1 /* $NetBSD: bt_search.c,v 1.12 2001/12/30 19:18:23 thorpej 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 #include <sys/cdefs.h> 40 #if defined(LIBC_SCCS) && !defined(lint) 41 #if 0 42 static char sccsid[] = "@(#)bt_search.c 8.8 (Berkeley) 7/31/94"; 43 #else 44 __RCSID("$NetBSD: bt_search.c,v 1.12 2001/12/30 19:18:23 thorpej Exp $"); 45 #endif 46 #endif /* LIBC_SCCS and not lint */ 47 48 #include "namespace.h" 49 #include <sys/types.h> 50 51 #include <stdio.h> 52 53 #include <db.h> 54 #include "btree.h" 55 56 static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *)); 57 static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *)); 58 59 /* 60 * __bt_search -- 61 * Search a btree for a key. 62 * 63 * Parameters: 64 * t: tree to search 65 * key: key to find 66 * exactp: pointer to exact match flag 67 * 68 * Returns: 69 * The EPG for matching record, if any, or the EPG for the location 70 * of the key, if it were inserted into the tree, is entered into 71 * the bt_cur field of the tree. A pointer to the field is returned. 72 */ 73 EPG * 74 __bt_search(t, key, exactp) 75 BTREE *t; 76 const DBT *key; 77 int *exactp; 78 { 79 PAGE *h; 80 indx_t base, idx, lim; 81 pgno_t pg; 82 int cmp; 83 84 BT_CLR(t); 85 for (pg = P_ROOT;;) { 86 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 87 return (NULL); 88 89 /* Do a binary search on the current page. */ 90 t->bt_cur.page = h; 91 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 92 t->bt_cur.index = idx = base + ((u_int32_t)lim >> 1); 93 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 94 if (h->flags & P_BLEAF) { 95 *exactp = 1; 96 return (&t->bt_cur); 97 } 98 goto next; 99 } 100 if (cmp > 0) { 101 base = idx + 1; 102 --lim; 103 } 104 } 105 106 /* 107 * If it's a leaf page, we're almost done. If no duplicates 108 * are allowed, or we have an exact match, we're done. Else, 109 * it's possible that there were matching keys on this page, 110 * which later deleted, and we're on a page with no matches 111 * while there are matches on other pages. If at the start or 112 * end of a page, check the adjacent page. 113 */ 114 if (h->flags & P_BLEAF) { 115 if (!F_ISSET(t, B_NODUPS)) { 116 if (base == 0 && 117 h->prevpg != P_INVALID && 118 __bt_sprev(t, h, key, exactp)) 119 return (&t->bt_cur); 120 if (base == NEXTINDEX(h) && 121 h->nextpg != P_INVALID && 122 __bt_snext(t, h, key, exactp)) 123 return (&t->bt_cur); 124 } 125 *exactp = 0; 126 t->bt_cur.index = base; 127 return (&t->bt_cur); 128 } 129 130 /* 131 * No match found. Base is the smallest index greater than 132 * key and may be zero or a last + 1 index. If it's non-zero, 133 * decrement by one, and record the internal page which should 134 * be a parent page for the key. If a split later occurs, the 135 * inserted page will be to the right of the saved page. 136 */ 137 idx = base ? base - 1 : base; 138 139 next: BT_PUSH(t, h->pgno, idx); 140 pg = GETBINTERNAL(h, idx)->pgno; 141 mpool_put(t->bt_mp, h, 0); 142 } 143 } 144 145 /* 146 * __bt_snext -- 147 * Check for an exact match after the key. 148 * 149 * Parameters: 150 * t: tree 151 * h: current page 152 * key: key 153 * exactp: pointer to exact match flag 154 * 155 * Returns: 156 * If an exact match found. 157 */ 158 static int 159 __bt_snext(t, h, key, exactp) 160 BTREE *t; 161 PAGE *h; 162 const DBT *key; 163 int *exactp; 164 { 165 EPG e; 166 167 /* 168 * Get the next page. The key is either an exact 169 * match, or not as good as the one we already have. 170 */ 171 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 172 return (0); 173 e.index = 0; 174 if (__bt_cmp(t, key, &e) == 0) { 175 mpool_put(t->bt_mp, h, 0); 176 t->bt_cur = e; 177 *exactp = 1; 178 return (1); 179 } 180 mpool_put(t->bt_mp, e.page, 0); 181 return (0); 182 } 183 184 /* 185 * __bt_sprev -- 186 * Check for an exact match before the key. 187 * 188 * Parameters: 189 * t: tree 190 * h: current page 191 * key: key 192 * exactp: pointer to exact match flag 193 * 194 * Returns: 195 * If an exact match found. 196 */ 197 static int 198 __bt_sprev(t, h, key, exactp) 199 BTREE *t; 200 PAGE *h; 201 const DBT *key; 202 int *exactp; 203 { 204 EPG e; 205 206 /* 207 * Get the previous page. The key is either an exact 208 * match, or not as good as the one we already have. 209 */ 210 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 211 return (0); 212 e.index = NEXTINDEX(e.page) - 1; 213 if (__bt_cmp(t, key, &e) == 0) { 214 mpool_put(t->bt_mp, h, 0); 215 t->bt_cur = e; 216 *exactp = 1; 217 return (1); 218 } 219 mpool_put(t->bt_mp, e.page, 0); 220 return (0); 221 } 222