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

/*-
 * Copyright (c) 1990, 1993, 1994
 *	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.
 *
 *	@(#)hash.h	8.3 (Berkeley) 5/31/94
 * $FreeBSD: src/lib/libc/db/hash/hash.h,v 1.6 2002/03/21 22:46:26 obrien Exp $
 */

/* 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_int32_t	 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 */
	u_int32_t	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_int16_t	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)(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 
					 * compatibility */
	int		new_file;	/* Indicates if fd is backing store 
					 * or no */
	int		save_file;	/* Indicates whether we need to flush 
					 * file at
					 * exit */
	u_int32_t	*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 */
					/* other flags */
	int		nextkey_eof :1;	/* dbm_nextkey() reached EOF */
} 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_int32_t)0xFFFFFFFF)
#define ALL_CLEAR		0

#define PTROF(X)	((BUFHEAD *)((ptrdiff_t)(X)&~0x3))
#define ISMOD(X)	((u_int32_t)(ptrdiff_t)(X)&0x1)
#define DOMOD(X)	((X) = (char *)((ptrdiff_t)(X)|0x1))
#define ISDISK(X)	((u_int32_t)(ptrdiff_t)(X)&0x2)
#define DODISK(X)	((X) = (char *)((ptrdiff_t)(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_int32_t)(N)) >> SPLITSHIFT)
#define OPAGENUM(N)	((N) & SPLITMASK)
#define	OADDR_OF(S,O)	((u_int32_t)((u_int32_t)(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
224c7076 A	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. All advertising materials mentioning features or use of this software
	17	* must display the following acknowledgement:
	18	* This product includes software developed by the University of
	19	* California, Berkeley and its contributors.
	20	* 4. Neither the name of the University nor the names of its contributors
	21	* may be used to endorse or promote products derived from this software
	22	* without specific prior written permission.
	23	*
	24	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	25	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	26	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	27	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	28	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	29	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	30	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	31	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	32	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	33	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	34	* SUCH DAMAGE.
	35	*
	36	* @(#)hash.h 8.3 (Berkeley) 5/31/94
	37	* $FreeBSD: src/lib/libc/db/hash/hash.h,v 1.6 2002/03/21 22:46:26 obrien Exp $
	38	*/
	39
	40	/* Operations */
	41	typedef enum {
	42	HASH_GET, HASH_PUT, HASH_PUTNEW, HASH_DELETE, HASH_FIRST, HASH_NEXT
	43	} ACTION;
	44
	45	/* Buffer Management structures */
	46	typedef struct _bufhead BUFHEAD;
	47
	48	struct _bufhead {
	49	BUFHEAD prev; / LRU links */
	50	BUFHEAD next; / LRU links */
	51	BUFHEAD ovfl; / Overflow page buffer header */
	52	u_int32_t addr; /* Address of this page */
	53	char page; / Actual page data */
	54	char flags;
	55	#define BUF_MOD 0x0001
	56	#define BUF_DISK 0x0002
	57	#define BUF_BUCKET 0x0004
	58	#define BUF_PIN 0x0008
	59	};
	60
	61	#define IS_BUCKET(X) ((X) & BUF_BUCKET)
	62
	63	typedef BUFHEAD **SEGMENT;
	64
65	/* Hash Table Information */
66	typedef struct hashhdr { /* Disk resident portion */
67	int magic; /* Magic NO for hash tables */
68	int version; /* Version ID */
69	u_int32_t lorder; /* Byte Order */
70	int bsize; /* Bucket/Page Size */
71	int bshift; /* Bucket shift */
72	int dsize; /* Directory Size */
73	int ssize; /* Segment Size */
74	int sshift; /* Segment shift */
75	int ovfl_point; /* Where overflow pages are being
76	* allocated */
77	int last_freed; /* Last overflow page freed */
