1 /*- 2 * Copyright (c) 1990, 1993, 1994 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Mike Olson. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * @(#)bt_search.c 8.8 (Berkeley) 7/31/94 33 * $FreeBSD: head/lib/libc/db/btree/bt_search.c 189292 2009-03-03 02:16:12Z delphij $ 34 */ 35 36 #include <sys/types.h> 37 38 #include <stdio.h> 39 40 #include <db.h> 41 #include "btree.h" 42 43 static int __bt_snext(BTREE *, PAGE *, const DBT *, int *); 44 static int __bt_sprev(BTREE *, PAGE *, const DBT *, int *); 45 46 /* 47 * __bt_search -- 48 * Search a btree for a key. 49 * 50 * Parameters: 51 * t: tree to search 52 * key: key to find 53 * exactp: pointer to exact match flag 54 * 55 * Returns: 56 * The EPG for matching record, if any, or the EPG for the location 57 * of the key, if it were inserted into the tree, is entered into 58 * the bt_cur field of the tree. A pointer to the field is returned. 59 */ 60 EPG * 61 __bt_search(BTREE *t, const DBT *key, int *exactp) 62 { 63 PAGE *h; 64 indx_t base, idx, lim; 65 pgno_t pg; 66 int cmp; 67 68 BT_CLR(t); 69 for (pg = P_ROOT;;) { 70 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 71 return (NULL); 72 73 /* Do a binary search on the current page. */ 74 t->bt_cur.page = h; 75 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 76 t->bt_cur.index = idx = base + (lim >> 1); 77 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 78 if (h->flags & P_BLEAF) { 79 *exactp = 1; 80 return (&t->bt_cur); 81 } 82 goto next; 83 } 84 if (cmp > 0) { 85 base = idx + 1; 86 --lim; 87 } 88 } 89 90 /* 91 * If it's a leaf page, we're almost done. If no duplicates 92 * are allowed, or we have an exact match, we're done. Else, 93 * it's possible that there were matching keys on this page, 94 * which later deleted, and we're on a page with no matches 95 * while there are matches on other pages. If at the start or 96 * end of a page, check the adjacent page. 97 */ 98 if (h->flags & P_BLEAF) { 99 if (!F_ISSET(t, B_NODUPS)) { 100 if (base == 0 && 101 h->prevpg != P_INVALID && 102 __bt_sprev(t, h, key, exactp)) 103 return (&t->bt_cur); 104 if (base == NEXTINDEX(h) && 105 h->nextpg != P_INVALID && 106 __bt_snext(t, h, key, exactp)) 107 return (&t->bt_cur); 108 } 109 *exactp = 0; 110 t->bt_cur.index = base; 111 return (&t->bt_cur); 112 } 113 114 /* 115 * No match found. Base is the smallest index greater than 116 * key and may be zero or a last + 1 index. If it's non-zero, 117 * decrement by one, and record the internal page which should 118 * be a parent page for the key. If a split later occurs, the 119 * inserted page will be to the right of the saved page. 120 */ 121 idx = base ? base - 1 : base; 122 123 next: BT_PUSH(t, h->pgno, idx); 124 pg = GETBINTERNAL(h, idx)->pgno; 125 mpool_put(t->bt_mp, h, 0); 126 } 127 } 128 129 /* 130 * __bt_snext -- 131 * Check for an exact match after the key. 132 * 133 * Parameters: 134 * t: tree 135 * h: current page 136 * key: key 137 * exactp: pointer to exact match flag 138 * 139 * Returns: 140 * If an exact match found. 141 */ 142 static int 143 __bt_snext(BTREE *t, PAGE *h, const DBT *key, int *exactp) 144 { 145 EPG e; 146 147 /* 148 * Get the next page. The key is either an exact 149 * match, or not as good as the one we already have. 150 */ 151 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 152 return (0); 153 e.index = 0; 154 if (__bt_cmp(t, key, &e) == 0) { 155 mpool_put(t->bt_mp, h, 0); 156 t->bt_cur = e; 157 *exactp = 1; 158 return (1); 159 } 160 mpool_put(t->bt_mp, e.page, 0); 161 return (0); 162 } 163 164 /* 165 * __bt_sprev -- 166 * Check for an exact match before the key. 167 * 168 * Parameters: 169 * t: tree 170 * h: current page 171 * key: key 172 * exactp: pointer to exact match flag 173 * 174 * Returns: 175 * If an exact match found. 176 */ 177 static int 178 __bt_sprev(BTREE *t, PAGE *h, const DBT *key, int *exactp) 179 { 180 EPG e; 181 182 /* 183 * Get the previous page. The key is either an exact 184 * match, or not as good as the one we already have. 185 */ 186 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 187 return (0); 188 e.index = NEXTINDEX(e.page) - 1; 189 if (__bt_cmp(t, key, &e) == 0) { 190 mpool_put(t->bt_mp, h, 0); 191 t->bt_cur = e; 192 *exactp = 1; 193 return (1); 194 } 195 mpool_put(t->bt_mp, e.page, 0); 196 return (0); 197 } 198