1 /* $OpenBSD: bt_search.c,v 1.4 1999/02/15 05:11:23 millert 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. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 */ 38 39 #if defined(LIBC_SCCS) && !defined(lint) 40 #if 0 41 static char sccsid[] = "@(#)bt_search.c 8.8 (Berkeley) 7/31/94"; 42 #else 43 static char rcsid[] = "$OpenBSD: bt_search.c,v 1.4 1999/02/15 05:11:23 millert Exp $"; 44 #endif 45 #endif /* LIBC_SCCS and not lint */ 46 47 #include <sys/types.h> 48 49 #include <stdio.h> 50 51 #include <db.h> 52 #include "btree.h" 53 54 static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *)); 55 static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *)); 56 57 /* 58 * __bt_search -- 59 * Search a btree for a key. 60 * 61 * Parameters: 62 * t: tree to search 63 * key: key to find 64 * exactp: pointer to exact match flag 65 * 66 * Returns: 67 * The EPG for matching record, if any, or the EPG for the location 68 * of the key, if it were inserted into the tree, is entered into 69 * the bt_cur field of the tree. A pointer to the field is returned. 70 */ 71 EPG * 72 __bt_search(t, key, exactp) 73 BTREE *t; 74 const DBT *key; 75 int *exactp; 76 { 77 PAGE *h; 78 indx_t base, index, lim; 79 pgno_t pg; 80 int cmp; 81 82 BT_CLR(t); 83 for (pg = P_ROOT;;) { 84 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 85 return (NULL); 86 87 /* Do a binary search on the current page. */ 88 t->bt_cur.page = h; 89 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 90 t->bt_cur.index = index = base + (lim >> 1); 91 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 92 if (h->flags & P_BLEAF) { 93 *exactp = 1; 94 return (&t->bt_cur); 95 } 96 goto next; 97 } 98 if (cmp > 0) { 99 base = index + 1; 100 --lim; 101 } 102 } 103 104 /* 105 * If it's a leaf page, we're almost done. If no duplicates 106 * are allowed, or we have an exact match, we're done. Else, 107 * it's possible that there were matching keys on this page, 108 * which later deleted, and we're on a page with no matches 109 * while there are matches on other pages. If at the start or 110 * end of a page, check the adjacent page. 111 */ 112 if (h->flags & P_BLEAF) { 113 if (!F_ISSET(t, B_NODUPS)) { 114 if (base == 0 && 115 h->prevpg != P_INVALID && 116 __bt_sprev(t, h, key, exactp)) 117 return (&t->bt_cur); 118 if (base == NEXTINDEX(h) && 119 h->nextpg != P_INVALID && 120 __bt_snext(t, h, key, exactp)) 121 return (&t->bt_cur); 122 } 123 *exactp = 0; 124 t->bt_cur.index = base; 125 return (&t->bt_cur); 126 } 127 128 /* 129 * No match found. Base is the smallest index greater than 130 * key and may be zero or a last + 1 index. If it's non-zero, 131 * decrement by one, and record the internal page which should 132 * be a parent page for the key. If a split later occurs, the 133 * inserted page will be to the right of the saved page. 134 */ 135 index = base ? base - 1 : base; 136 137 next: BT_PUSH(t, h->pgno, index); 138 pg = GETBINTERNAL(h, index)->pgno; 139 mpool_put(t->bt_mp, h, 0); 140 } 141 } 142 143 /* 144 * __bt_snext -- 145 * Check for an exact match after the key. 146 * 147 * Parameters: 148 * t: tree 149 * h: current page 150 * key: key 151 * exactp: pointer to exact match flag 152 * 153 * Returns: 154 * If an exact match found. 155 */ 156 static int 157 __bt_snext(t, h, key, exactp) 158 BTREE *t; 159 PAGE *h; 160 const DBT *key; 161 int *exactp; 162 { 163 EPG e; 164 165 /* 166 * Get the next page. The key is either an exact 167 * match, or not as good as the one we already have. 168 */ 169 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 170 return (0); 171 e.index = 0; 172 if (__bt_cmp(t, key, &e) == 0) { 173 mpool_put(t->bt_mp, h, 0); 174 t->bt_cur = e; 175 *exactp = 1; 176 return (1); 177 } 178 mpool_put(t->bt_mp, e.page, 0); 179 return (0); 180 } 181 182 /* 183 * __bt_sprev -- 184 * Check for an exact match before the key. 185 * 186 * Parameters: 187 * t: tree 188 * h: current page 189 * key: key 190 * exactp: pointer to exact match flag 191 * 192 * Returns: 193 * If an exact match found. 194 */ 195 static int 196 __bt_sprev(t, h, key, exactp) 197 BTREE *t; 198 PAGE *h; 199 const DBT *key; 200 int *exactp; 201 { 202 EPG e; 203 204 /* 205 * Get the previous page. The key is either an exact 206 * match, or not as good as the one we already have. 207 */ 208 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 209 return (0); 210 e.index = NEXTINDEX(e.page) - 1; 211 if (__bt_cmp(t, key, &e) == 0) { 212 mpool_put(t->bt_mp, h, 0); 213 t->bt_cur = e; 214 *exactp = 1; 215 return (1); 216 } 217 mpool_put(t->bt_mp, e.page, 0); 218 return (0); 219 } 220