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  * 4. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #if defined(LIBC_SCCS) && !defined(lint)
  34 static char sccsid[] = "@(#)bt_search.c 8.8 (Berkeley) 7/31/94";
  35 #endif /* LIBC_SCCS and not lint */
  36 #include <sys/cdefs.h>
  37 __FBSDID("$FreeBSD: src/lib/libc/db/btree/bt_search.c,v 1.5 2009/03/03 02:16:12 delphij Exp $");
  38
  39 #include <sys/types.h>
  40
  41 #include <stdio.h>
  42
  43 #include <db.h>
  44 #include "btree.h"
  45
  46 static int __bt_snext(BTREE *, PAGE *, const DBT *, int *);
  47 static int __bt_sprev(BTREE *, PAGE *, const DBT *, int *);
  48
  49 /*
  50  * __bt_search --
  51  *      Search a btree for a key.
  52  *
  53  * Parameters:
  54  *      t:      tree to search
  55  *      key:    key to find
  56  *      exactp: pointer to exact match flag
  57  *
  58  * Returns:
  59  *      The EPG for matching record, if any, or the EPG for the location
  60  *      of the key, if it were inserted into the tree, is entered into
  61  *      the bt_cur field of the tree.  A pointer to the field is returned.
  62  */
  63 EPG *
  64 __bt_search(BTREE *t, const DBT *key, int *exactp)
  65 {
  66         PAGE *h;
  67         indx_t base, idx, lim;
  68         pgno_t pg;
  69         int cmp;
  70
  71         BT_CLR(t);
  72         for (pg = P_ROOT;;) {
  73                 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
  74                         return (NULL);
  75
  76                 /* Do a binary search on the current page. */
  77                 t->bt_cur.page = h;
  78                 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
  79                         t->bt_cur.index = idx = base + (lim >> 1);
  80                         if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) {
  81                                 if (h->flags & P_BLEAF) {
  82                                         *exactp = 1;
  83                                         return (&t->bt_cur);
  84                                 }
  85                                 goto next;
  86                         }
  87                         if (cmp > 0) {
  88                                 base = idx + 1;
  89                                 --lim;
  90                         }
  91                 }
  92
  93                 /*
  94                  * If it's a leaf page, we're almost done.  If no duplicates
  95                  * are allowed, or we have an exact match, we're done.  Else,
  96                  * it's possible that there were matching keys on this page,
  97                  * which later deleted, and we're on a page with no matches
  98                  * while there are matches on other pages.  If at the start or
  99                  * end of a page, check the adjacent page.
 100                  */
 101                 if (h->flags & P_BLEAF) {
 102                         if (!F_ISSET(t, B_NODUPS)) {
 103                                 if (base == 0 &&
 104                                     h->prevpg != P_INVALID &&
 105                                     __bt_sprev(t, h, key, exactp))
 106                                         return (&t->bt_cur);
 107                                 if (base == NEXTINDEX(h) &&
 108                                     h->nextpg != P_INVALID &&
 109                                     __bt_snext(t, h, key, exactp))
 110                                         return (&t->bt_cur);
 111                         }
 112                         *exactp = 0;
 113                         t->bt_cur.index = base;
 114                         return (&t->bt_cur);
 115                 }
 116
 117                 /*
 118                  * No match found.  Base is the smallest index greater than
 119                  * key and may be zero or a last + 1 index.  If it's non-zero,
 120                  * decrement by one, and record the internal page which should
 121                  * be a parent page for the key.  If a split later occurs, the
 122                  * inserted page will be to the right of the saved page.
 123                  */
 124                 idx = base ? base - 1 : base;
 125
 126 next:           BT_PUSH(t, h->pgno, idx);
 127                 pg = GETBINTERNAL(h, idx)->pgno;
 128                 mpool_put(t->bt_mp, h, 0);
 129         }
 130 }
 131
 132 /*
 133  * __bt_snext --
 134  *      Check for an exact match after the key.
 135  *
 136  * Parameters:
 137  *      t:      tree
 138  *      h:      current page
 139  *      key:    key
 140  *      exactp: pointer to exact match flag
 141  *
 142  * Returns:
 143  *      If an exact match found.
 144  */
 145 static int
 146 __bt_snext(BTREE *t, PAGE *h, const DBT *key, int *exactp)
 147 {
 148         EPG e;
 149
 150         /*
 151          * Get the next page.  The key is either an exact
 152          * match, or not as good as the one we already have.
 153          */
 154         if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
 155                 return (0);
 156         e.index = 0;
 157         if (__bt_cmp(t, key, &e) == 0) {
 158                 mpool_put(t->bt_mp, h, 0);
 159                 t->bt_cur = e;
 160                 *exactp = 1;
 161                 return (1);
 162         }
 163         mpool_put(t->bt_mp, e.page, 0);
 164         return (0);
 165 }
 166
 167 /*
 168  * __bt_sprev --
 169  *      Check for an exact match before the key.
 170  *
 171  * Parameters:
 172  *      t:      tree
 173  *      h:      current page
 174  *      key:    key
 175  *      exactp: pointer to exact match flag
 176  *
 177  * Returns:
 178  *      If an exact match found.
 179  */
 180 static int
 181 __bt_sprev(BTREE *t, PAGE *h, const DBT *key, int *exactp)
 182 {
 183         EPG e;
 184
 185         /*
 186          * Get the previous page.  The key is either an exact
 187          * match, or not as good as the one we already have.
 188          */
 189         if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
 190                 return (0);
 191         e.index = NEXTINDEX(e.page) - 1;
 192         if (__bt_cmp(t, key, &e) == 0) {
 193                 mpool_put(t->bt_mp, h, 0);
 194                 t->bt_cur = e;
 195                 *exactp = 1;
 196                 return (1);
 197         }
 198         mpool_put(t->bt_mp, e.page, 0);
 199         return (0);
 200 }