db/btree/FreeBSD/bt_search.c

   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  * 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 8.8 (Berkeley) 7/31/94";
  39 #endif /* LIBC_SCCS and not lint */
  40 #include <sys/cdefs.h>
  41 __FBSDID("$FreeBSD: src/lib/libc/db/btree/bt_search.c,v 1.2 2002/03/21 22:46:25 obrien Exp $");
  42
  43 #include <sys/types.h>
  44
  45 #include <stdio.h>
  46
  47 #include <db.h>
  48 #include "btree.h"
  49
  50 static int __bt_snext(BTREE *, PAGE *, const DBT *, int *);
  51 static int __bt_sprev(BTREE *, PAGE *, const DBT *, int *);
  52
  53 /*
  54  * __bt_search --
  55  *      Search a btree for a key.
  56  *
  57  * Parameters:
  58  *      t:      tree to search
  59  *      key:    key to find
  60  *      exactp: pointer to exact match flag
  61  *
  62  * Returns:
  63  *      The EPG for matching record, if any, or the EPG for the location
  64  *      of the key, if it were inserted into the tree, is entered into
  65  *      the bt_cur field of the tree.  A pointer to the field is returned.
  66  */
  67 EPG *
  68 __bt_search(t, key, exactp)
  69         BTREE *t;
  70         const DBT *key;
  71         int *exactp;
  72 {
  73         PAGE *h;
  74         indx_t base, index, lim;
  75         pgno_t pg;
  76         int cmp;
  77
  78         BT_CLR(t);
  79         for (pg = P_ROOT;;) {
  80                 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
  81                         return (NULL);
  82
  83                 /* Do a binary search on the current page. */
  84                 t->bt_cur.page = h;
  85                 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
  86                         t->bt_cur.index = index = base + (lim >> 1);
  87                         if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) {
  88                                 if (h->flags & P_BLEAF) {
  89                                         *exactp = 1;
  90                                         return (&t->bt_cur);
  91                                 }
  92                                 goto next;
  93                         }
  94                         if (cmp > 0) {
  95                                 base = index + 1;
  96                                 --lim;
  97                         }
  98                 }
  99
 100                 /*
 101                  * If it's a leaf page, we're almost done.  If no duplicates
 102                  * are allowed, or we have an exact match, we're done.  Else,
 103                  * it's possible that there were matching keys on this page,
 104                  * which later deleted, and we're on a page with no matches
 105                  * while there are matches on other pages.  If at the start or
 106                  * end of a page, check the adjacent page.
 107                  */
 108                 if (h->flags & P_BLEAF) {
 109                         if (!F_ISSET(t, B_NODUPS)) {
 110                                 if (base == 0 &&
 111                                     h->prevpg != P_INVALID &&
 112                                     __bt_sprev(t, h, key, exactp))
 113                                         return (&t->bt_cur);
 114                                 if (base == NEXTINDEX(h) &&
 115                                     h->nextpg != P_INVALID &&
 116                                     __bt_snext(t, h, key, exactp))
 117                                         return (&t->bt_cur);
 118                         }
 119                         *exactp = 0;
 120                         t->bt_cur.index = base;
 121                         return (&t->bt_cur);
 122                 }
 123
 124                 /*
 125                  * No match found.  Base is the smallest index greater than
 126                  * key and may be zero or a last + 1 index.  If it's non-zero,
 127                  * decrement by one, and record the internal page which should
 128                  * be a parent page for the key.  If a split later occurs, the
 129                  * inserted page will be to the right of the saved page.
 130                  */
 131                 index = base ? base - 1 : base;
 132
 133 next:           BT_PUSH(t, h->pgno, index);
 134                 pg = GETBINTERNAL(h, index)->pgno;
 135                 mpool_put(t->bt_mp, h, 0);
 136         }
 137 }
 138
 139 /*
 140  * __bt_snext --
 141  *      Check for an exact match after the key.
 142  *
 143  * Parameters:
 144  *      t:      tree
 145  *      h:      current page
 146  *      key:    key
 147  *      exactp: pointer to exact match flag
 148  *
 149  * Returns:
 150  *      If an exact match found.
 151  */
 152 static int
 153 __bt_snext(t, h, key, exactp)
 154         BTREE *t;
 155         PAGE *h;
 156         const DBT *key;
 157         int *exactp;
 158 {
 159         EPG e;
 160
 161         /*
 162          * Get the next page.  The key is either an exact
 163          * match, or not as good as the one we already have.
 164          */
 165         if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
 166                 return (0);
 167         e.index = 0;
 168         if (__bt_cmp(t, key, &e) == 0) {
 169                 mpool_put(t->bt_mp, h, 0);
 170                 t->bt_cur = e;
 171                 *exactp = 1;
 172                 return (1);
 173         }
 174         mpool_put(t->bt_mp, e.page, 0);
 175         return (0);
 176 }
 177
 178 /*
 179  * __bt_sprev --
 180  *      Check for an exact match before the key.
 181  *
 182  * Parameters:
 183  *      t:      tree
 184  *      h:      current page
 185  *      key:    key
 186  *      exactp: pointer to exact match flag
 187  *
 188  * Returns:
 189  *      If an exact match found.
 190  */
 191 static int
 192 __bt_sprev(t, h, key, exactp)
 193         BTREE *t;
 194         PAGE *h;
 195         const DBT *key;
 196         int *exactp;
 197 {
 198         EPG e;
 199
 200         /*
 201          * Get the previous page.  The key is either an exact
 202          * match, or not as good as the one we already have.
 203          */
 204         if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
 205                 return (0);
 206         e.index = NEXTINDEX(e.page) - 1;
 207         if (__bt_cmp(t, key, &e) == 0) {
 208                 mpool_put(t->bt_mp, h, 0);
 209                 t->bt_cur = e;
 210                 *exactp = 1;
 211                 return (1);
 212         }
 213         mpool_put(t->bt_mp, e.page, 0);
 214         return (0);
 215 }