lib/libc/DB/btree/bt_search.c

   1 /*-
   2  * Copyright (c) 1990 The Regents of the University of California.
   3  * 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 5.9 (Berkeley) 2/14/93";
  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 }