bt_search.c

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/*-
 * 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);
}