lib/libc/db/btree/bt_search.c

   1 /*      $NetBSD: bt_search.c,v 1.16 2008/09/10 17:52:35 joerg Exp $     */
   2
   3 /*-
   4  * Copyright (c) 1990, 1993, 1994
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * Mike Olson.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #if HAVE_NBTOOL_CONFIG_H
  36 #include "nbtool_config.h"
  37 #endif
  38
  39 #include <sys/cdefs.h>
  40 __RCSID("$NetBSD: bt_search.c,v 1.16 2008/09/10 17:52:35 joerg Exp $");
  41
  42 #include "namespace.h"
  43 #include <sys/types.h>
  44
  45 #include <assert.h>
  46 #include <stdio.h>
  47
  48 #include <db.h>
  49 #include "btree.h"
  50
  51 static int __bt_snext(BTREE *, PAGE *, const DBT *, int *);
  52 static int __bt_sprev(BTREE *, PAGE *, const DBT *, int *);
  53
  54 /*
  55  * __bt_search --
  56  *      Search a btree for a key.
  57  *
  58  * Parameters:
  59  *      t:      tree to search
  60  *      key:    key to find
  61  *      exactp: pointer to exact match flag
  62  *
  63  * Returns:
  64  *      The EPG for matching record, if any, or the EPG for the location
  65  *      of the key, if it were inserted into the tree, is entered into
  66  *      the bt_cur field of the tree.  A pointer to the field is returned.
  67  */
  68 EPG *
  69 __bt_search(BTREE *t, const DBT *key, int *exactp)
  70 {
  71         PAGE *h;
  72         indx_t base, idx, 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 = idx = base + ((uint32_t)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 = idx + 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                 idx = base ? base - 1 : base;
 130
 131 next:           BT_PUSH(t, h->pgno, idx);
 132                 pg = GETBINTERNAL(h, idx)->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(BTREE *t, PAGE *h, const DBT *key, int *exactp)
 152 {
 153         EPG e;
 154
 155         /*
 156          * Get the next page.  The key is either an exact
 157          * match, or not as good as the one we already have.
 158          */
 159         if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
 160                 return (0);
 161         e.index = 0;
 162         if (__bt_cmp(t, key, &e) == 0) {
 163                 mpool_put(t->bt_mp, h, 0);
 164                 t->bt_cur = e;
 165                 *exactp = 1;
 166                 return (1);
 167         }
 168         mpool_put(t->bt_mp, e.page, 0);
 169         return (0);
 170 }
 171
 172 /*
 173  * __bt_sprev --
 174  *      Check for an exact match before the key.
 175  *
 176  * Parameters:
 177  *      t:      tree
 178  *      h:      current page
 179  *      key:    key
 180  *      exactp: pointer to exact match flag
 181  *
 182  * Returns:
 183  *      If an exact match found.
 184  */
 185 static int
 186 __bt_sprev(BTREE *t, PAGE *h, const DBT *key, int *exactp)
 187 {
 188         EPG e;
 189
 190         /*
 191          * Get the previous page.  The key is either an exact
 192          * match, or not as good as the one we already have.
 193          */
 194         if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
 195                 return (0);
 196         e.index = NEXTINDEX(e.page) - 1;
 197         if (__bt_cmp(t, key, &e) == 0) {
 198                 mpool_put(t->bt_mp, h, 0);
 199                 t->bt_cur = e;
 200                 *exactp = 1;
 201                 return (1);
 202         }
 203         mpool_put(t->bt_mp, e.page, 0);
 204         return (0);
 205 }