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 * $DragonFly: src/lib/libc/db/btree/bt_search.c,v 1.5 2005/09/19 09:20:37 asmodai Exp $ 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(t, key, exactp) 62 BTREE *t; 63 const DBT *key; 64 int *exactp; 65 { 66 PAGE *h; 67 indx_t base, index, lim; 68 pgno_t pg; 69 int cmp; 70 71 BT_CLR(t); 72 for (pg = P_ROOT;;) { 73 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 74 return (NULL); 75 76 /* Do a binary search on the current page. */ 77 t->bt_cur.page = h; 78 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 79 t->bt_cur.index = index = base + (lim >> 1); 80 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 81 if (h->flags & P_BLEAF) { 82 *exactp = 1; 83 return (&t->bt_cur); 84 } 85 goto next; 86 } 87 if (cmp > 0) { 88 base = index + 1; 89 --lim; 90 } 91 } 92 93 /* 94 * If it's a leaf page, we're almost done. If no duplicates 95 * are allowed, or we have an exact match, we're done. Else, 96 * it's possible that there were matching keys on this page, 97 * which later deleted, and we're on a page with no matches 98 * while there are matches on other pages. If at the start or 99 * end of a page, check the adjacent page. 100 */ 101 if (h->flags & P_BLEAF) { 102 if (!F_ISSET(t, B_NODUPS)) { 103 if (base == 0 && 104 h->prevpg != P_INVALID && 105 __bt_sprev(t, h, key, exactp)) 106 return (&t->bt_cur); 107 if (base == NEXTINDEX(h) && 108 h->nextpg != P_INVALID && 109 __bt_snext(t, h, key, exactp)) 110 return (&t->bt_cur); 111 } 112 *exactp = 0; 113 t->bt_cur.index = base; 114 return (&t->bt_cur); 115 } 116 117 /* 118 * No match found. Base is the smallest index greater than 119 * key and may be zero or a last + 1 index. If it's non-zero, 120 * decrement by one, and record the internal page which should 121 * be a parent page for the key. If a split later occurs, the 122 * inserted page will be to the right of the saved page. 123 */ 124 index = base ? base - 1 : base; 125 126 next: BT_PUSH(t, h->pgno, index); 127 pg = GETBINTERNAL(h, index)->pgno; 128 mpool_put(t->bt_mp, h, 0); 129 } 130 } 131 132 /* 133 * __bt_snext -- 134 * Check for an exact match after the key. 135 * 136 * Parameters: 137 * t: tree 138 * h: current page 139 * key: key 140 * exactp: pointer to exact match flag 141 * 142 * Returns: 143 * If an exact match found. 144 */ 145 static int 146 __bt_snext(t, h, key, exactp) 147 BTREE *t; 148 PAGE *h; 149 const DBT *key; 150 int *exactp; 151 { 152 EPG e; 153 154 /* 155 * Get the next page. The key is either an exact 156 * match, or not as good as the one we already have. 157 */ 158 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 159 return (0); 160 e.index = 0; 161 if (__bt_cmp(t, key, &e) == 0) { 162 mpool_put(t->bt_mp, h, 0); 163 t->bt_cur = e; 164 *exactp = 1; 165 return (1); 166 } 167 mpool_put(t->bt_mp, e.page, 0); 168 return (0); 169 } 170 171 /* 172 * __bt_sprev -- 173 * Check for an exact match before the key. 174 * 175 * Parameters: 176 * t: tree 177 * h: current page 178 * key: key 179 * exactp: pointer to exact match flag 180 * 181 * Returns: 182 * If an exact match found. 183 */ 184 static int 185 __bt_sprev(t, h, key, exactp) 186 BTREE *t; 187 PAGE *h; 188 const DBT *key; 189 int *exactp; 190 { 191 EPG e; 192 193 /* 194 * Get the previous page. The key is either an exact 195 * match, or not as good as the one we already have. 196 */ 197 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 198 return (0); 199 e.index = NEXTINDEX(e.page) - 1; 200 if (__bt_cmp(t, key, &e) == 0) { 201 mpool_put(t->bt_mp, h, 0); 202 t->bt_cur = e; 203 *exactp = 1; 204 return (1); 205 } 206 mpool_put(t->bt_mp, e.page, 0); 207 return (0); 208 } 209