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 "xf86drm.h"
75 #include "xf86drmHash.h"
76
77 #define HASH_MAGIC 0xdeadbeef
78
HashHash(unsigned long key)79 static unsigned long HashHash(unsigned long key)
80 {
81 unsigned long hash = 0;
82 unsigned long tmp = key;
83 static int init = 0;
84 static unsigned long scatter[256];
85 int i;
86
87 if (!init) {
88 void *state;
89 state = drmRandomCreate(37);
90 for (i = 0; i < 256; i++) scatter[i] = drmRandom(state);
91 drmRandomDestroy(state);
92 ++init;
93 }
94
95 while (tmp) {
96 hash = (hash << 1) + scatter[tmp & 0xff];
97 tmp >>= 8;
98 }
99
100 hash %= HASH_SIZE;
101 #if DEBUG
102 printf( "Hash(%lu) = %lu\n", key, hash);
103 #endif
104 return hash;
105 }
106
drmHashCreate(void)107 void *drmHashCreate(void)
108 {
109 HashTablePtr table;
110 int i;
111
112 table = drmMalloc(sizeof(*table));
113 if (!table) return NULL;
114 table->magic = HASH_MAGIC;
115 table->entries = 0;
116 table->hits = 0;
117 table->partials = 0;
118 table->misses = 0;
119
120 for (i = 0; i < HASH_SIZE; i++) table->buckets[i] = NULL;
121 return table;
122 }
123
drmHashDestroy(void * t)124 int drmHashDestroy(void *t)
125 {
126 HashTablePtr table = (HashTablePtr)t;
127 HashBucketPtr bucket;
128 HashBucketPtr next;
129 int i;
130
131 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
132
133 for (i = 0; i < HASH_SIZE; i++) {
134 for (bucket = table->buckets[i]; bucket;) {
135 next = bucket->next;
136 drmFree(bucket);
137 bucket = next;
138 }
139 }
140 drmFree(table);
141 return 0;
142 }
143
144 /* Find the bucket and organize the list so that this bucket is at the
145 top. */
146
HashFind(HashTablePtr table,unsigned long key,unsigned long * h)147 static HashBucketPtr HashFind(HashTablePtr table,
148 unsigned long key, unsigned long *h)
149 {
150 unsigned long hash = HashHash(key);
151 HashBucketPtr prev = NULL;
152 HashBucketPtr bucket;
153
154 if (h) *h = hash;
155
156 for (bucket = table->buckets[hash]; bucket; bucket = bucket->next) {
157 if (bucket->key == key) {
158 if (prev) {
159 /* Organize */
160 prev->next = bucket->next;
161 bucket->next = table->buckets[hash];
162 table->buckets[hash] = bucket;
163 ++table->partials;
164 } else {
165 ++table->hits;
166 }
167 return bucket;
168 }
169 prev = bucket;
170 }
171 ++table->misses;
172 return NULL;
173 }
174
drmHashLookup(void * t,unsigned long key,void ** value)175 int drmHashLookup(void *t, unsigned long key, void **value)
176 {
177 HashTablePtr table = (HashTablePtr)t;
178 HashBucketPtr bucket;
179
180 if (!table || table->magic != HASH_MAGIC) return -1; /* Bad magic */
181
182 bucket = HashFind(table, key, NULL);
183 if (!bucket) return 1; /* Not found */
184 *value = bucket->value;
185 return 0; /* Found */
186 }
187
drmHashInsert(void * t,unsigned long key,void * value)188 int drmHashInsert(void *t, unsigned long key, void *value)
189 {
190 HashTablePtr table = (HashTablePtr)t;
191 HashBucketPtr bucket;
192 unsigned long hash;
193
194 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
195
196 if (HashFind(table, key, &hash)) return 1; /* Already in table */
197
198 bucket = drmMalloc(sizeof(*bucket));
199 if (!bucket) return -1; /* Error */
200 bucket->key = key;
201 bucket->value = value;
202 bucket->next = table->buckets[hash];
203 table->buckets[hash] = bucket;
204 #if DEBUG
205 printf("Inserted %lu at %lu/%p\n", key, hash, bucket);
206 #endif
207 return 0; /* Added to table */
208 }
209
drmHashDelete(void * t,unsigned long key)210 int drmHashDelete(void *t, unsigned long key)
211 {
212 HashTablePtr table = (HashTablePtr)t;
213 unsigned long hash;
214 HashBucketPtr bucket;
215
216 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
217
218 bucket = HashFind(table, key, &hash);
219
220 if (!bucket) return 1; /* Not found */
221
222 table->buckets[hash] = bucket->next;
223 drmFree(bucket);
224 return 0;
225 }
226
drmHashNext(void * t,unsigned long * key,void ** value)227 int drmHashNext(void *t, unsigned long *key, void **value)
228 {
229 HashTablePtr table = (HashTablePtr)t;
230
231 while (table->p0 < HASH_SIZE) {
232 if (table->p1) {
233 *key = table->p1->key;
234 *value = table->p1->value;
235 table->p1 = table->p1->next;
236 return 1;
237 }
238 table->p1 = table->buckets[table->p0];
239 ++table->p0;
240 }
241 return 0;
242 }
243
drmHashFirst(void * t,unsigned long * key,void ** value)244 int drmHashFirst(void *t, unsigned long *key, void **value)
245 {
246 HashTablePtr table = (HashTablePtr)t;
247
248 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
249
250 table->p0 = 0;
251 table->p1 = table->buckets[0];
252 return drmHashNext(table, key, value);
253 }
254