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. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)bt_search.c 8.8 (Berkeley) 7/31/94 37 */ 38 39 #include <sys/types.h> 40 41 #include <stdio.h> 42 43 #include <db.h> 44 #include "btree.h" 45 46 static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *)); 47 static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *)); 48 49 /* 50 * __bt_search -- 51 * Search a btree for a key. 52 * 53 * Parameters: 54 * t: tree to search 55 * key: key to find 56 * exactp: pointer to exact match flag 57 * 58 * Returns: 59 * The EPG for matching record, if any, or the EPG for the location 60 * of the key, if it were inserted into the tree, is entered into 61 * the bt_cur field of the tree. A pointer to the field is returned. 62 */ 63 EPG * 64 __bt_search(t, key, exactp) 65 BTREE *t; 66 const DBT *key; 67 int *exactp; 68 { 69 PAGE *h; 70 indx_t base, index, lim; 71 pgno_t pg; 72 int cmp; 73 74 BT_CLR(t); 75 for (pg = P_ROOT;;) { 76 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 77 return (NULL); 78 79 /* Do a binary search on the current page. */ 80 t->bt_cur.page = h; 81 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 82 t->bt_cur.index = index = base + (lim >> 1); 83 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 84 if (h->flags & P_BLEAF) { 85 *exactp = 1; 86 return (&t->bt_cur); 87 } 88 goto next; 89 } 90 if (cmp > 0) { 91 base = index + 1; 92 --lim; 93 } 94 } 95 96 /* 97 * If it's a leaf page, we're almost done. If no duplicates 98 * are allowed, or we have an exact match, we're done. Else, 99 * it's possible that there were matching keys on this page, 100 * which later deleted, and we're on a page with no matches 101 * while there are matches on other pages. If at the start or 102 * end of a page, check the adjacent page. 103 */ 104 if (h->flags & P_BLEAF) { 105 if (!F_ISSET(t, B_NODUPS)) { 106 if (base == 0 && 107 h->prevpg != P_INVALID && 108 __bt_sprev(t, h, key, exactp)) 109 return (&t->bt_cur); 110 if (base == NEXTINDEX(h) && 111 h->nextpg != P_INVALID && 112 __bt_snext(t, h, key, exactp)) 113 return (&t->bt_cur); 114 } 115 *exactp = 0; 116 t->bt_cur.index = base; 117 return (&t->bt_cur); 118 } 119 120 /* 121 * No match found. Base is the smallest index greater than 122 * key and may be zero or a last + 1 index. If it's non-zero, 123 * decrement by one, and record the internal page which should 124 * be a parent page for the key. If a split later occurs, the 125 * inserted page will be to the right of the saved page. 126 */ 127 index = base ? base - 1 : base; 128 129 next: BT_PUSH(t, h->pgno, index); 130 pg = GETBINTERNAL(h, index)->pgno; 131 mpool_put(t->bt_mp, h, 0); 132 } 133 } 134 135 /* 136 * __bt_snext -- 137 * Check for an exact match after the key. 138 * 139 * Parameters: 140 * t: tree 141 * h: current page 142 * key: key 143 * exactp: pointer to exact match flag 144 * 145 * Returns: 146 * If an exact match found. 147 */ 148 static int 149 __bt_snext(t, h, key, exactp) 150 BTREE *t; 151 PAGE *h; 152 const DBT *key; 153 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(t, h, key, exactp) 189 BTREE *t; 190 PAGE *h; 191 const DBT *key; 192 int *exactp; 193 { 194 EPG e; 195 196 /* 197 * Get the previous page. The key is either an exact 198 * match, or not as good as the one we already have. 199 */ 200 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 201 return (0); 202 e.index = NEXTINDEX(e.page) - 1; 203 if (__bt_cmp(t, key, &e) == 0) { 204 mpool_put(t->bt_mp, h, 0); 205 t->bt_cur = e; 206 *exactp = 1; 207 return (1); 208 } 209 mpool_put(t->bt_mp, e.page, 0); 210 return (0); 211 } 212