usr/src/contrib/nvi.1.14/PORT/db.1.73/btree/bt_search.c

/*-
 * Copyright (c) 1990, 1993
 *      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 8.4 (Berkeley) 12/10/93";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <stdio.h>

#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, *n;
        indx_t index;
        pgno_t pg;
        int base, cmp, lim;

        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, and duplicates aren't allowed, we're
                 * done.  If duplicates are allowed, it's possible that there
                 * were duplicate keys on duplicate pages, and they were later
                 * deleted, so we could be on a page with no matches while
                 * there are matches on other pages.  If we're at the start or
                 * end of a page, check on both sides.
                 */
                if (h->flags & P_BLEAF) {
                        t->bt_cur.index = base;
                        *exactp = 0;
                        if (!ISSET(t, B_NODUPS)) {
                                if (base == 0 &&
                                    bt_sprev(t, h, key, exactp))
                                        return (&t->bt_cur);
                                if (base == NEXTINDEX(h) &&
                                    bt_snext(t, h, key, exactp))
                                        return (&t->bt_cur);
                        }
                        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:           if (__bt_push(t, h->pgno, index) == RET_ERROR)
                        return (NULL);
                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 to search
 *      h:      current page.
 *      key:    key to find
 *      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;
        PAGE *tp;
        pgno_t pg;

        /* Skip until reach the end of the tree or a key. */
        for (pg = h->nextpg; pg != P_INVALID;) {
                if ((tp = mpool_get(t->bt_mp, pg, 0)) == NULL) {
                        mpool_put(t->bt_mp, h, 0);
                        return (NULL);
                }
                if (NEXTINDEX(tp) != 0)
                        break;
                pg = tp->prevpg;
                mpool_put(t->bt_mp, tp, 0);
        }
        /*
         * The key is either an exact match, or not as good as
         * the one we already have.
         */
        if (pg != P_INVALID) {
                e.page = tp;
                e.index = NEXTINDEX(tp) - 1;
                if (__bt_cmp(t, key, &e) == 0) {
                        mpool_put(t->bt_mp, h, 0);
                        t->bt_cur = e;
                        *exactp = 1;
                        return (1);
                }
        }
        return (0);
}

/*
 * BT_SPREV -- Check for an exact match before the key.
 *
 * Parameters:
 *      t:      tree to search
 *      h:      current page.
 *      key:    key to find
 *      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;
        PAGE *tp;
        pgno_t pg;

        /* Skip until reach the beginning of the tree or a key. */
        for (pg = h->prevpg; pg != P_INVALID;) {
                if ((tp = mpool_get(t->bt_mp, pg, 0)) == NULL) {
                        mpool_put(t->bt_mp, h, 0);
                        return (NULL);
                }
                if (NEXTINDEX(tp) != 0)
                        break;
                pg = tp->prevpg;
                mpool_put(t->bt_mp, tp, 0);
        }
        /*
         * The key is either an exact match, or not as good as
         * the one we already have.
         */
        if (pg != P_INVALID) {
                e.page = tp;
                e.index = NEXTINDEX(tp) - 1;
                if (__bt_cmp(t, key, &e) == 0) {
                        mpool_put(t->bt_mp, h, 0);
                        t->bt_cur = e;
                        *exactp = 1;
                        return (1);
                }
        }
        return (0);
}