db.subproj/btree.subproj/bt_search.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23  * Copyright (c) 1990, 1993
  24  *      The Regents of the University of California.  All rights reserved.
  25  *
  26  * This code is derived from software contributed to Berkeley by
  27  * Mike Olson.
  28  *
  29  * Redistribution and use in source and binary forms, with or without
  30  * modification, are permitted provided that the following conditions
  31  * are met:
  32  * 1. Redistributions of source code must retain the above copyright
  33  *    notice, this list of conditions and the following disclaimer.
  34  * 2. Redistributions in binary form must reproduce the above copyright
  35  *    notice, this list of conditions and the following disclaimer in the
  36  *    documentation and/or other materials provided with the distribution.
  37  * 3. All advertising materials mentioning features or use of this software
  38  *    must display the following acknowledgement:
  39  *      This product includes software developed by the University of
  40  *      California, Berkeley and its contributors.
  41  * 4. Neither the name of the University nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58
  59 #include <sys/types.h>
  60
  61 #include <stdio.h>
  62
  63 #include <db.h>
  64 #include "btree.h"
  65
  66 static int bt_snext __P((BTREE *, PAGE *, const DBT *, int *));
  67 static int bt_sprev __P((BTREE *, PAGE *, const DBT *, int *));
  68
  69 /*
  70  * __BT_SEARCH -- Search a btree for a key.
  71  *
  72  * Parameters:
  73  *      t:      tree to search
  74  *      key:    key to find
  75  *      exactp: pointer to exact match flag
  76  *
  77  * Returns:
  78  *      The EPG for matching record, if any, or the EPG for the location
  79  *      of the key, if it were inserted into the tree, is entered into
  80  *      the bt_cur field of the tree.  A pointer to the field is returned.
  81  */
  82 EPG *
  83 __bt_search(t, key, exactp)
  84         BTREE *t;
  85         const DBT *key;
  86         int *exactp;
  87 {
  88         PAGE *h;
  89         indx_t base, index, lim;
  90         pgno_t pg;
  91         int cmp;
  92
  93         BT_CLR(t);
  94         for (pg = P_ROOT;;) {
  95                 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
  96                         return (NULL);
  97
  98                 /* Do a binary search on the current page. */
  99                 t->bt_cur.page = h;
 100                 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
 101                         t->bt_cur.index = index = base + (lim >> 1);
 102                         if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) {
 103                                 if (h->flags & P_BLEAF) {
 104                                         *exactp = 1;
 105                                         return (&t->bt_cur);
 106                                 }
 107                                 goto next;
 108                         }
 109                         if (cmp > 0) {
 110                                 base = index + 1;
 111                                 --lim;
 112                         }
 113                 }
 114
 115                 /*
 116                  * If it's a leaf page, and duplicates aren't allowed, we're
 117                  * done.  If duplicates are allowed, it's possible that there
 118                  * were duplicate keys on duplicate pages, and they were later
 119                  * deleted, so we could be on a page with no matches while
 120                  * there are matches on other pages.  If we're at the start or
 121                  * end of a page, check on both sides.
 122                  */
 123                 if (h->flags & P_BLEAF) {
 124                         t->bt_cur.index = base;
 125                         *exactp = 0;
 126                         if (!ISSET(t, B_NODUPS)) {
 127                                 if (base == 0 &&
 128                                     bt_sprev(t, h, key, exactp))
 129                                         return (&t->bt_cur);
 130                                 if (base == NEXTINDEX(h) &&
 131                                     bt_snext(t, h, key, exactp))
 132                                         return (&t->bt_cur);
 133                         }
 134                         return (&t->bt_cur);
 135                 }
 136
 137                 /*
 138                  * No match found.  Base is the smallest index greater than
 139                  * key and may be zero or a last + 1 index.  If it's non-zero,
 140                  * decrement by one, and record the internal page which should
 141                  * be a parent page for the key.  If a split later occurs, the
 142                  * inserted page will be to the right of the saved page.
 143                  */
 144                 index = base ? base - 1 : base;
 145
 146 next:           if (__bt_push(t, h->pgno, index) == RET_ERROR)
 147                         return (NULL);
 148                 pg = GETBINTERNAL(h, index)->pgno;
 149                 mpool_put(t->bt_mp, h, 0);
 150         }
 151 }
 152
 153 /*
 154  * BT_SNEXT -- Check for an exact match after the key.
 155  *
 156  * Parameters:
 157  *      t:      tree to search
 158  *      h:      current page.
 159  *      key:    key to find
 160  *      exactp: pointer to exact match flag
 161  *
 162  * Returns:
 163  *      If an exact match found.
 164  */
 165 static int
 166 bt_snext(t, h, key, exactp)
 167         BTREE *t;
 168         PAGE *h;
 169         const DBT *key;
 170         int *exactp;
 171 {
 172         EPG e;
 173         PAGE *tp;
 174         pgno_t pg;
 175
 176         /* Skip until reach the end of the tree or a key. */
 177         for (pg = h->nextpg; pg != P_INVALID;) {
 178                 if ((tp = mpool_get(t->bt_mp, pg, 0)) == NULL) {
 179                         mpool_put(t->bt_mp, h, 0);
 180                         return (NULL);
 181                 }
 182                 if (NEXTINDEX(tp) != 0)
 183                         break;
 184                 pg = tp->prevpg;
 185                 mpool_put(t->bt_mp, tp, 0);
 186         }
 187         /*
 188          * The key is either an exact match, or not as good as
 189          * the one we already have.
 190          */
 191         if (pg != P_INVALID) {
 192                 e.page = tp;
 193                 e.index = NEXTINDEX(tp) - 1;
 194                 if (__bt_cmp(t, key, &e) == 0) {
 195                         mpool_put(t->bt_mp, h, 0);
 196                         t->bt_cur = e;
 197                         *exactp = 1;
 198                         return (1);
 199                 }
 200         }
 201         return (0);
 202 }
 203
 204 /*
 205  * BT_SPREV -- Check for an exact match before the key.
 206  *
 207  * Parameters:
 208  *      t:      tree to search
 209  *      h:      current page.
 210  *      key:    key to find
 211  *      exactp: pointer to exact match flag
 212  *
 213  * Returns:
 214  *      If an exact match found.
 215  */
 216 static int
 217 bt_sprev(t, h, key, exactp)
 218         BTREE *t;
 219         PAGE *h;
 220         const DBT *key;
 221         int *exactp;
 222 {
 223         EPG e;
 224         PAGE *tp;
 225         pgno_t pg;
 226
 227         /* Skip until reach the beginning of the tree or a key. */
 228         for (pg = h->prevpg; pg != P_INVALID;) {
 229                 if ((tp = mpool_get(t->bt_mp, pg, 0)) == NULL) {
 230                         mpool_put(t->bt_mp, h, 0);
 231                         return (NULL);
 232                 }
 233                 if (NEXTINDEX(tp) != 0)
 234                         break;
 235                 pg = tp->prevpg;
 236                 mpool_put(t->bt_mp, tp, 0);
 237         }
 238         /*
 239          * The key is either an exact match, or not as good as
 240          * the one we already have.
 241          */
 242         if (pg != P_INVALID) {
 243                 e.page = tp;
 244                 e.index = NEXTINDEX(tp) - 1;
 245                 if (__bt_cmp(t, key, &e) == 0) {
 246                         mpool_put(t->bt_mp, h, 0);
 247                         t->bt_cur = e;
 248                         *exactp = 1;
 249                         return (1);
 250                 }
 251         }
 252         return (0);
 253 }