78	int max_bucket; /* ID of Maximum bucket in use */
79	int high_mask; /* Mask to modulo into entire table */
80	int low_mask; /* Mask to modulo into lower half of
81	* table */
82	int ffactor; /* Fill factor */
83	int nkeys; /* Number of keys in hash table */
84	int hdrpages; /* Size of table header */
85	int h_charkey; /* value of hash(CHARKEY) */
86	#define NCACHED 32 /* number of bit maps and spare
87	* points */
88	int spares[NCACHED];/* spare pages for overflow */
89	u_int16_t bitmaps[NCACHED]; /* address of overflow page
90	* bitmaps */
91	} HASHHDR;
92
93	typedef struct htab { /* Memory resident data structure */
94	HASHHDR hdr; /* Header */
95	int nsegs; /* Number of allocated segments */
96	int exsegs; /* Number of extra allocated
97	* segments */
98	u_int32_t /* Hash function */
99	(hash)(const void , size_t);
100	int flags; /* Flag values */
101	int fp; /* File pointer */
102	char tmp_buf; / Temporary Buffer for BIG data */
103	char tmp_key; / Temporary Buffer for BIG keys */
104	BUFHEAD cpage; / Current page */
105	int cbucket; /* Current bucket */
106	int cndx; /* Index of next item on cpage */
107	int error; /* Error Number -- for DBM
108	* compatibility */
109	int new_file; /* Indicates if fd is backing store
110	* or no */
111	int save_file; /* Indicates whether we need to flush
112	* file at
113	* exit */
114	u_int32_t mapp[NCACHED]; / Pointers to page maps */
115	int nmaps; /* Initial number of bitmaps */
116	int nbufs; /* Number of buffers left to
117	* allocate */
118	BUFHEAD bufhead; /* Header of buffer lru list */
119	SEGMENT dir; / Hash Bucket directory */
120	/* other flags */
121	int nextkey_eof :1; /* dbm_nextkey() reached EOF */
122	} HTAB;
123
124	/*
125	* Constants
126	*/
127	#define MAX_BSIZE 65536 /* 2^16 */
128	#define MIN_BUFFERS 6
129	#define MINHDRSIZE 512
130	#define DEF_BUFSIZE 65536 /* 64 K */
131	#define DEF_BUCKET_SIZE 4096
132	#define DEF_BUCKET_SHIFT 12 /* log2(BUCKET) */
133	#define DEF_SEGSIZE 256
134	#define DEF_SEGSIZE_SHIFT 8 /* log2(SEGSIZE) */
135	#define DEF_DIRSIZE 256
136	#define DEF_FFACTOR 65536
137	#define MIN_FFACTOR 4
138	#define SPLTMAX 8
139	#define CHARKEY "%$sniglet^&"
140	#define NUMKEY 1038583
141	#define BYTE_SHIFT 3
142	#define INT_TO_BYTE 2
143	#define INT_BYTE_SHIFT 5
144	#define ALL_SET ((u_int32_t)0xFFFFFFFF)
145	#define ALL_CLEAR 0
146
147	#define PTROF(X) ((BUFHEAD *)((ptrdiff_t)(X)&~0x3))
148	#define ISMOD(X) ((u_int32_t)(ptrdiff_t)(X)&0x1)
149	#define DOMOD(X) ((X) = (char *)((ptrdiff_t)(X)\|0x1))
150	#define ISDISK(X) ((u_int32_t)(ptrdiff_t)(X)&0x2)
151	#define DODISK(X) ((X) = (char *)((ptrdiff_t)(X)\|0x2))
152
153	#define BITS_PER_MAP 32
154
155	/* Given the address of the beginning of a big map, clear/set the nth bit */
156	#define CLRBIT(A, N) ((A)[(N)/BITS_PER_MAP] &= ~(1<<((N)%BITS_PER_MAP)))
157	#define SETBIT(A, N) ((A)[(N)/BITS_PER_MAP] \|= (1<<((N)%BITS_PER_MAP)))
158	#define ISSET(A, N) ((A)[(N)/BITS_PER_MAP] & (1<<((N)%BITS_PER_MAP)))
159
160	/* Overflow management */
161	/*
162	* Overflow page numbers are allocated per split point. At each doubling of
163	* the table, we can allocate extra pages. So, an overflow page number has
164	* the top 5 bits indicate which split point and the lower 11 bits indicate
165	* which page at that split point is indicated (pages within split points are
166	* numberered starting with 1).
167	*/
168
169	#define SPLITSHIFT 11
170	#define SPLITMASK 0x7FF
171	#define SPLITNUM(N) (((u_int32_t)(N)) >> SPLITSHIFT)
172	#define OPAGENUM(N) ((N) & SPLITMASK)
173	#define OADDR_OF(S,O) ((u_int32_t)((u_int32_t)(S) << SPLITSHIFT) + (O))
174
175	#define BUCKET_TO_PAGE(B) \
176	(B) + hashp->HDRPAGES + ((B) ? hashp->SPARES[__log2((B)+1)-1] : 0)
177	#define OADDR_TO_PAGE(B) \
178	BUCKET_TO_PAGE ( (1 << SPLITNUM((B))) -1 ) + OPAGENUM((B));
179
180	/*
181	* page.h contains a detailed description of the page format.
