## root/libdb/bt_search.c(62.html)

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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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