1/* xf86drmHash.c -- Small hash table support for integer -> integer mapping
2 * Created: Sun Apr 18 09:35:45 1999 by faith@precisioninsight.com
3 *
4 * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
5 * All Rights Reserved.
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a
8 * copy of this software and associated documentation files (the "Software"),
9 * to deal in the Software without restriction, including without limitation
10 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
11 * and/or sell copies of the Software, and to permit persons to whom the
12 * Software is furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice (including the next
15 * paragraph) shall be included in all copies or substantial portions of the
16 * Software.
17 *
18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
21 * PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
22 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
23 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
24 * DEALINGS IN THE SOFTWARE.
25 *
26 * Authors: Rickard E. (Rik) Faith <faith@valinux.com>
27 *
28 * DESCRIPTION
29 *
30 * This file contains a straightforward implementation of a fixed-sized
31 * hash table using self-organizing linked lists [Knuth73, pp. 398-399] for
32 * collision resolution.  There are two potentially interesting things
33 * about this implementation:
34 *
35 * 1) The table is power-of-two sized.  Prime sized tables are more
36 * traditional, but do not have a significant advantage over power-of-two
37 * sized table, especially when double hashing is not used for collision
38 * resolution.
39 *
40 * 2) The hash computation uses a table of random integers [Hanson97,
41 * pp. 39-41].
42 *
43 * FUTURE ENHANCEMENTS
44 *
45 * With a table size of 512, the current implementation is sufficient for a
46 * few hundred keys.  Since this is well above the expected size of the
47 * tables for which this implementation was designed, the implementation of
48 * dynamic hash tables was postponed until the need arises.  A common (and
49 * naive) approach to dynamic hash table implementation simply creates a
50 * new hash table when necessary, rehashes all the data into the new table,
51 * and destroys the old table.  The approach in [Larson88] is superior in
52 * two ways: 1) only a portion of the table is expanded when needed,
53 * distributing the expansion cost over several insertions, and 2) portions
54 * of the table can be locked, enabling a scalable thread-safe
55 * implementation.
56 *
57 * REFERENCES
58 *
59 * [Hanson97] David R. Hanson.  C Interfaces and Implementations:
60 * Techniques for Creating Reusable Software.  Reading, Massachusetts:
61 * Addison-Wesley, 1997.
62 *
63 * [Knuth73] Donald E. Knuth. The Art of Computer Programming.  Volume 3:
64 * Sorting and Searching.  Reading, Massachusetts: Addison-Wesley, 1973.
65 *
66 * [Larson88] Per-Ake Larson. "Dynamic Hash Tables".  CACM 31(4), April
67 * 1988, pp. 446-457.
68 *
69 */
70
71#include <stdio.h>
72#include <stdlib.h>
73
74#include "libdrm_macros.h"
75#include "xf86drm.h"
76#include "xf86drmHash.h"
77
78#define HASH_MAGIC 0xdeadbeef
79
80static unsigned long HashHash(unsigned long key)
81{
82    unsigned long        hash = 0;
83    unsigned long        tmp  = key;
84    static int           init = 0;
85    static unsigned long scatter[256];
86    int                  i;
87
88    if (!init) {
89	void *state;
90	state = drmRandomCreate(37);
91	for (i = 0; i < 256; i++) scatter[i] = drmRandom(state);
92	drmRandomDestroy(state);
93	++init;
94    }
95
96    while (tmp) {
97	hash = (hash << 1) + scatter[tmp & 0xff];
98	tmp >>= 8;
99    }
100
101    hash %= HASH_SIZE;
102    return hash;
103}
104
105drm_public void *drmHashCreate(void)
106{
107    HashTablePtr table;
108
109    table           = drmMalloc(sizeof(*table));
110    if (!table) return NULL;
111    table->magic    = HASH_MAGIC;
112
113    return table;
114}
115
116drm_public int drmHashDestroy(void *t)
117{
118    HashTablePtr  table = (HashTablePtr)t;
119    HashBucketPtr bucket;
120    HashBucketPtr next;
121    int           i;
122
123    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
124
125    for (i = 0; i < HASH_SIZE; i++) {
126	for (bucket = table->buckets[i]; bucket;) {
127	    next = bucket->next;
128	    drmFree(bucket);
129	    bucket = next;
130	}
131    }
132    drmFree(table);
133    return 0;
134}
135
136/* Find the bucket and organize the list so that this bucket is at the
137   top. */
138
139static HashBucketPtr HashFind(HashTablePtr table,
140			      unsigned long key, unsigned long *h)
141{
142    unsigned long hash = HashHash(key);
143    HashBucketPtr prev = NULL;
144    HashBucketPtr bucket;
145
146    if (h) *h = hash;
147
148    for (bucket = table->buckets[hash]; bucket; bucket = bucket->next) {
149	if (bucket->key == key) {
150	    if (prev) {
151				/* Organize */
152		prev->next           = bucket->next;
153		bucket->next         = table->buckets[hash];
154		table->buckets[hash] = bucket;
155		++table->partials;
156	    } else {
157		++table->hits;
158	    }
159	    return bucket;
160	}
161	prev = bucket;
162    }
163    ++table->misses;
164    return NULL;
165}
166
167drm_public int drmHashLookup(void *t, unsigned long key, void **value)
168{
169    HashTablePtr  table = (HashTablePtr)t;
170    HashBucketPtr bucket;
171
172    if (!table || table->magic != HASH_MAGIC) return -1; /* Bad magic */
173
174    bucket = HashFind(table, key, NULL);
175    if (!bucket) return 1;	/* Not found */
176    *value = bucket->value;
177    return 0;			/* Found */
178}
179
180drm_public int drmHashInsert(void *t, unsigned long key, void *value)
181{
182    HashTablePtr  table = (HashTablePtr)t;
183    HashBucketPtr bucket;
184    unsigned long hash;
185
186    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
187
188    if (HashFind(table, key, &hash)) return 1; /* Already in table */
189
190    bucket               = drmMalloc(sizeof(*bucket));
191    if (!bucket) return -1;	/* Error */
192    bucket->key          = key;
193    bucket->value        = value;
194    bucket->next         = table->buckets[hash];
195    table->buckets[hash] = bucket;
196    return 0;			/* Added to table */
197}
198
199drm_public int drmHashDelete(void *t, unsigned long key)
200{
201    HashTablePtr  table = (HashTablePtr)t;
202    unsigned long hash;
203    HashBucketPtr bucket;
204
205    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
206
207    bucket = HashFind(table, key, &hash);
208
209    if (!bucket) return 1;	/* Not found */
210
211    table->buckets[hash] = bucket->next;
212    drmFree(bucket);
213    return 0;
214}
215
216drm_public int drmHashNext(void *t, unsigned long *key, void **value)
217{
218    HashTablePtr  table = (HashTablePtr)t;
219
220    while (table->p0 < HASH_SIZE) {
221	if (table->p1) {
222	    *key       = table->p1->key;
223	    *value     = table->p1->value;
224	    table->p1  = table->p1->next;
225	    return 1;
226	}
227	table->p1 = table->buckets[table->p0];
228	++table->p0;
229    }
230    return 0;
231}
232
233drm_public int drmHashFirst(void *t, unsigned long *key, void **value)
234{
235    HashTablePtr  table = (HashTablePtr)t;
236
237    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
238
239    table->p0 = 0;
240    table->p1 = table->buckets[0];
241    return drmHashNext(table, key, value);
242}
243