lib/libc/db/btree/lruhash.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.
 *
 * 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[] = "@(#)lruhash.c   5.2 (Berkeley) 2/22/91";
#endif /* LIBC_SCCS and not lint */

#include <stdlib.h>
#include "lrucache.h"

#define HASH(l, pgno)   (pgno % l->lru_csize)

/*
 *  LRUHASHGET -- Look up a block in the LRU cache by page number.
 *
 *      Parameters:
 *              l -- LRU cache
 *              pgno -- number of the logical page to get
 *
 *      Returns:
 *              (CACHE_ENT *) pointer to the associated hash table entry
 *              (if any), or NULL (if none).
 */

CACHE_ENT *
lruhashget(l, pgno)
        LRUCACHE *l;
        int pgno;
{
        int hashind;
        CACHE_ENT *ce;

        hashind = HASH(l, pgno);

        /* walk the chain */
        for (ce = l->lru_cache[hashind];
             ce != (CACHE_ENT *) NULL;
             ce = ce->c_chain) {
                if (ce->c_pgno == pgno)
                        return (ce);
        }

        return ((CACHE_ENT *) NULL);
}

/*
 *  LRUHASHPUT -- Add an entry for a given page to the cache hash table.
 *
 *      This routine assumes that the given page does not yet have an entry
 *      in the table.
 *
 *      Parameters:
 *              l -- LRU cache
 *              pgno -- logical page number for this entry
 *              lruent -- LRU list entry at which hash table entry should
 *                        point
 *
 *      Returns:
 *              (CACHE_ENT *) pointer to the new hash table entry on success,
 *              or NULL on failure.
 *
 *      Side Effects:
 *              Allocates memory which should be freed when the hash table
 *              entry is removed.
 */

CACHE_ENT *
lruhashput(l, pgno, lruent)
        LRUCACHE *l;
        int pgno;
        LRU_ENT *lruent;
{
        int hashind;
        CACHE_ENT *ce;

        if ((ce = (CACHE_ENT *) malloc((unsigned) sizeof(CACHE_ENT)))
            == (CACHE_ENT *) NULL)
                return ((CACHE_ENT *) NULL);

        hashind = HASH(l, pgno);

        ce->c_pgno = pgno;
        ce->c_lruent = lruent;
        ce->c_chain = l->lru_cache[hashind];
        l->lru_cache[hashind] = ce;

        return (ce);
}

/*
 *  LRUHASHDEL -- Delete the entry for a given page from the LRU cache
 *                hash table.
 *
 *      Parameters:
 *              l -- LRU cache
 *              pgno -- page number for which we should delete htable entry
 *
 *      Returns:
 *              Zero on success, -1 on failure.
 *
 *      Side Effects:
 *              Releases the memory occupied by the hash table entry.
 */

int
lruhashdel(l, pgno)
        LRUCACHE *l;
        int pgno;
{
        CACHE_ENT *ce;
        CACHE_ENT *sce;
        int hashind;

        sce = (CACHE_ENT *) NULL;
        hashind = HASH(l, pgno);

        /* find the entry we want to delete */
        for (ce = l->lru_cache[hashind];
             ce != (CACHE_ENT *) NULL;
             ce = ce->c_chain) {
                if (ce->c_pgno == pgno)
                        break;
                sce = ce;
        }

        if (ce == (CACHE_ENT *) NULL)
                return (-1);

        /* remove it from the chain */
        if (sce == (CACHE_ENT *) NULL)
                l->lru_cache[hashind] = ce->c_chain;
        else
                sce->c_chain = ce->c_chain;

        /* release it */
        free ((char *) ce);

        /* success */
        return (0);
}