1 /* $NetBSD: bt_search.c,v 1.15 2008/08/26 21:18:38 joerg 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 1.15 2008/08/26 21:18:38 joerg Exp $"); 41 #endif 42 #endif /* LIBC_SCCS and not lint */ 43 44 #include "namespace.h" 45 #include <sys/types.h> 46 47 #include <assert.h> 48 #include <stdio.h> 49 50 #include <db.h> 51 #include "btree.h" 52 53 static int __bt_snext(BTREE *, PAGE *, const DBT *, int *); 54 static int __bt_sprev(BTREE *, PAGE *, const DBT *, int *); 55 56 /* 57 * __bt_search -- 58 * Search a btree for a key. 59 * 60 * Parameters: 61 * t: tree to search 62 * key: key to find 63 * exactp: pointer to exact match flag 64 * 65 * Returns: 66 * The EPG for matching record, if any, or the EPG for the location 67 * of the key, if it were inserted into the tree, is entered into 68 * the bt_cur field of the tree. A pointer to the field is returned. 69 */ 70 EPG * 71 __bt_search(BTREE *t, const DBT *key, int *exactp) 72 { 73 PAGE *h; 74 indx_t base, idx, 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 = idx = base + ((uint32_t)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 = idx + 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 idx = base ? base - 1 : base; 132 133 next: BT_PUSH(t, h->pgno, idx); 134 pg = GETBINTERNAL(h, idx)->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 */ 152 static int 153 __bt_snext(BTREE *t, PAGE *h, const DBT *key, int *exactp) 154 { 155 EPG e; 156 157 /* 158 * Get the next page. The key is either an exact 159 * match, or not as good as the one we already have. 160 */ 161 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 162 return (0); 163 e.index = 0; 164 if (__bt_cmp(t, key, &e) == 0) { 165 mpool_put(t->bt_mp, h, 0); 166 t->bt_cur = e; 167 *exactp = 1; 168 return (1); 169 } 170 mpool_put(t->bt_mp, e.page, 0); 171 return (0); 172 } 173 174 /* 175 * __bt_sprev -- 176 * Check for an exact match before the key. 177 * 178 * Parameters: 179 * t: tree 180 * h: current page 181 * key: key 182 * exactp: pointer to exact match flag 183 * 184 * Returns: 185 * If an exact match found. 186 */ 187 static int 188 __bt_sprev(BTREE *t, PAGE *h, const DBT *key, int *exactp) 189 { 190 EPG e; 191 192 /* 193 * Get the previous page. The key is either an exact 194 * match, or not as good as the one we already have. 195 */ 196 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 197 return (0); 198 e.index = NEXTINDEX(e.page) - 1; 199 if (__bt_cmp(t, key, &e) == 0) { 200 mpool_put(t->bt_mp, h, 0); 201 t->bt_cur = e; 202 *exactp = 1; 203 return (1); 204 } 205 mpool_put(t->bt_mp, e.page, 0); 206 return (0); 207 } 208