db.1.85/btree/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
  41 #include <sys/types.h>
  42
  43 #include <stdio.h>
  44
  45 #include <db.h>
  46 #include "btree.h"
  47
  48 static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *));
  49 static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *));
  50
  51 /*
  52  * __bt_search --
  53  *      Search a btree for a key.
  54  *
  55  * Parameters:
  56  *      t:      tree to search
  57  *      key:    key to find
  58  *      exactp: pointer to exact match flag
  59  *
  60  * Returns:
  61  *      The EPG for matching record, if any, or the EPG for the location
  62  *      of the key, if it were inserted into the tree, is entered into
  63  *      the bt_cur field of the tree.  A pointer to the field is returned.
  64  */
  65 EPG *
  66 __bt_search(t, key, exactp)
  67         BTREE *t;
  68         const DBT *key;
  69         int *exactp;
  70 {
  71         PAGE *h;
  72         indx_t base, index, lim;
  73         pgno_t pg;
  74         int cmp;
  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                 t->bt_cur.page = h;
  83                 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
  84                         t->bt_cur.index = index = base + (lim >> 1);
  85                         if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) {
  86                                 if (h->flags & P_BLEAF) {
  87                                         *exactp = 1;
  88                                         return (&t->bt_cur);
  89                                 }
  90                                 goto next;
  91                         }
  92                         if (cmp > 0) {
  93                                 base = index + 1;
  94                                 --lim;
  95                         }
  96                 }
  97
  98                 /*
  99                  * If it's a leaf page, we're almost done.  If no duplicates
 100                  * are allowed, or we have an exact match, we're done.  Else,
 101                  * it's possible that there were matching keys on this page,
 102                  * which later deleted, and we're on a page with no matches
 103                  * while there are matches on other pages.  If at the start or
 104                  * end of a page, check the adjacent page.
 105                  */
 106                 if (h->flags & P_BLEAF) {
 107                         if (!F_ISSET(t, B_NODUPS)) {
 108                                 if (base == 0 &&
 109                                     h->prevpg != P_INVALID &&
 110                                     __bt_sprev(t, h, key, exactp))
 111                                         return (&t->bt_cur);
 112                                 if (base == NEXTINDEX(h) &&
 113                                     h->nextpg != P_INVALID &&
 114                                     __bt_snext(t, h, key, exactp))
 115                                         return (&t->bt_cur);
 116                         }
 117                         *exactp = 0;
 118                         t->bt_cur.index = base;
 119                         return (&t->bt_cur);
 120                 }
 121
 122                 /*
 123                  * No match found.  Base is the smallest index greater than
 124                  * key and may be zero or a last + 1 index.  If it's non-zero,
 125                  * decrement by one, and record the internal page which should
 126                  * be a parent page for the key.  If a split later occurs, the
 127                  * inserted page will be to the right of the saved page.
 128                  */
 129                 index = base ? base - 1 : base;
 130
 131 next:           BT_PUSH(t, h->pgno, index);
 132                 pg = GETBINTERNAL(h, index)->pgno;
 133                 mpool_put(t->bt_mp, h, 0);
 134         }
 135 }
 136
 137 /*
 138  * __bt_snext --
 139  *      Check for an exact match after the key.
 140  *
 141  * Parameters:
 142  *      t:      tree
 143  *      h:      current page
 144  *      key:    key
 145  *      exactp: pointer to exact match flag
 146  *
 147  * Returns:
 148  *      If an exact match found.
 149  */
 150 static int
 151 __bt_snext(t, h, key, exactp)
 152         BTREE *t;
 153         PAGE *h;
 154         const DBT *key;
 155         int *exactp;
 156 {
 157         EPG e;
 158
 159         /*
 160          * Get the next page.  The key is either an exact
 161          * match, or not as good as the one we already have.
 162          */
 163         if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
 164                 return (0);
 165         e.index = 0;
 166         if (__bt_cmp(t, key, &e) == 0) {
 167                 mpool_put(t->bt_mp, h, 0);
 168                 t->bt_cur = e;
 169                 *exactp = 1;
 170                 return (1);
 171         }
 172         mpool_put(t->bt_mp, e.page, 0);
 173         return (0);
 174 }
 175
 176 /*
 177  * __bt_sprev --
 178  *      Check for an exact match before the key.
 179  *
 180  * Parameters:
 181  *      t:      tree
 182  *      h:      current page
 183  *      key:    key
 184  *      exactp: pointer to exact match flag
 185  *
 186  * Returns:
 187  *      If an exact match found.
 188  */
 189 static int
 190 __bt_sprev(t, h, key, exactp)
 191         BTREE *t;
 192         PAGE *h;
 193         const DBT *key;
 194         int *exactp;
 195 {
 196         EPG e;
 197
 198         /*
 199          * Get the previous page.  The key is either an exact
 200          * match, or not as good as the one we already have.
 201          */
 202         if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
 203                 return (0);
 204         e.index = NEXTINDEX(e.page) - 1;
 205         if (__bt_cmp(t, key, &e) == 0) {
 206                 mpool_put(t->bt_mp, h, 0);
 207                 t->bt_cur = e;
 208                 *exactp = 1;
 209                 return (1);
 210         }
 211         mpool_put(t->bt_mp, e.page, 0);
 212         return (0);
 213 }