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 DIST_LIMIT 10
78 static int dist[DIST_LIMIT];
79 
80 static void clear_dist(void) {
81     int i;
82 
83     for (i = 0; i < DIST_LIMIT; i++)
84         dist[i] = 0;
85 }
86 
87 static int count_entries(HashBucketPtr bucket)
88 {
89     int count = 0;
90 
91     for (; bucket; bucket = bucket->next)
92         ++count;
93     return count;
94 }
95 
96 static void update_dist(int count)
97 {
98     if (count >= DIST_LIMIT)
99         ++dist[DIST_LIMIT-1];
100     else
101         ++dist[count];
102 }
103 
104 static void compute_dist(HashTablePtr table)
105 {
106     int           i;
107     HashBucketPtr bucket;
108 
109     printf("Entries = %ld, hits = %ld, partials = %ld, misses = %ld\n",
110           table->entries, table->hits, table->partials, table->misses);
111     clear_dist();
112     for (i = 0; i < HASH_SIZE; i++) {
113         bucket = table->buckets[i];
114         update_dist(count_entries(bucket));
115     }
116     for (i = 0; i < DIST_LIMIT; i++) {
117         if (i != DIST_LIMIT-1)
118             printf("%5d %10d\n", i, dist[i]);
119         else
120             printf("other %10d\n", dist[i]);
121     }
122 }
123 
124 static int check_table(HashTablePtr table,
125                        unsigned long key, void * value)
126 {
127     void *retval;
128     int   retcode = drmHashLookup(table, key, &retval);
129 
130     switch (retcode) {
131     case -1:
132         printf("Bad magic = 0x%08lx:"
133                " key = %lu, expected = %p, returned = %p\n",
134                table->magic, key, value, retval);
135         break;
136     case 1:
137         printf("Not found: key = %lu, expected = %p, returned = %p\n",
138                key, value, retval);
139         break;
140     case 0:
141         if (value != retval) {
142             printf("Bad value: key = %lu, expected = %p, returned = %p\n",
143                    key, value, retval);
144             retcode = -1;
145         }
146         break;
147     default:
148         printf("Bad retcode = %d: key = %lu, expected = %p, returned = %p\n",
149                retcode, key, value, retval);
150         break;
151     }
152     return retcode;
153 }
154 
155 int main(void)
156 {
157     HashTablePtr  table;
158     unsigned long i;
159     int           ret = 0;
160 
161     printf("\n***** 256 consecutive integers ****\n");
162     table = drmHashCreate();
163     for (i = 0; i < 256; i++)
164         drmHashInsert(table, i, (void *)(i << 16 | i));
165     for (i = 0; i < 256; i++)
166         ret |= check_table(table, i, (void *)(i << 16 | i));
167     compute_dist(table);
168     drmHashDestroy(table);
169 
170     printf("\n***** 1024 consecutive integers ****\n");
171     table = drmHashCreate();
172     for (i = 0; i < 1024; i++)
173         drmHashInsert(table, i, (void *)(i << 16 | i));
174     for (i = 0; i < 1024; i++)
175         ret |= check_table(table, i, (void *)(i << 16 | i));
176     compute_dist(table);
177     drmHashDestroy(table);
178 
179     printf("\n***** 1024 consecutive page addresses (4k pages) ****\n");
180     table = drmHashCreate();
181     for (i = 0; i < 1024; i++)
182         drmHashInsert(table, i*4096, (void *)(i << 16 | i));
183     for (i = 0; i < 1024; i++)
184         ret |= check_table(table, i*4096, (void *)(i << 16 | i));
185     compute_dist(table);
186     drmHashDestroy(table);
187 
188     printf("\n***** 1024 random integers ****\n");
189     table = drmHashCreate();
190     srandom(0xbeefbeef);
191     for (i = 0; i < 1024; i++)
192         drmHashInsert(table, random(), (void *)(i << 16 | i));
193     srandom(0xbeefbeef);
194     for (i = 0; i < 1024; i++)
195         ret |= check_table(table, random(), (void *)(i << 16 | i));
196     srandom(0xbeefbeef);
197     for (i = 0; i < 1024; i++)
198         ret |= check_table(table, random(), (void *)(i << 16 | i));
199     compute_dist(table);
200     drmHashDestroy(table);
201 
202     printf("\n***** 5000 random integers ****\n");
203     table = drmHashCreate();
204     srandom(0xbeefbeef);
205     for (i = 0; i < 5000; i++)
206         drmHashInsert(table, random(), (void *)(i << 16 | i));
207     srandom(0xbeefbeef);
208     for (i = 0; i < 5000; i++)
209         ret |= check_table(table, random(), (void *)(i << 16 | i));
210     srandom(0xbeefbeef);
211     for (i = 0; i < 5000; i++)
212         ret |= check_table(table, random(), (void *)(i << 16 | i));
213     compute_dist(table);
214     drmHashDestroy(table);
215 
216     return ret;
217 }
218