};

#define IS_BUCKET(X)	((X) & BUF_BUCKET)

typedef BUFHEAD **SEGMENT;

/* Hash Table Information */
typedef struct hashhdr {	/* Disk resident portion */
	int	magic;		/* Magic NO for hash tables */
	int	version;	/* Version ID */
	long	lorder;		/* Byte Order */
	int	bsize;		/* Bucket/Page Size */
	int	bshift;		/* Bucket shift */
	int	dsize;		/* Directory Size */
	int	ssize;		/* Segment Size */
	int	sshift;		/* Segment shift */
	int	ovfl_point;	/* Where overflow pages are being allocated */
	int	last_freed;	/* Last overflow page freed */
	int	max_bucket;	/* ID of Maximum bucket in use */
	int	high_mask;	/* Mask to modulo into entire table */
	int	low_mask;	/* Mask to modulo into lower half of table */
	int	ffactor;	/* Fill factor */
	int	nkeys;		/* Number of keys in hash table */
	int	hdrpages;	/* Size of table header */
	int	h_charkey;	/* value of hash(CHARKEY) */
#define NCACHED	32		/* number of bit maps and spare points */
	int	spares[NCACHED];/* spare pages for overflow */
	u_short	bitmaps[NCACHED];	/* address of overflow page bitmaps */
} HASHHDR;

typedef struct htab {		/* Memory resident data structure */
	HASHHDR hdr;		/* Header */
	int	nsegs;		/* Number of allocated segments */
	int	exsegs;		/* Number of extra allocated segments */
	u_int32_t		/* Hash function */
	    (*hash)__P((const void *, size_t));
	int	flags;		/* Flag values */
	int	fp;		/* File pointer */
	char	*tmp_buf;	/* Temporary Buffer for BIG data */
	char	*tmp_key;	/* Temporary Buffer for BIG keys */
	BUFHEAD *cpage;		/* Current page */
	int	cbucket;	/* Current bucket */
	int	cndx;		/* Index of next item on cpage */
	int	error;		/* Error Number -- for DBM compatability */
	int	new_file;	/* Indicates if fd is backing store or no */
	int	save_file;	/* Indicates whether we need to flush file at
				 * exit */
	u_long *mapp[NCACHED];	/* Pointers to page maps */
	int	nmaps;		/* Initial number of bitmaps */
	int	nbufs;		/* Number of buffers left to allocate */
	BUFHEAD bufhead;	/* Header of buffer lru list */
	SEGMENT *dir;		/* Hash Bucket directory */
} HTAB;

/*
 * Constants
 */
#define	MAX_BSIZE		65536		/* 2^16 */
#define MIN_BUFFERS		6
#define MINHDRSIZE		512
#define DEF_BUFSIZE		65536		/* 64 K */
#define DEF_BUCKET_SIZE		4096
#define DEF_BUCKET_SHIFT	12		/* log2(BUCKET) */
#define DEF_SEGSIZE		256
#define DEF_SEGSIZE_SHIFT	8		/* log2(SEGSIZE)	 */
#define DEF_DIRSIZE		256
#define DEF_FFACTOR		65536
#define MIN_FFACTOR		4
#define SPLTMAX			8
#define CHARKEY			"%$sniglet^&"
#define NUMKEY			1038583
#define BYTE_SHIFT		3
#define INT_TO_BYTE		2
#define INT_BYTE_SHIFT		5
#define ALL_SET			((u_int)0xFFFFFFFF)
#define ALL_CLEAR		0

#define PTROF(X)	((BUFHEAD *)((u_int)(X)&~0x3))
#define ISMOD(X)	((u_int)(X)&0x1)
#define DOMOD(X)	((X) = (char *)((u_int)(X)|0x1))
#define ISDISK(X)	((u_int)(X)&0x2)
#define DODISK(X)	((X) = (char *)((u_int)(X)|0x2))

#define BITS_PER_MAP	32

/* Given the address of the beginning of a big map, clear/set the nth bit */
#define CLRBIT(A, N)	((A)[(N)/BITS_PER_MAP] &= ~(1<<((N)%BITS_PER_MAP)))
#define SETBIT(A, N)	((A)[(N)/BITS_PER_MAP] |= (1<<((N)%BITS_PER_MAP)))
#define ISSET(A, N)	((A)[(N)/BITS_PER_MAP] & (1<<((N)%BITS_PER_MAP)))

/* Overflow management */
/*
 * Overflow page numbers are allocated per split point.  At each doubling of
 * the table, we can allocate extra pages.  So, an overflow page number has
 * the top 5 bits indicate which split point and the lower 11 bits indicate
 * which page at that split point is indicated (pages within split points are
 * numberered starting with 1).
 */

