[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.
 * 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 1.9 2009/03/28 05:45:29 delphij 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 */
	int32_t		magic;		/* Magic NO for hash tables */
	int32_t		version;	/* Version ID */
	u_int32_t	lorder;		/* Byte Order */
	int32_t		bsize;		/* Bucket/Page Size */
	int32_t		bshift;		/* Bucket shift */
	int32_t		dsize;		/* Directory Size */
	int32_t		ssize;		/* Segment Size */
	int32_t		sshift;		/* Segment shift */
	int32_t		ovfl_point;	/* Where overflow pages are being 
					 * allocated */
	int32_t		last_freed;	/* Last overflow page freed */
	u_int32_t	max_bucket;	/* ID of Maximum bucket in use */
	u_int32_t	high_mask;	/* Mask to modulo into entire table */
	u_int32_t	low_mask;	/* Mask to modulo into lower half of 
					 * table */
	u_int32_t	ffactor;	/* Fill factor */
	int32_t		nkeys;		/* Number of keys in hash table */
	int32_t		hdrpages;	/* Size of table header */
	int32_t		h_charkey;	/* value of hash(CHARKEY) */
#define NCACHED	32			/* number of bit maps and spare 
					 * points */
	int32_t		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.
224c7076 A	16	* 4. Neither the name of the University nor the names of its contributors
	17	* may be used to endorse or promote products derived from this software
	18	* without specific prior written permission.
	19	*
	20	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	21	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	22	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	23	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	24	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	25	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	26	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	27	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	28	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	29	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	30	* SUCH DAMAGE.
	31	*
	32	* @(#)hash.h 8.3 (Berkeley) 5/31/94
1f2f436a	33	* $FreeBSD: src/lib/libc/db/hash/hash.h,v 1.9 2009/03/28 05:45:29 delphij Exp $
224c7076 A	34	*/
	35
	36	/* Operations */
	37	typedef enum {
	38	HASH_GET, HASH_PUT, HASH_PUTNEW, HASH_DELETE, HASH_FIRST, HASH_NEXT
	39	} ACTION;
	40
	41	/* Buffer Management structures */
	42	typedef struct _bufhead BUFHEAD;
	43
	44	struct _bufhead {
	45	BUFHEAD prev; / LRU links */
	46	BUFHEAD next; / LRU links */
	47	BUFHEAD ovfl; / Overflow page buffer header */
	48	u_int32_t addr; /* Address of this page */
	49	char page; / Actual page data */
	50	char flags;
	51	#define BUF_MOD 0x0001
	52	#define BUF_DISK 0x0002
	53	#define BUF_BUCKET 0x0004
	54	#define BUF_PIN 0x0008
	55	};
	56
	57	#define IS_BUCKET(X) ((X) & BUF_BUCKET)
	58
	59	typedef BUFHEAD **SEGMENT;
	60
	61	/* Hash Table Information */
	62	typedef struct hashhdr { /* Disk resident portion */
1f2f436a A	63	int32_t magic; /* Magic NO for hash tables */
1f2f436a A	64	int32_t version; /* Version ID */
224c7076	65	u_int32_t lorder; /* Byte Order */
1f2f436a A	66	int32_t bsize; /* Bucket/Page Size */
	67	int32_t bshift; /* Bucket shift */
	68	int32_t dsize; /* Directory Size */
	69	int32_t ssize; /* Segment Size */
	70	int32_t sshift; /* Segment shift */
	71	int32_t ovfl_point; /* Where overflow pages are being
224c7076	72	* allocated */
1f2f436a A	73	int32_t last_freed; /* Last overflow page freed */
	74	u_int32_t max_bucket; /* ID of Maximum bucket in use */
	75	u_int32_t high_mask; /* Mask to modulo into entire table */
	76	u_int32_t low_mask; /* Mask to modulo into lower half of
224c7076	77	* table */
1f2f436a A	78	u_int32_t ffactor; /* Fill factor */
	79	int32_t nkeys; /* Number of keys in hash table */
