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