#define SPLITSHIFT	11
#define SPLITMASK	0x7FF
#define SPLITNUM(N)	(((u_int)(N)) >> SPLITSHIFT)
#define OPAGENUM(N)	((N) & SPLITMASK)
#define	OADDR_OF(S,O)	((u_int)((u_int)(S) << SPLITSHIFT) + (O))

#define BUCKET_TO_PAGE(B) \
	(B) + hashp->HDRPAGES + ((B) ? hashp->SPARES[__log2((B)+1)-1] : 0)
#define OADDR_TO_PAGE(B) 	\
	BUCKET_TO_PAGE ( (1 << SPLITNUM((B))) -1 ) + OPAGENUM((B));

/*
 * page.h contains a detailed description of the page format.
 *
 * Normally, keys and data are accessed from offset tables in the top of
 * each page which point to the beginning of the key and data.  There are
 * four flag values which may be stored in these offset tables which indicate
 * the following:
 *
 *
 * OVFLPAGE	Rather than a key data pair, this pair contains
 *		the address of an overflow page.  The format of
 *		the pair is:
 *		    OVERFLOW_PAGE_NUMBER OVFLPAGE
 *
 * PARTIAL_KEY	This must be the first key/data pair on a page
 *		and implies that page contains only a partial key.
 *		That is, the key is too big to fit on a single page
 *		so it starts on this page and continues on the next.
 *		The format of the page is:
 *		    KEY_OFF PARTIAL_KEY OVFL_PAGENO OVFLPAGE
 *		
 *		    KEY_OFF -- offset of the beginning of the key
 *		    PARTIAL_KEY -- 1
 *		    OVFL_PAGENO - page number of the next overflow page
 *		    OVFLPAGE -- 0
 *
 * FULL_KEY	This must be the first key/data pair on the page.  It
 *		is used in two cases.
 *
 *		Case 1:
 *		    There is a complete key on the page but no data
 *		    (because it wouldn't fit).  The next page contains
 *		    the data.
 *
 *		    Page format it:
 *		    KEY_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
 *
 *		    KEY_OFF -- offset of the beginning of the key
 *		    FULL_KEY -- 2
 *		    OVFL_PAGENO - page number of the next overflow page
 *		    OVFLPAGE -- 0
 *
 *		Case 2:
 *		    This page contains no key, but part of a large
 *		    data field, which is continued on the next page.
 *
 *		    Page format it:
 *		    DATA_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
 *
 *		    KEY_OFF -- offset of the beginning of the data on
 *				this page
 *		    FULL_KEY -- 2
 *		    OVFL_PAGENO - page number of the next overflow page
 *		    OVFLPAGE -- 0
 *
 * FULL_KEY_DATA 
 *		This must be the first key/data pair on the page.
 *		There are two cases:
 *
 *		Case 1:
 *		    This page contains a key and the beginning of the
 *		    data field, but the data field is continued on the
 *		    next page.
 *
 *		    Page format is:
 *		    KEY_OFF FULL_KEY_DATA OVFL_PAGENO DATA_OFF
 *
 *		    KEY_OFF -- offset of the beginning of the key
 *		    FULL_KEY_DATA -- 3
 *		    OVFL_PAGENO - page number of the next overflow page
 *		    DATA_OFF -- offset of the beginning of the data
 *
 *		Case 2:
 *		    This page contains the last page of a big data pair.
 *		    There is no key, only the  tail end of the data
 *		    on this page.
 *
 *		    Page format is:
 *		    DATA_OFF FULL_KEY_DATA <OVFL_PAGENO> <OVFLPAGE>
 *
 *		    DATA_OFF -- offset of the beginning of the data on
 *				this page
 *		    FULL_KEY_DATA -- 3
 *		    OVFL_PAGENO - page number of the next overflow page
 *		    OVFLPAGE -- 0
 *
 *		    OVFL_PAGENO and OVFLPAGE are optional (they are
 *		    not present if there is no next page).
 */

#define OVFLPAGE	0
#define PARTIAL_KEY	1
#define FULL_KEY	2
#define FULL_KEY_DATA	3
#define	REAL_KEY	4

