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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996, 1997, 1998, 1999, 2000
* Sleepycat Software. All rights reserved.
*/
#include "db_config.h"
#ifndef lint
static const char revid[] = "$Id: db_shash.c,v 11.3 2000/02/14 02:59:49 bostic Exp $";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#endif
#include "db_int.h"
/*
* Table of good hash values. Up to ~250,000 buckets, we use powers of 2.
* After that, we slow the rate of increase by half. For each choice, we
* then use a nearby prime number as the hash value.
*
* If a terabyte is the maximum cache we'll see, and we assume there are
* 10 1K buckets on each hash chain, then 107374182 is the maximum number
* of buckets we'll ever need.
*/
static const struct {
u_int32_t power;
u_int32_t prime;
} list[] = {
{ 64, 67}, /* 2^6 */
{ 128, 131}, /* 2^7 */
{ 256, 257}, /* 2^8 */
{ 512, 521}, /* 2^9 */
{ 1024, 1031}, /* 2^10 */
{ 2048, 2053}, /* 2^11 */
{ 4096, 4099}, /* 2^12 */
{ 8192, 8191}, /* 2^13 */
{ 16384, 16381}, /* 2^14 */
{ 32768, 32771}, /* 2^15 */
{ 65536, 65537}, /* 2^16 */
{ 131072, 131071}, /* 2^17 */
{ 262144, 262147}, /* 2^18 */
{ 393216, 393209}, /* 2^18 + 2^18/2 */
{ 524288, 524287}, /* 2^19 */
{ 786432, 786431}, /* 2^19 + 2^19/2 */
{ 1048576, 1048573}, /* 2^20 */
{ 1572864, 1572869}, /* 2^20 + 2^20/2 */
{ 2097152, 2097169}, /* 2^21 */
{ 3145728, 3145721}, /* 2^21 + 2^21/2 */
{ 4194304, 4194301}, /* 2^22 */
{ 6291456, 6291449}, /* 2^22 + 2^22/2 */
{ 8388608, 8388617}, /* 2^23 */
{ 12582912, 12582917}, /* 2^23 + 2^23/2 */
{ 16777216, 16777213}, /* 2^24 */
{ 25165824, 25165813}, /* 2^24 + 2^24/2 */
{ 33554432, 33554393}, /* 2^25 */
{ 50331648, 50331653}, /* 2^25 + 2^25/2 */
{ 67108864, 67108859}, /* 2^26 */
{ 100663296, 100663291}, /* 2^26 + 2^26/2 */
{ 134217728, 134217757}, /* 2^27 */
{ 201326592, 201326611}, /* 2^27 + 2^27/2 */
{ 268435456, 268435459}, /* 2^28 */
{ 402653184, 402653189}, /* 2^28 + 2^28/2 */
{ 536870912, 536870909}, /* 2^29 */
{ 805306368, 805306357}, /* 2^29 + 2^29/2 */
{1073741824, 1073741827}, /* 2^30 */
{0, 0}
};
/*
* __db_tablesize --
* Choose a size for the hash table.
*
* PUBLIC: int __db_tablesize __P((u_int32_t));
*/
int
__db_tablesize(n_buckets)
u_int32_t n_buckets;
{
int i;
/*
* We try to be clever about how big we make the hash tables. Use a
* prime number close to the "suggested" number of elements that will
* be in the hash table. Use 64 as the minimum hash 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 *, u_int32_t));
*/
void
__db_hashinit(begin, nelements)
void *begin;
u_int32_t nelements;
{
u_int32_t 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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