1 /* $NetBSD: bt_search.c,v 1.16 2008/09/10 17:52:35 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 __RCSID("$NetBSD: bt_search.c,v 1.16 2008/09/10 17:52:35 joerg Exp $"); 37 38 #include "namespace.h" 39 #include <sys/types.h> 40 41 #include <assert.h> 42 #include <stdio.h> 43 44 #include <db.h> 45 #include "btree.h" 46 47 static int __bt_snext(BTREE *, PAGE *, const DBT *, int *); 48 static int __bt_sprev(BTREE *, PAGE *, const DBT *, int *); 49 50 /* 51 * __bt_search -- 52 * Search a btree for a key. 53 * 54 * Parameters: 55 * t: tree to search 56 * key: key to find 57 * exactp: pointer to exact match flag 58 * 59 * Returns: 60 * The EPG for matching record, if any, or the EPG for the location 61 * of the key, if it were inserted into the tree, is entered into 62 * the bt_cur field of the tree. A pointer to the field is returned. 63 */ 64 EPG * 65 __bt_search(BTREE *t, const DBT *key, int *exactp) 66 { 67 PAGE *h; 68 indx_t base, idx, lim; 69 pgno_t pg; 70 int cmp; 71 72 BT_CLR(t); 73 for (pg = P_ROOT;;) { 74 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 75 return (NULL); 76 77 /* Do a binary search on the current page. */ 78 t->bt_cur.page = h; 79 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 80 t->bt_cur.index = idx = base + ((uint32_t)lim >> 1); 81 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 82 if (h->flags & P_BLEAF) { 83 *exactp = 1; 84 return (&t->bt_cur); 85 } 86 goto next; 87 } 88 if (cmp > 0) { 89 base = idx + 1; 90 --lim; 91 } 92 } 93 94 /* 95 * If it's a leaf page, we're almost done. If no duplicates 96 * are allowed, or we have an exact match, we're done. Else, 97 * it's possible that there were matching keys on this page, 98 * which later deleted, and we're on a page with no matches 99 * while there are matches on other pages. If at the start or 100 * end of a page, check the adjacent page. 101 */ 102 if (h->flags & P_BLEAF) { 103 if (!F_ISSET(t, B_NODUPS)) { 104 if (base == 0 && 105 h->prevpg != P_INVALID && 106 __bt_sprev(t, h, key, exactp)) 107 return (&t->bt_cur); 108 if (base == NEXTINDEX(h) && 109 h->nextpg != P_INVALID && 110 __bt_snext(t, h, key, exactp)) 111 return (&t->bt_cur); 112 } 113 *exactp = 0; 114 t->bt_cur.index = base; 115 return (&t->bt_cur); 116 } 117 118 /* 119 * No match found. Base is the smallest index greater than 120 * key and may be zero or a last + 1 index. If it's non-zero, 121 * decrement by one, and record the internal page which should 122 * be a parent page for the key. If a split later occurs, the 123 * inserted page will be to the right of the saved page. 124 */ 125 idx = base ? base - 1 : base; 126 127 next: BT_PUSH(t, h->pgno, idx); 128 pg = GETBINTERNAL(h, idx)->pgno; 129 mpool_put(t->bt_mp, h, 0); 130 } 131 } 132 133 /* 134 * __bt_snext -- 135 * Check for an exact match after the key. 136 * 137 * Parameters: 138 * t: tree 139 * h: current page 140 * key: key 141 * exactp: pointer to exact match flag 142 * 143 * Returns: 144 * If an exact match found. 145 */ 146 static int 147 __bt_snext(BTREE *t, PAGE *h, const DBT *key, int *exactp) 148 { 149 EPG e; 150 151 /* 152 * Get the next page. The key is either an exact 153 * match, or not as good as the one we already have. 154 */ 155 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 156 return (0); 157 e.index = 0; 158 if (__bt_cmp(t, key, &e) == 0) { 159 mpool_put(t->bt_mp, h, 0); 160 t->bt_cur = e; 161 *exactp = 1; 162 return (1); 163 } 164 mpool_put(t->bt_mp, e.page, 0); 165 return (0); 166 } 167 168 /* 169 * __bt_sprev -- 170 * Check for an exact match before the key. 171 * 172 * Parameters: 173 * t: tree 174 * h: current page 175 * key: key 176 * exactp: pointer to exact match flag 177 * 178 * Returns: 179 * If an exact match found. 180 */ 181 static int 182 __bt_sprev(BTREE *t, PAGE *h, const DBT *key, int *exactp) 183 { 184 EPG e; 185 186 /* 187 * Get the previous page. The key is either an exact 188 * match, or not as good as the one we already have. 189 */ 190 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 191 return (0); 192 e.index = NEXTINDEX(e.page) - 1; 193 if (__bt_cmp(t, key, &e) == 0) { 194 mpool_put(t->bt_mp, h, 0); 195 t->bt_cur = e; 196 *exactp = 1; 197 return (1); 198 } 199 mpool_put(t->bt_mp, e.page, 0); 200 return (0); 201 } 202