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 *
__bt_search(BTREE * t,const DBT * key,int * exactp)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
__bt_snext(BTREE * t,PAGE * h,const DBT * key,int * exactp)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
__bt_sprev(BTREE * t,PAGE * h,const DBT * key,int * exactp)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