bt_search.c

Go to the documentation of this file.

/*-
 * Copyright (c) 1990, 1993, 1994
 * The Regents of the University of California. All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Mike Olson.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 * must display the following acknowledgement:
 * This product includes software developed by the University of
 * California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 * may be used to endorse or promote products derived from this software
 * without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)bt_search.c 8.8 (Berkeley) 7/31/94";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <stdio.h>

#include "../include/db.h"
#include "btree.h"

static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *));
static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *));

/*
 * __bt_search --
 * Search a btree for a key.
 *
 * Parameters:
 * t: tree to search
 * key: key to find
 * exactp: pointer to exact match flag
 *
 * Returns:
 * The EPG for matching record, if any, or the EPG for the location
 * of the key, if it were inserted into the tree, is entered into
 * the bt_cur field of the tree. A pointer to the field is returned.
 */
EPG *
__bt_search(t, key, exactp)
 BTREE *t;
 const DBT *key;
 int *exactp;
{
 PAGE *h;
 indx_t base, index, lim;
 pgno_t pg;
 int cmp;

 BT_CLR(t);
 for (pg = P_ROOT;;) {
 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
 return (NULL);

 /* Do a binary search on the current page. */
 t->bt_cur.page = h;
 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
 t->bt_cur.index = index = base + (lim >> 1);
 if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) {
 if (h->flags & P_BLEAF) {
 *exactp = 1;
 return (&t->bt_cur);
 }
 goto next;
 }
 if (cmp > 0) {
 base = index + 1;
 --lim;
 }
 }

 /*
 * If it's a leaf page, we're almost done. If no duplicates
 * are allowed, or we have an exact match, we're done. Else,
 * it's possible that there were matching keys on this page,
 * which later deleted, and we're on a page with no matches
 * while there are matches on other pages. If at the start or
 * end of a page, check the adjacent page.
 */
 if (h->flags & P_BLEAF) {
 if (!F_ISSET(t, B_NODUPS)) {
 if (base == 0 &&
 h->prevpg != P_INVALID &&
 __bt_sprev(t, h, key, exactp))
 return (&t->bt_cur);
 if (base == NEXTINDEX(h) &&
 h->nextpg != P_INVALID &&
 __bt_snext(t, h, key, exactp))
 return (&t->bt_cur);
 }
 *exactp = 0;
 t->bt_cur.index = base;
 return (&t->bt_cur);
 }

 /*
 * No match found. Base is the smallest index greater than
 * key and may be zero or a last + 1 index. If it's non-zero,
 * decrement by one, and record the internal page which should
 * be a parent page for the key. If a split later occurs, the
 * inserted page will be to the right of the saved page.
 */
 index = base ? base - 1 : base;

next: BT_PUSH(t, h->pgno, index);
 pg = GETBINTERNAL(h, index)->pgno;
 mpool_put(t->bt_mp, h, 0);
 }
}

/*
 * __bt_snext --
 * Check for an exact match after the key.
 *
 * Parameters:
 * t: tree
 * h: current page
 * key: key
 * exactp: pointer to exact match flag
 *
 * Returns:
 * If an exact match found.
 */
static int
__bt_snext(t, h, key, exactp)
 BTREE *t;
 PAGE *h;
 const DBT *key;
 int *exactp;
{
 EPG e;

 /*
 * Get the next page. The key is either an exact
 * match, or not as good as the one we already have.
 */
 if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
 return (0);
 e.index = 0;
 if (__bt_cmp(t, key, &e) == 0) {
 mpool_put(t->bt_mp, h, 0);
 t->bt_cur = e;
 *exactp = 1;
 return (1);
 }
 mpool_put(t->bt_mp, e.page, 0);
 return (0);
}

/*
 * __bt_sprev --
 * Check for an exact match before the key.
 *
 * Parameters:
 * t: tree
 * h: current page
 * key: key
 * exactp: pointer to exact match flag
 *
 * Returns:
 * If an exact match found.
 */
static int
__bt_sprev(t, h, key, exactp)
 BTREE *t;
 PAGE *h;
 const DBT *key;
 int *exactp;
{
 EPG e;

 /*
 * Get the previous page. The key is either an exact
 * match, or not as good as the one we already have.
 */
 if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
 return (0);
 e.index = NEXTINDEX(e.page) - 1;
 if (__bt_cmp(t, key, &e) == 0) {
 mpool_put(t->bt_mp, h, 0);
 t->bt_cur = e;
 *exactp = 1;
 return (1);
 }
 mpool_put(t->bt_mp, e.page, 0);
 return (0);
}