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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996, 1997
* Sleepycat Software. All rights reserved.
*/
#include "config.h"
#ifndef lint
static const char sccsid[] = "@(#)db_shash.c 10.3 (Sleepycat) 6/21/97";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#endif
#include "db_int.h"
#include "shqueue.h"
#include "common_ext.h"
/* Powers-of-2 and close-by prime number pairs. */
static const struct {
int power;
int prime;
} list[] = {
{ 64, 67},
{ 128, 131},
{ 256, 257},
{ 512, 521},
{1024, 1031},
{2048, 2053},
{4096, 4099},
{8192, 8191},
{0, 0}
};
/*
* __db_tablesize --
* Choose a size for the hash table.
*
* PUBLIC: int __db_tablesize __P((int));
*/
int
__db_tablesize(n_buckets)
int n_buckets;
{
int i;
/*
* We try to be clever about how big we make the hash tables. Pick
* a prime number close to the "suggested" number of elements that
* will be in the hash table. We shoot for minimum collisions (i.e.
* one element in each bucket). We use 64 as the minimum table size.
*
* Ref: Sedgewick, Algorithms in C, "Hash Functions"
*/
if (n_buckets < 64)
n_buckets = 64;
for (i = 0;; ++i) {
if (list[i].power == 0) {
--i;
break;
}
if (list[i].power >= n_buckets)
break;
}
return (list[i].prime);
}
/*
* __db_hashinit --
* Initialize a hash table that resides in shared memory.
*
* PUBLIC: void __db_hashinit __P((void *, int));
*/
void
__db_hashinit(begin, nelements)
void *begin;
int nelements;
{
int i;
SH_TAILQ_HEAD(hash_head) *headp;
headp = (struct hash_head *)begin;
for (i = 0; i < nelements; i++, headp++)
SH_TAILQ_INIT(headp);
}
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