1 /* xf86drmHash.c -- Small hash table support for integer -> integer mapping 2 * Created: Sun Apr 18 09:35:45 1999 by faith (at) 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 (at) 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 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 return hash; 102 } 103 104 void *drmHashCreate(void) 105 { 106 HashTablePtr table; 107 int i; 108 109 table = drmMalloc(sizeof(*table)); 110 if (!table) return NULL; 111 table->magic = HASH_MAGIC; 112 table->entries = 0; 113 table->hits = 0; 114 table->partials = 0; 115 table->misses = 0; 116 117 for (i = 0; i < HASH_SIZE; i++) table->buckets[i] = NULL; 118 return table; 119 } 120 121 int drmHashDestroy(void *t) 122 { 123 HashTablePtr table = (HashTablePtr)t; 124 HashBucketPtr bucket; 125 HashBucketPtr next; 126 int i; 127 128 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */ 129 130 for (i = 0; i < HASH_SIZE; i++) { 131 for (bucket = table->buckets[i]; bucket;) { 132 next = bucket->next; 133 drmFree(bucket); 134 bucket = next; 135 } 136 } 137 drmFree(table); 138 return 0; 139 } 140 141 /* Find the bucket and organize the list so that this bucket is at the 142 top. */ 143 144 static HashBucketPtr HashFind(HashTablePtr table, 145 unsigned long key, unsigned long *h) 146 { 147 unsigned long hash = HashHash(key); 148 HashBucketPtr prev = NULL; 149 HashBucketPtr bucket; 150 151 if (h) *h = hash; 152 153 for (bucket = table->buckets[hash]; bucket; bucket = bucket->next) { 154 if (bucket->key == key) { 155 if (prev) { 156 /* Organize */ 157 prev->next = bucket->next; 158 bucket->next = table->buckets[hash]; 159 table->buckets[hash] = bucket; 160 ++table->partials; 161 } else { 162 ++table->hits; 163 } 164 return bucket; 165 } 166 prev = bucket; 167 } 168 ++table->misses; 169 return NULL; 170 } 171 172 int drmHashLookup(void *t, unsigned long key, void **value) 173 { 174 HashTablePtr table = (HashTablePtr)t; 175 HashBucketPtr bucket; 176 177 if (!table || table->magic != HASH_MAGIC) return -1; /* Bad magic */ 178 179 bucket = HashFind(table, key, NULL); 180 if (!bucket) return 1; /* Not found */ 181 *value = bucket->value; 182 return 0; /* Found */ 183 } 184 185 int drmHashInsert(void *t, unsigned long key, void *value) 186 { 187 HashTablePtr table = (HashTablePtr)t; 188 HashBucketPtr bucket; 189 unsigned long hash; 190 191 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */ 192 193 if (HashFind(table, key, &hash)) return 1; /* Already in table */ 194 195 bucket = drmMalloc(sizeof(*bucket)); 196 if (!bucket) return -1; /* Error */ 197 bucket->key = key; 198 bucket->value = value; 199 bucket->next = table->buckets[hash]; 200 table->buckets[hash] = bucket; 201 return 0; /* Added to table */ 202 } 203 204 int drmHashDelete(void *t, unsigned long key) 205 { 206 HashTablePtr table = (HashTablePtr)t; 207 unsigned long hash; 208 HashBucketPtr bucket; 209 210 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */ 211 212 bucket = HashFind(table, key, &hash); 213 214 if (!bucket) return 1; /* Not found */ 215 216 table->buckets[hash] = bucket->next; 217 drmFree(bucket); 218 return 0; 219 } 220 221 int drmHashNext(void *t, unsigned long *key, void **value) 222 { 223 HashTablePtr table = (HashTablePtr)t; 224 225 while (table->p0 < HASH_SIZE) { 226 if (table->p1) { 227 *key = table->p1->key; 228 *value = table->p1->value; 229 table->p1 = table->p1->next; 230 return 1; 231 } 232 table->p1 = table->buckets[table->p0]; 233 ++table->p0; 234 } 235 return 0; 236 } 237 238 int drmHashFirst(void *t, unsigned long *key, void **value) 239 { 240 HashTablePtr table = (HashTablePtr)t; 241 242 if (table->magic != HASH_MAGIC) return -1; /* Bad magic */ 243 244 table->p0 = 0; 245 table->p1 = table->buckets[0]; 246 return drmHashNext(table, key, value); 247 } 248