	80	int32_t hdrpages; /* Size of table header */
	81	int32_t h_charkey; /* value of hash(CHARKEY) */
224c7076 A	82	#define NCACHED 32 /* number of bit maps and spare
224c7076 A	83	* points */
1f2f436a	84	int32_t spares[NCACHED];/* spare pages for overflow */
224c7076 A	85	u_int16_t bitmaps[NCACHED]; /* address of overflow page
	86	* bitmaps */
	87	} HASHHDR;
	88
	89	typedef struct htab { /* Memory resident data structure */
	90	HASHHDR hdr; /* Header */
	91	int nsegs; /* Number of allocated segments */
	92	int exsegs; /* Number of extra allocated
	93	* segments */
	94	u_int32_t /* Hash function */
	95	(hash)(const void , size_t);
	96	int flags; /* Flag values */
	97	int fp; /* File pointer */
	98	char tmp_buf; / Temporary Buffer for BIG data */
	99	char tmp_key; / Temporary Buffer for BIG keys */
	100	BUFHEAD cpage; / Current page */
	101	int cbucket; /* Current bucket */
	102	int cndx; /* Index of next item on cpage */
	103	int error; /* Error Number -- for DBM
	104	* compatibility */
	105	int new_file; /* Indicates if fd is backing store
	106	* or no */
	107	int save_file; /* Indicates whether we need to flush
	108	* file at
	109	* exit */
	110	u_int32_t mapp[NCACHED]; / Pointers to page maps */
	111	int nmaps; /* Initial number of bitmaps */
	112	int nbufs; /* Number of buffers left to
	113	* allocate */
	114	BUFHEAD bufhead; /* Header of buffer lru list */
	115	SEGMENT dir; / Hash Bucket directory */
	116	/* other flags */
	117	int nextkey_eof :1; /* dbm_nextkey() reached EOF */
	118	} HTAB;
	119
	120	/*
	121	* Constants
	122	*/
	123	#define MAX_BSIZE 65536 /* 2^16 */
	124	#define MIN_BUFFERS 6
	125	#define MINHDRSIZE 512
	126	#define DEF_BUFSIZE 65536 /* 64 K */
	127	#define DEF_BUCKET_SIZE 4096
	128	#define DEF_BUCKET_SHIFT 12 /* log2(BUCKET) */
	129	#define DEF_SEGSIZE 256
	130	#define DEF_SEGSIZE_SHIFT 8 /* log2(SEGSIZE) */
	131	#define DEF_DIRSIZE 256
	132	#define DEF_FFACTOR 65536
	133	#define MIN_FFACTOR 4
	134	#define SPLTMAX 8
	135	#define CHARKEY "%$sniglet^&"
	136	#define NUMKEY 1038583
	137	#define BYTE_SHIFT 3
	138	#define INT_TO_BYTE 2
	139	#define INT_BYTE_SHIFT 5
	140	#define ALL_SET ((u_int32_t)0xFFFFFFFF)
	141	#define ALL_CLEAR 0
	142
	143	#define PTROF(X) ((BUFHEAD *)((ptrdiff_t)(X)&~0x3))
	144	#define ISMOD(X) ((u_int32_t)(ptrdiff_t)(X)&0x1)
	145	#define DOMOD(X) ((X) = (char *)((ptrdiff_t)(X)\|0x1))
	146	#define ISDISK(X) ((u_int32_t)(ptrdiff_t)(X)&0x2)
	147	#define DODISK(X) ((X) = (char *)((ptrdiff_t)(X)\|0x2))
	148
149	#define BITS_PER_MAP 32
150
151	/* Given the address of the beginning of a big map, clear/set the nth bit */
152	#define CLRBIT(A, N) ((A)[(N)/BITS_PER_MAP] &= ~(1<<((N)%BITS_PER_MAP)))
153	#define SETBIT(A, N) ((A)[(N)/BITS_PER_MAP] \|= (1<<((N)%BITS_PER_MAP)))
154	#define ISSET(A, N) ((A)[(N)/BITS_PER_MAP] & (1<<((N)%BITS_PER_MAP)))
155
156	/* Overflow management */
157	/*
158	* Overflow page numbers are allocated per split point. At each doubling of
159	* the table, we can allocate extra pages. So, an overflow page number has
160	* the top 5 bits indicate which split point and the lower 11 bits indicate
161	* which page at that split point is indicated (pages within split points are
162	* numberered starting with 1).
163	*/
164
165	#define SPLITSHIFT 11
166	#define SPLITMASK 0x7FF
167	#define SPLITNUM(N) (((u_int32_t)(N)) >> SPLITSHIFT)
168	#define OPAGENUM(N) ((N) & SPLITMASK)
169	#define OADDR_OF(S,O) ((u_int32_t)((u_int32_t)(S) << SPLITSHIFT) + (O))
170
171	#define BUCKET_TO_PAGE(B) \
172	(B) + hashp->HDRPAGES + ((B) ? hashp->SPARES[__log2((B)+1)-1] : 0)
173	#define OADDR_TO_PAGE(B) \
174	BUCKET_TO_PAGE ( (1 << SPLITNUM((B))) -1 ) + OPAGENUM((B));
175
176	/*
177	* page.h contains a detailed description of the page format.
