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 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 } 104 105 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 } 115 116 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. */ 138 139 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 } 166 167 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 } 179 180 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 } 198 199 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 } 215 216 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 } 232 233 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