bt_search.c revision 92905
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) 38static 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: head/lib/libc/db/btree/bt_search.c 92905 2002-03-21 22:49:10Z obrien $"); 42 43#include <sys/types.h> 44 45#include <stdio.h> 46 47#include <db.h> 48#include "btree.h" 49 50static int __bt_snext(BTREE *, PAGE *, const DBT *, int *); 51static 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 */ 67EPG * 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 133next: 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 */ 152static 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 */ 191static 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} 216