/* Short hands for accessing structure */
#define BSIZE		hdr.bsize
#define BSHIFT		hdr.bshift
#define DSIZE		hdr.dsize
#define SGSIZE		hdr.ssize
#define SSHIFT		hdr.sshift
#define LORDER		hdr.lorder
#define OVFL_POINT	hdr.ovfl_point
#define	LAST_FREED	hdr.last_freed
#define MAX_BUCKET	hdr.max_bucket
#define FFACTOR		hdr.ffactor
#define HIGH_MASK	hdr.high_mask
#define LOW_MASK	hdr.low_mask
#define NKEYS		hdr.nkeys
#define HDRPAGES	hdr.hdrpages
#define SPARES		hdr.spares
#define BITMAPS		hdr.bitmaps
#define VERSION		hdr.version
#define MAGIC		hdr.magic
#define NEXT_FREE	hdr.next_free
#define H_CHARKEY	hdr.h_charkey
Commit	Line	Data
e9ce8d39 A	1	/*
	2	* Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
	3	*
	4	* @APPLE_LICENSE_HEADER_START@
	5	*
734aad71	6	* Copyright (c) 1999-2003 Apple Computer, Inc. All Rights Reserved.
e9ce8d39	7	*
734aad71 A	8	* This file contains Original Code and/or Modifications of Original Code
	9	* as defined in and that are subject to the Apple Public Source License
	10	* Version 2.0 (the 'License'). You may not use this file except in
	11	* compliance with the License. Please obtain a copy of the License at
	12	* http://www.opensource.apple.com/apsl/ and read it before using this
	13	* file.
	14	*
	15	* The Original Code and all software distributed under the License are
	16	* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
e9ce8d39 A	17	* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
e9ce8d39 A	18	* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
734aad71 A	19	* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
	20	* Please see the License for the specific language governing rights and
	21	* limitations under the License.
e9ce8d39 A	22	*
	23	* @APPLE_LICENSE_HEADER_END@
	24	*/
	25	/*
	26	* Copyright (c) 1990, 1993
	27	* The Regents of the University of California. All rights reserved.
	28	*
	29	* This code is derived from software contributed to Berkeley by
	30	* Margo Seltzer.
	31	*
	32	* Redistribution and use in source and binary forms, with or without
	33	* modification, are permitted provided that the following conditions
	34	* are met:
	35	* 1. Redistributions of source code must retain the above copyright
	36	* notice, this list of conditions and the following disclaimer.
	37	* 2. Redistributions in binary form must reproduce the above copyright
	38	* notice, this list of conditions and the following disclaimer in the
	39	* documentation and/or other materials provided with the distribution.
	40	* 3. All advertising materials mentioning features or use of this software
	41	* must display the following acknowledgement:
	42	* This product includes software developed by the University of
	43	* California, Berkeley and its contributors.
	44	* 4. Neither the name of the University nor the names of its contributors
	45	* may be used to endorse or promote products derived from this software
	46	* without specific prior written permission.
	47	*
	48	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	49	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	50	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	51	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	52	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	53	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	54	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	55	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	56	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	57	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	58	* SUCH DAMAGE.
	59	*/
	60
	61	/* Operations */
	62	typedef enum {
	63	HASH_GET, HASH_PUT, HASH_PUTNEW, HASH_DELETE, HASH_FIRST, HASH_NEXT
	64	} ACTION;
	65
	66	/* Buffer Management structures */
	67	typedef struct _bufhead BUFHEAD;
	68
	69	struct _bufhead {
	70	BUFHEAD prev; / LRU links */
	71	BUFHEAD next; / LRU links */
	72	BUFHEAD ovfl; / Overflow page buffer header */
	73	u_int addr; /* Address of this page */
	74	char page; / Actual page data */
	75	char flags;
	76	#define BUF_MOD 0x0001
	77	#define BUF_DISK 0x0002