178	*
179	* Normally, keys and data are accessed from offset tables in the top of
180	* each page which point to the beginning of the key and data. There are
181	* four flag values which may be stored in these offset tables which indicate
182	* the following:
183	*
184	*
185	* OVFLPAGE Rather than a key data pair, this pair contains
186	* the address of an overflow page. The format of
187	* the pair is:
188	* OVERFLOW_PAGE_NUMBER OVFLPAGE
189	*
190	* PARTIAL_KEY This must be the first key/data pair on a page
191	* and implies that page contains only a partial key.
192	* That is, the key is too big to fit on a single page
193	* so it starts on this page and continues on the next.
194	* The format of the page is:
195	* KEY_OFF PARTIAL_KEY OVFL_PAGENO OVFLPAGE
196	*
197	* KEY_OFF -- offset of the beginning of the key
198	* PARTIAL_KEY -- 1
199	* OVFL_PAGENO - page number of the next overflow page
200	* OVFLPAGE -- 0
201	*
202	* FULL_KEY This must be the first key/data pair on the page. It
203	* is used in two cases.
204	*
205	* Case 1:
206	* There is a complete key on the page but no data
207	* (because it wouldn't fit). The next page contains
208	* the data.
209	*
210	* Page format it:
211	* KEY_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
212	*
213	* KEY_OFF -- offset of the beginning of the key
214	* FULL_KEY -- 2
215	* OVFL_PAGENO - page number of the next overflow page
216	* OVFLPAGE -- 0
217	*
218	* Case 2:
219	* This page contains no key, but part of a large
220	* data field, which is continued on the next page.
221	*
222	* Page format it:
223	* DATA_OFF FULL_KEY OVFL_PAGENO OVFL_PAGE
224	*
225	* KEY_OFF -- offset of the beginning of the data on
226	* this page
227	* FULL_KEY -- 2
228	* OVFL_PAGENO - page number of the next overflow page
229	* OVFLPAGE -- 0
230	*
231	* FULL_KEY_DATA
232	* This must be the first key/data pair on the page.
233	* There are two cases:
234	*
235	* Case 1:
236	* This page contains a key and the beginning of the
237	* data field, but the data field is continued on the
238	* next page.
239	*
240	* Page format is:
241	* KEY_OFF FULL_KEY_DATA OVFL_PAGENO DATA_OFF
242	*
243	* KEY_OFF -- offset of the beginning of the key
244	* FULL_KEY_DATA -- 3
245	* OVFL_PAGENO - page number of the next overflow page
246	* DATA_OFF -- offset of the beginning of the data
247	*
248	* Case 2:
249	* This page contains the last page of a big data pair.
250	* There is no key, only the tail end of the data
251	* on this page.
252	*
253	* Page format is:
254	* DATA_OFF FULL_KEY_DATA <OVFL_PAGENO> <OVFLPAGE>
255	*
256	* DATA_OFF -- offset of the beginning of the data on
257	* this page
258	* FULL_KEY_DATA -- 3
259	* OVFL_PAGENO - page number of the next overflow page
260	* OVFLPAGE -- 0
261	*
262	* OVFL_PAGENO and OVFLPAGE are optional (they are
263	* not present if there is no next page).
264	*/
265
266	#define OVFLPAGE 0
267	#define PARTIAL_KEY 1
268	#define FULL_KEY 2
269	#define FULL_KEY_DATA 3
270	#define REAL_KEY 4
271
272	/* Short hands for accessing structure */
273	#define BSIZE hdr.bsize
274	#define BSHIFT hdr.bshift
275	#define DSIZE hdr.dsize
276	#define SGSIZE hdr.ssize
277	#define SSHIFT hdr.sshift
278	#define LORDER hdr.lorder
279	#define OVFL_POINT hdr.ovfl_point
280	#define LAST_FREED hdr.last_freed
281	#define MAX_BUCKET hdr.max_bucket
282	#define FFACTOR hdr.ffactor
283	#define HIGH_MASK hdr.high_mask
284	#define LOW_MASK hdr.low_mask
285	#define NKEYS hdr.nkeys
286	#define HDRPAGES hdr.hdrpages
287	#define SPARES hdr.spares
288	#define BITMAPS hdr.bitmaps
289	#define VERSION hdr.version
290	#define MAGIC hdr.magic
291	#define NEXT_FREE hdr.next_free
292	#define H_CHARKEY hdr.h_charkey