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
HashHash(unsigned long key)80 static 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
drmHashCreate(void)105 drm_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
drmHashDestroy(void * t)116 drm_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
HashFind(HashTablePtr table,unsigned long key,unsigned long * h)139 static 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
drmHashLookup(void * t,unsigned long key,void ** value)167 drm_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
drmHashInsert(void * t,unsigned long key,void * value)180 drm_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
drmHashDelete(void * t,unsigned long key)199 drm_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
drmHashNext(void * t,unsigned long * key,void ** value)216 drm_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
drmHashFirst(void * t,unsigned long * key,void ** value)233 drm_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