	78	#define BUF_BUCKET 0x0004
	79	#define BUF_PIN 0x0008
	80	};
	81
	82	#define IS_BUCKET(X) ((X) & BUF_BUCKET)
	83
	84	typedef BUFHEAD **SEGMENT;
	85
86	/* Hash Table Information */
87	typedef struct hashhdr { /* Disk resident portion */
88	int magic; /* Magic NO for hash tables */
89	int version; /* Version ID */
90	long lorder; /* Byte Order */
91	int bsize; /* Bucket/Page Size */
92	int bshift; /* Bucket shift */
93	int dsize; /* Directory Size */
94	int ssize; /* Segment Size */
95	int sshift; /* Segment shift */
96	int ovfl_point; /* Where overflow pages are being allocated */
97	int last_freed; /* Last overflow page freed */
98	int max_bucket; /* ID of Maximum bucket in use */
99	int high_mask; /* Mask to modulo into entire table */
100	int low_mask; /* Mask to modulo into lower half of table */
101	int ffactor; /* Fill factor */
102	int nkeys; /* Number of keys in hash table */
103	int hdrpages; /* Size of table header */
104	int h_charkey; /* value of hash(CHARKEY) */
105	#define NCACHED 32 /* number of bit maps and spare points */
106	int spares[NCACHED];/* spare pages for overflow */
107	u_short bitmaps[NCACHED]; /* address of overflow page bitmaps */
108	} HASHHDR;
109
110	typedef struct htab { /* Memory resident data structure */
111	HASHHDR hdr; /* Header */
112	int nsegs; /* Number of allocated segments */
113	int exsegs; /* Number of extra allocated segments */
114	u_int32_t /* Hash function */
115	(hash)__P((const void , size_t));
116	int flags; /* Flag values */
117	int fp; /* File pointer */
118	char tmp_buf; / Temporary Buffer for BIG data */
119	char tmp_key; / Temporary Buffer for BIG keys */
120	BUFHEAD cpage; / Current page */
121	int cbucket; /* Current bucket */
122	int cndx; /* Index of next item on cpage */
123	int error; /* Error Number -- for DBM compatability */
124	int new_file; /* Indicates if fd is backing store or no */
125	int save_file; /* Indicates whether we need to flush file at
126	* exit */
127	u_long mapp[NCACHED]; / Pointers to page maps */
128	int nmaps; /* Initial number of bitmaps */
129	int nbufs; /* Number of buffers left to allocate */
130	BUFHEAD bufhead; /* Header of buffer lru list */
131	SEGMENT dir; / Hash Bucket directory */
132	} HTAB;
133
134	/*
135	* Constants
136	*/
137	#define MAX_BSIZE 65536 /* 2^16 */
138	#define MIN_BUFFERS 6
139	#define MINHDRSIZE 512
140	#define DEF_BUFSIZE 65536 /* 64 K */
141	#define DEF_BUCKET_SIZE 4096
142	#define DEF_BUCKET_SHIFT 12 /* log2(BUCKET) */
143	#define DEF_SEGSIZE 256
144	#define DEF_SEGSIZE_SHIFT 8 /* log2(SEGSIZE) */
145	#define DEF_DIRSIZE 256
146	#define DEF_FFACTOR 65536
147	#define MIN_FFACTOR 4
148	#define SPLTMAX 8
149	#define CHARKEY "%$sniglet^&"
150	#define NUMKEY 1038583
151	#define BYTE_SHIFT 3
152	#define INT_TO_BYTE 2
153	#define INT_BYTE_SHIFT 5
154	#define ALL_SET ((u_int)0xFFFFFFFF)
155	#define ALL_CLEAR 0
156
157	#define PTROF(X) ((BUFHEAD *)((u_int)(X)&~0x3))
158	#define ISMOD(X) ((u_int)(X)&0x1)
159	#define DOMOD(X) ((X) = (char *)((u_int)(X)\|0x1))
160	#define ISDISK(X) ((u_int)(X)&0x2)
161	#define DODISK(X) ((X) = (char *)((u_int)(X)\|0x2))
162
163	#define BITS_PER_MAP 32
164
165	/* Given the address of the beginning of a big map, clear/set the nth bit */
166	#define CLRBIT(A, N) ((A)[(N)/BITS_PER_MAP] &= ~(1<<((N)%BITS_PER_MAP)))
167	#define SETBIT(A, N) ((A)[(N)/BITS_PER_MAP] \|= (1<<((N)%BITS_PER_MAP)))
168	#define ISSET(A, N) ((A)[(N)/BITS_PER_MAP] & (1<<((N)%BITS_PER_MAP)))
169
170	/* Overflow management */
171	/*
172	* Overflow page numbers are allocated per split point. At each doubling of
173	* the table, we can allocate extra pages. So, an overflow page number has
174	* the top 5 bits indicate which split point and the lower 11 bits indicate
175	* which page at that split point is indicated (pages within split points are
176	* numberered starting with 1).
177	*/
178
179	#define SPLITSHIFT 11
180	#define SPLITMASK 0x7FF
181	#define SPLITNUM(N) (((u_int)(N)) >> SPLITSHIFT)
182	#define OPAGENUM(N) ((N) & SPLITMASK)