182	*
183	* Normally, keys and data are accessed from offset tables in the top of
184	* each page which point to the beginning of the key and data. There are
185	* four flag values which may be stored in these offset tables which indicate
186	* the following:
187	*
188	*
189	* OVFLPAGE Rather than a key data pair, this pair contains
190	* the address of an overflow page. The format of
191	* the pair is:
192	* OVERFLOW_PAGE_NUMBER OVFLPAGE
193	*
194	* PARTIAL_KEY This must be the first key/data pair on a page
195	* and implies that page contains only a partial key.
196	* That is, the key is too big to fit on a single page
197	* so it starts on this page and continues on the next.
198	* The format of the page is:
199	* KEY_OFF PARTIAL_KEY OVFL_PAGENO OVFLPAGE
200	*
201	* KEY_OFF -- offset of the beginning of the key
202	* PARTIAL_KEY -- 1
203	* OVFL_PAGENO - page number of the next overflow page
204	* OVFLPAGE -- 0
205	*
206	* FULL_KEY This must be the first key/data pair on the page. It
207	* is used in two cases.
208	*
209	* Case 1:
210	* There is a complete key on the page but no data
211	* (because it wouldn't fit). The next page contains
212	* the data.
213	*
214	* Page format it:
215	* KEY_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
216	*
217	* KEY_OFF -- offset of the beginning of the key
218	* FULL_KEY -- 2
219	* OVFL_PAGENO - page number of the next overflow page
220	* OVFLPAGE -- 0
221	*
222	* Case 2:
223	* This page contains no key, but part of a large
224	* data field, which is continued on the next page.
225	*
226	* Page format it:
227	* DATA_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
228	*
229	* KEY_OFF -- offset of the beginning of the data on
230	* this page
231	* FULL_KEY -- 2
232	* OVFL_PAGENO - page number of the next overflow page
233	* OVFLPAGE -- 0
234	*
235	* FULL_KEY_DATA
236	* This must be the first key/data pair on the page.
237	* There are two cases:
238	*
239	* Case 1:
240	* This page contains a key and the beginning of the
241	* data field, but the data field is continued on the
242	* next page.
243	*
244	* Page format is:
245	* KEY_OFF FULL_KEY_DATA OVFL_PAGENO DATA_OFF
246	*
247	* KEY_OFF -- offset of the beginning of the key
248	* FULL_KEY_DATA -- 3
249	* OVFL_PAGENO - page number of the next overflow page
250	* DATA_OFF -- offset of the beginning of the data
251	*
252	* Case 2:
253	* This page contains the last page of a big data pair.
254	* There is no key, only the tail end of the data
255	* on this page.
256	*
257	* Page format is:
258	* DATA_OFF FULL_KEY_DATA <OVFL_PAGENO> <OVFLPAGE>
259	*
260	* DATA_OFF -- offset of the beginning of the data on
261	* this page
262	* FULL_KEY_DATA -- 3
263	* OVFL_PAGENO - page number of the next overflow page
264	* OVFLPAGE -- 0
265	*
266	* OVFL_PAGENO and OVFLPAGE are optional (they are
267	* not present if there is no next page).
268	*/
269
270	#define OVFLPAGE 0
271	#define PARTIAL_KEY 1
272	#define FULL_KEY 2
273	#define FULL_KEY_DATA 3
274	#define REAL_KEY 4
275
276	/* Short hands for accessing structure */
277	#define BSIZE hdr.bsize
278	#define BSHIFT hdr.bshift
279	#define DSIZE hdr.dsize
280	#define SGSIZE hdr.ssize
281	#define SSHIFT hdr.sshift
282	#define LORDER hdr.lorder
283	#define OVFL_POINT hdr.ovfl_point
284	#define LAST_FREED hdr.last_freed
285	#define MAX_BUCKET hdr.max_bucket
286	#define FFACTOR hdr.ffactor
287	#define HIGH_MASK hdr.high_mask
288	#define LOW_MASK hdr.low_mask
289	#define NKEYS hdr.nkeys
290	#define HDRPAGES hdr.hdrpages
291	#define SPARES hdr.spares
292	#define BITMAPS hdr.bitmaps
293	#define VERSION hdr.version
294	#define MAGIC hdr.magic
295	#define NEXT_FREE hdr.next_free
296	#define H_CHARKEY hdr.h_charkey