xf86drmHash.c

   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 }