245 lines
6.6 KiB
C
245 lines
6.6 KiB
C
/*-
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* Copyright (c) 1990 The Regents of the University of California.
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* All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Mike Olson.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#if defined(LIBC_SCCS) && !defined(lint)
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static char sccsid[] = "@(#)lrutils.c 5.2 (Berkeley) 2/22/91";
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#endif /* LIBC_SCCS and not lint */
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#include <stdlib.h>
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#include <string.h>
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#include "lrucache.h"
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/*
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* LRUGETPG -- Get a free page from the LRU cache.
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*
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* This routine grows the cache if necessary, finds an unused page if
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* it can, and handles flushing dirty buffers to disk.
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*
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* One of the parameters to this routine (f) is the routine that called
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* us. If we have to grow the cache, we call this routine recursively
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* in order to fill the buffer. The reason for this is that we have
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* two interfaces that call lrugetpg(). Lruget() fills a page from disk,
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* and lrugetnew() just allocates a new (empty) page.
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*
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* Parameters:
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* l -- LRU cache to use.
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* pgno -- page number for which we want a buffer
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* nread -- pointer to an int to get number of bytes read
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* f -- who called us
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*
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* Returns:
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* (char *) pointer to buffer to use, or NULL on failure.
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*
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* Warnings:
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* The buffer returned is locked down until the user does an
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* explicit lrurelease() on it.
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*/
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char *
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lrugetpg(l, pgno, nread, f)
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LRUCACHE *l;
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int pgno;
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int *nread;
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char *(*f)();
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{
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CACHE_ENT *ce;
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LRU_ENT *lruent;
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char *buffer;
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/* if we're allowed to grow the cache, do so */
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if (l->lru_cursz < l->lru_csize) {
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/* get a buffer */
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if ((buffer = (char *) malloc((unsigned) l->lru_psize))
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== (char *) NULL)
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return ((char *) NULL);
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/* get and LRU list entry */
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if ((lruent = (LRU_ENT *) malloc((unsigned) sizeof(LRU_ENT)))
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== (LRU_ENT *) NULL)
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return ((char *) NULL);
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lruent->l_buffer = buffer;
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lruent->l_pgno = pgno;
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lruent->l_flags = NULL;
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/* manage spaghetti */
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lruent->l_prev = (LRU_ENT *) NULL;
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lruent->l_next = l->lru_head;
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if (l->lru_head != (LRU_ENT *) NULL)
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l->lru_head->l_prev = lruent;
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l->lru_head = lruent;
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if (l->lru_tail == (LRU_ENT *) NULL)
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l->lru_tail = lruent;
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/* add it to the hash table */
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ce = lruhashput(l, pgno, lruent);
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l->lru_cursz++;
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} else {
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lruent = l->lru_tail;
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/* find the oldest unused buffer */
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while (lruent != (LRU_ENT *) NULL
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&& !(lruent->l_flags & F_FREE))
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lruent = lruent->l_prev;
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/* if no free buffer was found, we have to grow the cache */
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if (lruent == (LRU_ENT *) NULL) {
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if (lrugrow(l) < 0)
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return ((char *) NULL);
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return ((*f)((LRU) l, pgno, nread));
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}
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/* okay, found a free buffer -- update hash table and list */
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ce = lruhashget(l, lruent->l_pgno);
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if (lruhashdel(l, lruent->l_pgno) < 0)
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return ((char *) NULL);
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/* flush the old page to disk, if necessary */
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if (lruent->l_flags & F_DIRTY)
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if (lruflush(l, lruent) < 0)
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return ((char *) NULL);
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/* update stats, hash table, and list */
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lruent->l_pgno = pgno;
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lruhead(l, lruent);
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ce = lruhashput(l, pgno, lruent);
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buffer = lruent->l_buffer;
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}
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#ifdef lint
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ce = ce;
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#endif /* lint */
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/* lock this page down */
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lruent->l_flags &= ~F_FREE;
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return (buffer);
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}
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/*
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* LRUHEAD -- Move an LRU list entry to the head of the list.
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*
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* The head of the list is where the most recently used item goes.
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*
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* Parameters:
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* l -- LRU cache
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* lruent -- entry to move to the head of the list
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*
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* Returns:
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* None
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*
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* Side Effects:
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* Updates the cache's head and tail pointers as required.
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*/
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void
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lruhead(l, lruent)
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LRUCACHE *l;
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LRU_ENT *lruent;
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{
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LRU_ENT *next;
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LRU_ENT *prev;
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if (l->lru_head == lruent)
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return;
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next = lruent->l_next;
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prev = lruent->l_prev;
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lruent->l_prev = (LRU_ENT *) NULL;
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lruent->l_next = l->lru_head;
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l->lru_head->l_prev = lruent;
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l->lru_head = lruent;
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prev->l_next = next;
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if (next != (LRU_ENT *) NULL)
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next->l_prev = prev;
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if (l->lru_tail == lruent)
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l->lru_tail = prev;
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}
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/*
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* LRUGROW -- Grow the LRU cache
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*
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* This routine is called only if we can't satisfy a user's get() request
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* using an existing buffer. We need to rebuild the hash table so that
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* subsequent lookups work correctly, since the cache size is used to
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* compute hash keys.
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*
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* Parameters:
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* l -- LRU cache to grow
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*
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* Returns:
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* Zero on success, -1 on failure
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*/
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int
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lrugrow(l)
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LRUCACHE *l;
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{
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int oldsz, newsz;
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CACHE_ENT **new;
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CACHE_ENT *ce, *nce;
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int h;
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int i;
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oldsz = l->lru_csize;
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newsz = l->lru_csize + 1;
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/* get a new hash table */
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if ((new = (CACHE_ENT **) malloc((unsigned)newsz * sizeof(CACHE_ENT *)))
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== (CACHE_ENT **) NULL)
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return (-1);
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/* build the new hash table */
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bzero((char *) new, (size_t) (newsz * sizeof(CACHE_ENT *)));
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for (i = oldsz; --i >= 0; ) {
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for (ce = l->lru_cache[i]; ce != (CACHE_ENT *) NULL; ) {
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nce = ce->c_chain;
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h = ce->c_pgno % newsz;
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ce->c_chain = new[h];
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new[h] = ce;
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ce = nce;
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}
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}
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/* get rid of the old hash table, and update the cache */
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free ((char *) (l->lru_cache));
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l->lru_cache = new;
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l->lru_csize = newsz;
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return (0);
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}
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