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lruhash.c
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1993-05-22
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#include <stdlib.h>
#include "cdefs.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 *) cbMALLOC((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);
}