usr/src/lib/libc/db/btree/bt_search.c

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Mike Olson.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)bt_search.c 5.6 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <db.h>
#include <stdio.h>

#include "btree.h"

/*
 * __BT_SEARCH -- Search a btree for a key.
 *
 * Parameters:
 *      t:      tree to search
 *      key:    key to find
 *      exactp: pointer to exact match flag
 *
 * Returns:
 *      EPG for matching record, if any, or the EPG for the location of the
 *      key, if it were inserted into the tree.
 *
 * Warnings:
 *      The EPG returned is in static memory, and will be overwritten by the
 *      next search of any kind in any tree.
 */
EPG *
__bt_search(t, key, exactp)
        BTREE *t;
        const DBT *key;
        int *exactp;
{
        register index_t index;
        register int base, cmp, lim;
        register PAGE *h;
        pgno_t pg;
        static EPG e;

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

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

                /* If it's a leaf page, we're done. */
                if (h->flags & P_BLEAF) {
                        e.index = base;
                        *exactp = 0;
                        return (&e);
                }

                /*
                 * 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);
        }
}