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)
38static 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
48static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *));
49static 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 */
65EPG *
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
131next: 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 */
150static 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 */
189static 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