root/libdb/bt_search.c

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DEFINITIONS

This source file includes following definitions.
  1. __bt_search
  2. __bt_snext
  3. __bt_sprev

/*-
 * 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. 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 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <sys/types.h>

#include <stdio.h>

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

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

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