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bt_search.c revision 1.1 
      1 /*-
      2  * Copyright (c) 1990, 1993
      3  *	The Regents of the University of California.  All rights reserved.
      4  *
      5  * This code is derived from software contributed to Berkeley by
      6  * Mike Olson.
      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 
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 static char sccsid[] = "@(#)bt_search.c	8.1 (Berkeley) 6/4/93";
     39 #endif /* LIBC_SCCS and not lint */
     40 
     41 #include <sys/types.h>
     42 
     43 #include <stdio.h>
     44 
     45 #include <db.h>
     46 #include "btree.h"
     47 
     48 /*
     49  * __BT_SEARCH -- Search a btree for a key.
     50  *
     51  * Parameters:
     52  *	t:	tree to search
     53  *	key:	key to find
     54  *	exactp:	pointer to exact match flag
     55  *
     56  * Returns:
     57  *	EPG for matching record, if any, or the EPG for the location of the
     58  *	key, if it were inserted into the tree.
     59  *
     60  * Warnings:
     61  *	The EPG returned is in static memory, and will be overwritten by the
     62  *	next search of any kind in any tree.
     63  */
     64 EPG *
     65 __bt_search(t, key, exactp)
     66 	BTREE *t;
     67 	const DBT *key;
     68 	int *exactp;
     69 {
     70 	register indx_t index;
     71 	register int base, cmp, lim;
     72 	register PAGE *h;
     73 	pgno_t pg;
     74 	static EPG e;
     75 
     76 	BT_CLR(t);
     77 	for (pg = P_ROOT;;) {
     78 		if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
     79 			return (NULL);
     80 
     81 		/* Do a binary search on the current page. */
     82 		e.page = h;
     83 		for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
     84 			e.index = index = base + (lim >> 1);
     85 			if ((cmp = __bt_cmp(t, key, &e)) == 0) {
     86 				if (h->flags & P_BLEAF) {
     87 					*exactp = 1;
     88 					return (&e);
     89 				}
     90 				goto next;
     91 			}
     92 			if (cmp > 0) {
     93 				base = index + 1;
     94 				--lim;
     95 			}
     96 		}
     97 
     98 		/* If it's a leaf page, we're done. */
     99 		if (h->flags & P_BLEAF) {
    100 			e.index = base;
    101 			*exactp = 0;
    102 			return (&e);
    103 		}
    104 
    105 		/*
    106 		 * No match found.  Base is the smallest index greater than
    107 		 * key and may be zero or a last + 1 index.  If it's non-zero,
    108 		 * decrement by one, and record the internal page which should
    109 		 * be a parent page for the key.  If a split later occurs, the
    110 		 * inserted page will be to the right of the saved page.
    111 		 */
    112 		index = base ? base - 1 : base;
    113 
    114 next:		if (__bt_push(t, h->pgno, index) == RET_ERROR)
    115 			return (NULL);
    116 		pg = GETBINTERNAL(h, index)->pgno;
    117 		mpool_put(t->bt_mp, h, 0);
    118 	}
    119 }
    120