1 /* $NetBSD: bt_search.c,v 1.13 2003/08/07 16:42:41 agc 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. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 #if defined(LIBC_SCCS) && !defined(lint) 37 #if 0 38 static char sccsid[] = "@(#)bt_search.c 8.8 (Berkeley) 7/31/94"; 39 #else 40 __RCSID("$NetBSD: bt_search.c,v 1.13 2003/08/07 16:42:41 agc Exp $"); 41 #endif 42 #endif /* LIBC_SCCS and not lint */ 43 44 #include "namespace.h" 45 #include <sys/types.h> 46 47 #include <stdio.h> 48 49 #include <db.h> 50 #include "btree.h" 51 52 static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *)); 53 static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *)); 54 55 /* 56 * __bt_search -- 57 * Search a btree for a key. 58 * 59 * Parameters: 60 * t: tree to search 61 * key: key to find 62 * exactp: pointer to exact match flag 63 * 64 * Returns: 65 * The EPG for matching record, if any, or the EPG for the location 66 * of the key, if it were inserted into the tree, is entered into 67 * the bt_cur field of the tree. A pointer to the field is returned. 68 */ 69 EPG * 70 __bt_search(t, key, exactp) 71 BTREE *t; 72 const DBT *key; 73 int *exactp; 74 { 75 PAGE *h; 76 indx_t base, idx, lim; 77 pgno_t pg; 78 int cmp; 79 80 BT_CLR(t); 81 for (pg = P_ROOT;;) { 82 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 83 return (NULL); 84 85 /* Do a binary search on the current page. */ 86 t->bt_cur.page = h; 87 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 88 t->bt_cur.index = idx = base + ((u_int32_t)lim >> 1); 89 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 90 if (h->flags & P_BLEAF) { 91 *exactp = 1; 92 return (&t->bt_cur); 93 } 94 goto next; 95 } 96 if (cmp > 0) { 97 base = idx + 1; 98 --lim; 99 } 100 } 101 102 /* 103 * If it's a leaf page, we're almost done. If no duplicates 104 * are allowed, or we have an exact match, we're done. Else, 105 * it's possible that there were matching keys on this page, 106 * which later deleted, and we're on a page with no matches 107 * while there are matches on other pages. If at the start or 108 * end of a page, check the adjacent page. 109 */ 110 if (h->flags & P_BLEAF) { 111 if (!F_ISSET(t, B_NODUPS)) { 112 if (base == 0 && 113 h->prevpg != P_INVALID && 114 __bt_sprev(t, h, key, exactp)) 115 return (&t->bt_cur); 116 if (base == NEXTINDEX(h) && 117 h->nextpg != P_INVALID && 118 __bt_snext(t, h, key, exactp)) 119 return (&t->bt_cur); 120 } 121 *exactp = 0; 122 t->bt_cur.index = base; 123 return (&t->bt_cur); 124 } 125 126 /* 127 * No match found. Base is the smallest index greater than 128 * key and may be zero or a last + 1 index. If it's non-zero, 129 * decrement by one, and record the internal page which should 130 * be a parent page for the key. If a split later occurs, the 131 * inserted page will be to the right of the saved page. 132 */ 133 idx = base ? base - 1 : base; 134 135 next: BT_PUSH(t, h->pgno, idx); 136 pg = GETBINTERNAL(h, idx)->pgno; 137 mpool_put(t->bt_mp, h, 0); 138 } 139 } 140 141 /* 142 * __bt_snext -- 143 * Check for an exact match after the key. 144 * 145 * Parameters: 146 * t: tree 147 * h: current page 148 * key: key 149 * exactp: pointer to exact match flag 150 * 151 * Returns: 152 * If an exact match found. 153 */ 154 static int 155 __bt_snext(t, h, key, exactp) 156 BTREE *t; 157 PAGE *h; 158 const DBT *key; 159 int *exactp; 160 { 161 EPG e; 162 163 /* 164 * Get the next page. The key is either an exact 165 * match, or not as good as the one we already have. 166 */ 167 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 168 return (0); 169 e.index = 0; 170 if (__bt_cmp(t, key, &e) == 0) { 171 mpool_put(t->bt_mp, h, 0); 172 t->bt_cur = e; 173 *exactp = 1; 174 return (1); 175 } 176 mpool_put(t->bt_mp, e.page, 0); 177 return (0); 178 } 179 180 /* 181 * __bt_sprev -- 182 * Check for an exact match before the key. 183 * 184 * Parameters: 185 * t: tree 186 * h: current page 187 * key: key 188 * exactp: pointer to exact match flag 189 * 190 * Returns: 191 * If an exact match found. 192 */ 193 static int 194 __bt_sprev(t, h, key, exactp) 195 BTREE *t; 196 PAGE *h; 197 const DBT *key; 198 int *exactp; 199 { 200 EPG e; 201 202 /* 203 * Get the previous page. The key is either an exact 204 * match, or not as good as the one we already have. 205 */ 206 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 207 return (0); 208 e.index = NEXTINDEX(e.page) - 1; 209 if (__bt_cmp(t, key, &e) == 0) { 210 mpool_put(t->bt_mp, h, 0); 211 t->bt_cur = e; 212 *exactp = 1; 213 return (1); 214 } 215 mpool_put(t->bt_mp, e.page, 0); 216 return (0); 217 } 218