1 /* xf86drmHash.c -- Small hash table support for integer -> integer mapping
2 * Created: Sun Apr 18 09:35:45 1999 by [email protected]
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 <[email protected]>
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 #include <errno.h>
74
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 if (!state)
92 return HASH_INVALID;
93 for (i = 0; i < 256; i++) scatter[i] = drmRandom(state);
94 drmRandomDestroy(state);
95 ++init;
96 }
97
98 while (tmp) {
99 hash = (hash << 1) + scatter[tmp & 0xff];
100 tmp >>= 8;
101 }
102
103 hash %= HASH_SIZE;
104 #if DEBUG
105 printf( "Hash(%lu) = %lu\n", key, hash);
106 #endif
107 return hash;
108 }
109
drmHashCreate(void)110 void *drmHashCreate(void)
111 {
112 HashTablePtr table;
113 int i;
114
115 table = (HashTablePtr)drmMalloc(sizeof(*table));
116 if (!table) return nullptr;
117 table->magic = HASH_MAGIC;
118 table->entries = 0;
119 table->hits = 0;
120 table->partials = 0;
121 table->misses = 0;
122
123 for (i = 0; i < HASH_SIZE; i++) table->buckets[i] = nullptr;
124 return table;
125 }
126
drmHashDestroy(void * t)127 int drmHashDestroy(void *t)
128 {
129 HashTablePtr table = (HashTablePtr)t;
130 HashBucketPtr bucket;
131 HashBucketPtr next;
132 int i;
133
134 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
135
136 for (i = 0; i < HASH_SIZE; i++) {
137 for (bucket = table->buckets[i]; bucket;) {
138 next = bucket->next;
139 drmFree(bucket);
140 bucket = next;
141 }
142 }
143 drmFree(table);
144 return 0;
145 }
146
147 /* Find the bucket and organize the list so that this bucket is at the
148 top. */
149
HashFind(HashTablePtr table,unsigned long key,unsigned long * h)150 static HashBucketPtr HashFind(HashTablePtr table,
151 unsigned long key, unsigned long *h)
152 {
153 unsigned long hash = HashHash(key);
154 HashBucketPtr prev = nullptr;
155 HashBucketPtr bucket;
156
157 if (h) *h = hash;
158
159 if (hash == HASH_INVALID)
160 return nullptr;
161
162 for (bucket = table->buckets[hash]; bucket; bucket = bucket->next) {
163 if (bucket->key == key) {
164 if (prev) {
165 /* Organize */
166 prev->next = bucket->next;
167 bucket->next = table->buckets[hash];
168 table->buckets[hash] = bucket;
169 ++table->partials;
170 } else {
171 ++table->hits;
172 }
173 return bucket;
174 }
175 prev = bucket;
176 }
177 ++table->misses;
178 return nullptr;
179 }
180
drmHashLookup(void * t,unsigned long key,void ** value)181 int drmHashLookup(void *t, unsigned long key, void **value)
182 {
183 HashTablePtr table = (HashTablePtr)t;
184 HashBucketPtr bucket;
185
186 if (!table || table->magic != HASH_MAGIC) return -1; /* Bad magic */
187
188 bucket = HashFind(table, key, nullptr);
189 if (!bucket) return 1; /* Not found */
190 *value = bucket->value;
191 return 0; /* Found */
192 }
193
drmHashInsert(void * t,unsigned long key,void * value)194 int drmHashInsert(void *t, unsigned long key, void *value)
195 {
196 HashTablePtr table = (HashTablePtr)t;
197 HashBucketPtr bucket;
198 unsigned long hash;
199
200 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
201
202 if (HashFind(table, key, &hash)) return 1; /* Already in table */
203 if (hash == HASH_INVALID) return -1;
204
205 bucket = (HashBucketPtr)drmMalloc(sizeof(*bucket));
206 if (!bucket) return -1; /* Error */
207 bucket->key = key;
208 bucket->value = value;
209 bucket->next = table->buckets[hash];
210 table->buckets[hash] = bucket;
211 #if DEBUG
212 printf("Inserted %lu at %lu/%p\n", key, hash, bucket);
213 #endif
214 return 0; /* Added to table */
215 }
216
drmHashDelete(void * t,unsigned long key)217 int drmHashDelete(void *t, unsigned long key)
218 {
219 HashTablePtr table = (HashTablePtr)t;
220 unsigned long hash;
221 HashBucketPtr bucket;
222
223 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
224
225 bucket = HashFind(table, key, &hash);
226
227 if (hash == HASH_INVALID) return -1;
228 if (!bucket) return 1; /* Not found */
229
230 table->buckets[hash] = bucket->next;
231 drmFree(bucket);
232 return 0;
233 }
234