183	#define OADDR_OF(S,O) ((u_int)((u_int)(S) << SPLITSHIFT) + (O))
184
185	#define BUCKET_TO_PAGE(B) \
186	(B) + hashp->HDRPAGES + ((B) ? hashp->SPARES[__log2((B)+1)-1] : 0)
187	#define OADDR_TO_PAGE(B) \
188	BUCKET_TO_PAGE ( (1 << SPLITNUM((B))) -1 ) + OPAGENUM((B));
189
190	/*
191	* page.h contains a detailed description of the page format.
192	*
193	* Normally, keys and data are accessed from offset tables in the top of
194	* each page which point to the beginning of the key and data. There are
195	* four flag values which may be stored in these offset tables which indicate
196	* the following:
197	*
198	*
199	* OVFLPAGE Rather than a key data pair, this pair contains
200	* the address of an overflow page. The format of
201	* the pair is:
202	* OVERFLOW_PAGE_NUMBER OVFLPAGE
203	*
204	* PARTIAL_KEY This must be the first key/data pair on a page
205	* and implies that page contains only a partial key.
206	* That is, the key is too big to fit on a single page
207	* so it starts on this page and continues on the next.
208	* The format of the page is:
209	* KEY_OFF PARTIAL_KEY OVFL_PAGENO OVFLPAGE
210	*
211	* KEY_OFF -- offset of the beginning of the key
212	* PARTIAL_KEY -- 1
213	* OVFL_PAGENO - page number of the next overflow page
214	* OVFLPAGE -- 0
215	*
216	* FULL_KEY This must be the first key/data pair on the page. It
217	* is used in two cases.
218	*
219	* Case 1:
220	* There is a complete key on the page but no data
221	* (because it wouldn't fit). The next page contains
222	* the data.
223	*
224	* Page format it:
225	* KEY_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
226	*
227	* KEY_OFF -- offset of the beginning of the key
228	* FULL_KEY -- 2
229	* OVFL_PAGENO - page number of the next overflow page
230	* OVFLPAGE -- 0
231	*
232	* Case 2:
233	* This page contains no key, but part of a large
234	* data field, which is continued on the next page.
235	*
236	* Page format it:
237	* DATA_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
238	*
239	* KEY_OFF -- offset of the beginning of the data on
240	* this page
241	* FULL_KEY -- 2
242	* OVFL_PAGENO - page number of the next overflow page
243	* OVFLPAGE -- 0
244	*
245	* FULL_KEY_DATA
246	* This must be the first key/data pair on the page.
247	* There are two cases:
248	*
249	* Case 1:
250	* This page contains a key and the beginning of the
251	* data field, but the data field is continued on the
252	* next page.
253	*
254	* Page format is:
255	* KEY_OFF FULL_KEY_DATA OVFL_PAGENO DATA_OFF
256	*
257	* KEY_OFF -- offset of the beginning of the key
258	* FULL_KEY_DATA -- 3
259	* OVFL_PAGENO - page number of the next overflow page
260	* DATA_OFF -- offset of the beginning of the data
261	*
262	* Case 2:
263	* This page contains the last page of a big data pair.
264	* There is no key, only the tail end of the data
265	* on this page.
266	*
267	* Page format is:
268	* DATA_OFF FULL_KEY_DATA <OVFL_PAGENO> <OVFLPAGE>
269	*
270	* DATA_OFF -- offset of the beginning of the data on
271	* this page
272	* FULL_KEY_DATA -- 3
273	* OVFL_PAGENO - page number of the next overflow page
274	* OVFLPAGE -- 0
275	*
276	* OVFL_PAGENO and OVFLPAGE are optional (they are
277	* not present if there is no next page).
278	*/
279
280	#define OVFLPAGE 0
281	#define PARTIAL_KEY 1
282	#define FULL_KEY 2
283	#define FULL_KEY_DATA 3
284	#define REAL_KEY 4
285
286	/* Short hands for accessing structure */
287	#define BSIZE hdr.bsize
288	#define BSHIFT hdr.bshift
289	#define DSIZE hdr.dsize
290	#define SGSIZE hdr.ssize
291	#define SSHIFT hdr.sshift
292	#define LORDER hdr.lorder
293	#define OVFL_POINT hdr.ovfl_point
294	#define LAST_FREED hdr.last_freed
295	#define MAX_BUCKET hdr.max_bucket
296	#define FFACTOR hdr.ffactor
297	#define HIGH_MASK hdr.high_mask
298	#define LOW_MASK hdr.low_mask
299	#define NKEYS hdr.nkeys
300	#define HDRPAGES hdr.hdrpages
301	#define SPARES hdr.spares
302	#define BITMAPS hdr.bitmaps
303	#define VERSION hdr.version
304	#define MAGIC hdr.magic
305	#define NEXT_FREE hdr.next_free
306	#define H_CHARKEY hdr.h_charkey