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 37 #if defined(LIBC_SCCS) && !defined(lint) 38 static char sccsid[] = "@(#)bt_search.c 8.8 (Berkeley) 7/31/94"; 39 #endif /* LIBC_SCCS and not lint */ 40 41 #include <sys/types.h> 42 43 #include <stdio.h> 44 45 #include <db.h> 46 #include "btree.h" 47 48 static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *)); 49 static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *)); 50 51 /* 52 * __bt_search -- 53 * Search a btree for a key. 54 * 55 * Parameters: 56 * t: tree to search 57 * key: key to find 58 * exactp: pointer to exact match flag 59 * 60 * Returns: 61 * The EPG for matching record, if any, or the EPG for the location 62 * of the key, if it were inserted into the tree, is entered into 63 * the bt_cur field of the tree. A pointer to the field is returned. 64 */ 65 EPG * 66 __bt_search(t, key, exactp) 67 BTREE *t; 68 const DBT *key; 69 int *exactp; 70 { 71 PAGE *h; 72 indx_t base, index, lim; 73 pgno_t pg; 74 int cmp; 75 76 BT_CLR(t); 77 for (pg = P_ROOT;;) { 78 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 79 return (NULL); 80 81 /* Do a binary search on the current page. */ 82 t->bt_cur.page = h; 83 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 84 t->bt_cur.index = index = base + (lim >> 1); 85 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) { 86 if (h->flags & P_BLEAF) { 87 *exactp = 1; 88 return (&t->bt_cur); 89 } 90 goto next; 91 } 92 if (cmp > 0) { 93 base = index + 1; 94 --lim; 95 } 96 } 97 98 /* 99 * If it's a leaf page, we're almost done. If no duplicates 100 * are allowed, or we have an exact match, we're done. Else, 101 * it's possible that there were matching keys on this page, 102 * which later deleted, and we're on a page with no matches 103 * while there are matches on other pages. If at the start or 104 * end of a page, check the adjacent page. 105 */ 106 if (h->flags & P_BLEAF) { 107 if (!F_ISSET(t, B_NODUPS)) { 108 if (base == 0 && 109 h->prevpg != P_INVALID && 110 __bt_sprev(t, h, key, exactp)) 111 return (&t->bt_cur); 112 if (base == NEXTINDEX(h) && 113 h->nextpg != P_INVALID && 114 __bt_snext(t, h, key, exactp)) 115 return (&t->bt_cur); 116 } 117 *exactp = 0; 118 t->bt_cur.index = base; 119 return (&t->bt_cur); 120 } 121 122 /* 123 * No match found. Base is the smallest index greater than 124 * key and may be zero or a last + 1 index. If it's non-zero, 125 * decrement by one, and record the internal page which should 126 * be a parent page for the key. If a split later occurs, the 127 * inserted page will be to the right of the saved page. 128 */ 129 index = base ? base - 1 : base; 130 131 next: BT_PUSH(t, h->pgno, index); 132 pg = GETBINTERNAL(h, index)->pgno; 133 mpool_put(t->bt_mp, h, 0); 134 } 135 } 136 137 /* 138 * __bt_snext -- 139 * Check for an exact match after the key. 140 * 141 * Parameters: 142 * t: tree 143 * h: current page 144 * key: key 145 * exactp: pointer to exact match flag 146 * 147 * Returns: 148 * If an exact match found. 149 */ 150 static int 151 __bt_snext(t, h, key, exactp) 152 BTREE *t; 153 PAGE *h; 154 const DBT *key; 155 int *exactp; 156 { 157 EPG e; 158 159 /* 160 * Get the next page. The key is either an exact 161 * match, or not as good as the one we already have. 162 */ 163 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) 164 return (0); 165 e.index = 0; 166 if (__bt_cmp(t, key, &e) == 0) { 167 mpool_put(t->bt_mp, h, 0); 168 t->bt_cur = e; 169 *exactp = 1; 170 return (1); 171 } 172 mpool_put(t->bt_mp, e.page, 0); 173 return (0); 174 } 175 176 /* 177 * __bt_sprev -- 178 * Check for an exact match before the key. 179 * 180 * Parameters: 181 * t: tree 182 * h: current page 183 * key: key 184 * exactp: pointer to exact match flag 185 * 186 * Returns: 187 * If an exact match found. 188 */ 189 static int 190 __bt_sprev(t, h, key, exactp) 191 BTREE *t; 192 PAGE *h; 193 const DBT *key; 194 int *exactp; 195 { 196 EPG e; 197 198 /* 199 * Get the previous page. The key is either an exact 200 * match, or not as good as the one we already have. 201 */ 202 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) 203 return (0); 204 e.index = NEXTINDEX(e.page) - 1; 205 if (__bt_cmp(t, key, &e) == 0) { 206 mpool_put(t->bt_mp, h, 0); 207 t->bt_cur = e; 208 *exactp = 1; 209 return (1); 210 } 211 mpool_put(t->bt_mp, e.page, 0); 212 return (0); 213 } 214