bt_compare.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2005
 *      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. 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.
 *
 * $Id: bt_compare.c,v 12.1 2005/06/16 20:20:13 bostic Exp $
 */

#include "db_config.h"

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

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

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

        /*
         * 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.
         */
        switch (TYPE(h)) {
        case P_LBTREE:
        case P_LDUP:
        case P_LRECNO:
                bk = GET_BKEYDATA(dbp, h, indx);
                if (B_TYPE(bk->type) == B_OVERFLOW)
                        bo = (BOVERFLOW *)bk;
                else {
                        pg_dbt.data = bk->data;
                        pg_dbt.size = bk->len;
                        *cmpp = func(dbp, dbt, &pg_dbt);
                        return (0);
                }
                break;
        case P_IBTREE:
                /*
                 * The following code guarantees that the left-most key on an
                 * internal page at any place in the tree sorts less than any
                 * user-specified key.  The reason is that if we have reached
                 * this internal page, we know the user key must sort greater
                 * than the key we're storing for this page in any internal
                 * pages at levels above us in the tree.  It then follows that
                 * any user-specified key cannot sort less than the first page
                 * which we reference, and so there's no reason to call the
                 * comparison routine.  While this may save us a comparison
                 * routine call or two, the real reason for this is because
                 * we don't maintain a copy of the smallest key in the tree,
                 * so that we don't have to update all the levels of the tree
                 * should the application store a new smallest key.  And, so,
                 * we may not have a key to compare, which makes doing the
                 * comparison difficult and error prone.
                 */
                if (indx == 0) {
                        *cmpp = 1;
                        return (0);
                }

                bi = GET_BINTERNAL(dbp, h, indx);
                if (B_TYPE(bi->type) == B_OVERFLOW)
                        bo = (BOVERFLOW *)(bi->data);
                else {
                        pg_dbt.data = bi->data;
                        pg_dbt.size = bi->len;
                        *cmpp = func(dbp, dbt, &pg_dbt);
                        return (0);
                }
                break;
        default:
                return (__db_pgfmt(dbp->dbenv, PGNO(h)));
        }

        /*
         * Overflow.
         */
        return (__db_moff(dbp, dbt,
            bo->pgno, bo->tlen, func == __bam_defcmp ? NULL : func, cmpp));
}

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

        COMPQUIET(dbp, NULL);

        /*
         * 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((DB *, const DBT *, const DBT *));
 */
size_t
__bam_defpfx(dbp, a, b)
        DB *dbp;
        const DBT *a, *b;
{
        size_t cnt, len;
        u_int8_t *p1, *p2;

        COMPQUIET(dbp, NULL);

        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);

        /*
         * They match up to the smaller of the two sizes.
         * Collate the longer after the shorter.
         */
        if (a->size < b->size)
                return (a->size + 1);
        if (b->size < a->size)
                return (b->size + 1);
        return (b->size);
}

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