db/btree/bt_compare.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *  Sleepycat Software.  All rights reserved.
 */
/*
 * Copyright (c) 1990, 1993, 1994, 1995, 1996
 *  Keith Bostic.  All rights reserved.
 */
/*
 * Copyright (c) 1990, 1993, 1994, 1995
 *  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.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)bt_compare.c  10.14 (Sleepycat) 10/9/98";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <string.h>
#endif

#include "db_int.h"
#include "db_page.h"
#include "btree.h"

/*
 * __bam_cmp --
 *  Compare a key to a given record.
 *
 * PUBLIC: int __bam_cmp __P((DB *, const DBT *,
 * PUBLIC:    PAGE *, u_int32_t, int (*)(const DBT *, const DBT *)));
 */
int
__bam_cmp(dbp, dbt, h, indx, func)
    DB *dbp;
    const DBT *dbt;
    PAGE *h;
    u_int32_t indx;
    int (*func)__P((const DBT *, const DBT *));
{
    BINTERNAL *bi;
    BKEYDATA *bk;
    BOVERFLOW *bo;
    DBT pg_dbt;
    int ret;

    /*
     * Returns:
     *  < 0 if dbt is < page record
     *  = 0 if dbt is = page record
     *  > 0 if dbt is > page record
     *
     * !!!
     * We do not clear the pg_dbt DBT even though it's likely to contain
     * random bits.  That should be okay, because the app's comparison
     * routine had better not be looking at fields other than data/size.
     * We don't clear it because we go through this path a lot and it's
     * expensive.
     */
    if (TYPE(h) == P_LBTREE || TYPE(h) == P_DUPLICATE) {
        bk = GET_BKEYDATA(h, indx);
        if (B_TYPE(bk->type) == B_OVERFLOW)
            bo = (BOVERFLOW *)bk;
        else {
            pg_dbt.data = bk->data;
            pg_dbt.size = bk->len;
            return (func(dbt, &pg_dbt));
        }
    } else {
        /*
         * The following code guarantees that the left-most key on an
         * internal page at any level of the btree is less than any
         * user specified key.  This saves us from having to update the
         * leftmost key on an internal page when the user inserts a new
         * key in the tree smaller than anything we've seen before.
         */
        if (indx == 0 && h->prev_pgno == PGNO_INVALID)
            return (1);

        bi = GET_BINTERNAL(h, indx);
        if (B_TYPE(bi->type) == B_OVERFLOW)
            bo = (BOVERFLOW *)(bi->data);
        else {
            pg_dbt.data = bi->data;
            pg_dbt.size = bi->len;
            return (func(dbt, &pg_dbt));
        }
    }

    /*
     * Overflow.
     *
     * XXX
     * We ignore __db_moff() errors, because we have no way of returning
     * them.
     */
    (void) __db_moff(dbp,
        dbt, bo->pgno, bo->tlen, func == __bam_defcmp ? NULL : func, &ret);
    return (ret);
}

/*
 * __bam_defcmp --
 *  Default comparison routine.
 *
 * PUBLIC: int __bam_defcmp __P((const DBT *, const DBT *));
 */
int
__bam_defcmp(a, b)
    const DBT *a, *b;
{
    size_t len;
    u_int8_t *p1, *p2;

    /*
     * Returns:
     *  < 0 if a is < b
     *  = 0 if a is = b
     *  > 0 if a is > b
     *
     * XXX
     * If a size_t doesn't fit into a long, or if the difference between
     * any two characters doesn't fit into an int, this routine can lose.
     * What we need is a signed integral type that's guaranteed to be at
     * least as large as a size_t, and there is no such thing.
     */
    len = a->size > b->size ? b->size : a->size;
    for (p1 = a->data, p2 = b->data; len--; ++p1, ++p2)
        if (*p1 != *p2)
            return ((long)*p1 - (long)*p2);
    return ((long)a->size - (long)b->size);
}

/*
 * __bam_defpfx --
 *  Default prefix routine.
 *
 * PUBLIC: size_t __bam_defpfx __P((const DBT *, const DBT *));
 */
size_t
__bam_defpfx(a, b)
    const DBT *a, *b;
{
    size_t cnt, len;
    u_int8_t *p1, *p2;

    cnt = 1;
    len = a->size > b->size ? b->size : a->size;
    for (p1 = a->data, p2 = b->data; len--; ++p1, ++p2, ++cnt)
        if (*p1 != *p2)
            return (cnt);

    /*
     * We know that a->size must be <= b->size, or they wouldn't be
     * in this order.
     */
    return (a->size < b->size ? a->size + 1 : a->size);
}