/* xf86drmHash.c -- Small hash table support for integer -> integer mapping
* Created: Sun Apr 18 09:35:45 1999 by faith@precisioninsight.com
*
* Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
* All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*
* Authors: Rickard E. (Rik) Faith <faith@valinux.com>
*
* DESCRIPTION
*
* This file contains a straightforward implementation of a fixed-sized
* hash table using self-organizing linked lists [Knuth73, pp. 398-399] for
* collision resolution. There are two potentially interesting things
* about this implementation:
*
* 1) The table is power-of-two sized. Prime sized tables are more
* traditional, but do not have a significant advantage over power-of-two
* sized table, especially when double hashing is not used for collision
* resolution.
*
* 2) The hash computation uses a table of random integers [Hanson97,
* pp. 39-41].
*
* FUTURE ENHANCEMENTS
*
* With a table size of 512, the current implementation is sufficient for a
* few hundred keys. Since this is well above the expected size of the
* tables for which this implementation was designed, the implementation of
* dynamic hash tables was postponed until the need arises. A common (and
* naive) approach to dynamic hash table implementation simply creates a
* new hash table when necessary, rehashes all the data into the new table,
* and destroys the old table. The approach in [Larson88] is superior in
* two ways: 1) only a portion of the table is expanded when needed,
* distributing the expansion cost over several insertions, and 2) portions
* of the table can be locked, enabling a scalable thread-safe
* implementation.
*
* REFERENCES
*
* [Hanson97] David R. Hanson. C Interfaces and Implementations:
* Techniques for Creating Reusable Software. Reading, Massachusetts:
* Addison-Wesley, 1997.
*
* [Knuth73] Donald E. Knuth. The Art of Computer Programming. Volume 3:
* Sorting and Searching. Reading, Massachusetts: Addison-Wesley, 1973.
*
* [Larson88] Per-Ake Larson. "Dynamic Hash Tables". CACM 31(4), April
* 1988, pp. 446-457.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include "xf86drm.h"
#include "xf86drmHash.h"
#define HASH_MAGIC 0xdeadbeef
static unsigned long HashHash(unsigned long key)
{
unsigned long hash = 0;
unsigned long tmp = key;
static int init = 0;
static unsigned long scatter[256];
int i;
if (!init) {
void *state;
state = drmRandomCreate(37);
for (i = 0; i < 256; i++) scatter[i] = drmRandom(state);
drmRandomDestroy(state);
++init;
}
while (tmp) {
hash = (hash << 1) + scatter[tmp & 0xff];
tmp >>= 8;
}
hash %= HASH_SIZE;
#if DEBUG
printf( "Hash(%lu) = %lu\n", key, hash);
#endif
return hash;
}
void *drmHashCreate(void)
{
HashTablePtr table;
int i;
table = drmMalloc(sizeof(*table));
if (!table) return NULL;
table->magic = HASH_MAGIC;
table->entries = 0;
table->hits = 0;
table->partials = 0;
table->misses = 0;
for (i = 0; i < HASH_SIZE; i++) table->buckets[i] = NULL;
return table;
}
int drmHashDestroy(void *t)
{
HashTablePtr table = (HashTablePtr)t;
HashBucketPtr bucket;
HashBucketPtr next;
int i;
if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
for (i = 0; i < HASH_SIZE; i++) {
for (bucket = table->buckets[i]; bucket;) {
next = bucket->next;
drmFree(bucket);
bucket = next;
}
}
drmFree(table);
return 0;
}
/* Find the bucket and organize the list so that this bucket is at the
top. */
static HashBucketPtr HashFind(HashTablePtr table,
unsigned long key, unsigned long *h)
{
unsigned long hash = HashHash(key);
HashBucketPtr prev = NULL;
HashBucketPtr bucket;
if (h) *h = hash;
for (bucket = table->buckets[hash]; bucket; bucket = bucket->next) {
if (bucket->key == key) {
if (prev) {
/* Organize */
prev->next = bucket->next;
bucket->next = table->buckets[hash];
table->buckets[hash] = bucket;
++table->partials;
} else {
++table->hits;
}
return bucket;
}
prev = bucket;
}
++table->misses;
return NULL;
}
int drmHashLookup(void *t, unsigned long key, void **value)
{
HashTablePtr table = (HashTablePtr)t;
HashBucketPtr bucket;
if (!table || table->magic != HASH_MAGIC) return -1; /* Bad magic */
bucket = HashFind(table, key, NULL);
if (!bucket) return 1; /* Not found */
*value = bucket->value;
return 0; /* Found */
}
int drmHashInsert(void *t, unsigned long key, void *value)
{
HashTablePtr table = (HashTablePtr)t;
HashBucketPtr bucket;
unsigned long hash;
if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
if (HashFind(table, key, &hash)) return 1; /* Already in table */
bucket = drmMalloc(sizeof(*bucket));
if (!bucket) return -1; /* Error */
bucket->key = key;
bucket->value = value;
bucket->next = table->buckets[hash];
table->buckets[hash] = bucket;
#if DEBUG
printf("Inserted %lu at %lu/%p\n", key, hash, bucket);
#endif
return 0; /* Added to table */
}
int drmHashDelete(void *t, unsigned long key)
{
HashTablePtr table = (HashTablePtr)t;
unsigned long hash;
HashBucketPtr bucket;
if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
bucket = HashFind(table, key, &hash);
if (!bucket) return 1; /* Not found */
table->buckets[hash] = bucket->next;
drmFree(bucket);
return 0;
}
int drmHashNext(void *t, unsigned long *key, void **value)
{
HashTablePtr table = (HashTablePtr)t;
while (table->p0 < HASH_SIZE) {
if (table->p1) {
*key = table->p1->key;
*value = table->p1->value;
table->p1 = table->p1->next;
return 1;
}
table->p1 = table->buckets[table->p0];
++table->p0;
}
return 0;
}
int drmHashFirst(void *t, unsigned long *key, void **value)
{
HashTablePtr table = (HashTablePtr)t;
if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
table->p0 = 0;
table->p1 = table->buckets[0];
return drmHashNext(table, key, value);
}