libobjc/hash.c

   1 /* Hash tables for Objective C internal structures
   2    Copyright (C) 1993, 1996, 1997 Free Software Foundation, Inc.
   3
   4 This file is part of GNU CC.
   5
   6 GNU CC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU CC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU CC; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 59 Temple Place - Suite 330,
  19 Boston, MA 02111-1307, USA.  */
  20
  21 /* As a special exception, if you link this library with files
  22    compiled with GCC to produce an executable, this does not cause
  23    the resulting executable to be covered by the GNU General Public License.
  24    This exception does not however invalidate any other reasons why
  25    the executable file might be covered by the GNU General Public License.  */
  26
  27 #include "assert.h"
  28
  29 #include "hash.h"
  30
  31 #include "runtime.h"            /* for DEBUG_PRINTF */
  32
  33 /* These two macros determine when a hash table is full and
  34    by how much it should be expanded respectively.
  35
  36    These equations are percentages.  */
  37 #define FULLNESS(cache) \
  38    ((((cache)->size * 75) / 100) <= (cache)->used)
  39 #define EXPANSION(cache) \
  40   ((cache)->size * 2)
  41
  42 cache_ptr
  43 hash_new (unsigned int size, hash_func_type hash_func,
  44           compare_func_type compare_func)
  45 {
  46   cache_ptr cache;
  47
  48   /* Pass me a value greater than 0 and a power of 2.  */
  49   assert (size);
  50   assert (!(size & (size - 1)));
  51
  52   /* Allocate the cache structure.  calloc insures
  53      its initialization for default values.  */
  54   cache = (cache_ptr) objc_calloc (1, sizeof (struct cache));
  55   assert (cache);
  56
  57   /* Allocate the array of buckets for the cache.
  58      calloc initializes all of the pointers to NULL.  */
  59   cache->node_table
  60     = (node_ptr *) objc_calloc (size, sizeof (node_ptr));
  61   assert (cache->node_table);
  62
  63   cache->size  = size;
  64
  65   /* This should work for all processor architectures? */
  66   cache->mask = (size - 1);
  67
  68   /* Store the hashing function so that codes can be computed.  */
  69   cache->hash_func = hash_func;
  70
  71   /* Store the function that compares hash keys to
  72      determine if they are equal.  */
  73   cache->compare_func = compare_func;
  74
  75   return cache;
  76 }
  77
  78
  79 void
  80 hash_delete (cache_ptr cache)
  81 {
  82   node_ptr node;
  83   node_ptr next_node;
  84   unsigned int i;
  85
  86   /* Purge all key/value pairs from the table.  */
  87   /* Step through the nodes one by one and remove every node WITHOUT
  88      using hash_next. this makes hash_delete much more efficient. */
  89   for (i = 0;i < cache->size;i++) {
  90     if ((node = cache->node_table[i])) {
  91       /* an entry in the hash table has been found, now step through the
  92          nodes next in the list and free them. */
  93       while ((next_node = node->next)) {
  94         hash_remove (cache,node->key);
  95         node = next_node;
  96       }
  97
  98       hash_remove (cache,node->key);
  99     }
 100   }
 101
 102   /* Release the array of nodes and the cache itself.  */
 103   objc_free(cache->node_table);
 104   objc_free(cache);
 105 }
 106
 107
 108 void
 109 hash_add (cache_ptr *cachep, const void *key, void *value)
 110 {
 111   size_t indx = (*(*cachep)->hash_func)(*cachep, key);
 112   node_ptr node = (node_ptr) objc_calloc (1, sizeof (struct cache_node));
 113
 114
 115   assert (node);
 116
 117   /* Initialize the new node.  */
 118   node->key    = key;
 119   node->value  = value;
 120   node->next  = (*cachep)->node_table[indx];
 121
 122   /* Debugging.
 123      Check the list for another key.  */
 124 #ifdef DEBUG
 125   { node_ptr node1 = (*cachep)->node_table[indx];
 126
 127     while (node1) {
 128
 129       assert (node1->key != key);
 130       node1 = node1->next;
 131     }
 132   }
 133 #endif
 134
 135   /* Install the node as the first element on the list.  */
 136   (*cachep)->node_table[indx] = node;
 137
 138   /* Bump the number of entries in the cache.  */
 139   ++(*cachep)->used;
 140
 141   /* Check the hash table's fullness.   We're going
 142      to expand if it is above the fullness level.  */
 143   if (FULLNESS (*cachep)) {
 144
 145     /* The hash table has reached its fullness level.  Time to
 146        expand it.
 147
 148        I'm using a slow method here but is built on other
 149        primitive functions thereby increasing its
 150        correctness.  */
 151     node_ptr node1 = NULL;
 152     cache_ptr new = hash_new (EXPANSION (*cachep),
 153                               (*cachep)->hash_func,
 154                               (*cachep)->compare_func);
 155
 156     DEBUG_PRINTF ("Expanding cache %#x from %d to %d\n",
 157                   *cachep, (*cachep)->size, new->size);
 158
 159     /* Copy the nodes from the first hash table to the new one.  */
 160     while ((node1 = hash_next (*cachep, node1)))
 161       hash_add (&new, node1->key, node1->value);
 162
 163     /* Trash the old cache.  */
 164     hash_delete (*cachep);
 165
 166     /* Return a pointer to the new hash table.  */
 167     *cachep = new;
 168   }
 169 }
 170
 171
 172 void
 173 hash_remove (cache_ptr cache, const void *key)
 174 {
 175   size_t indx = (*cache->hash_func)(cache, key);
 176   node_ptr node = cache->node_table[indx];
 177
 178
 179   /* We assume there is an entry in the table.  Error if it is not.  */
 180   assert (node);
 181
 182   /* Special case.  First element is the key/value pair to be removed.  */
 183   if ((*cache->compare_func)(node->key, key)) {
 184     cache->node_table[indx] = node->next;
 185     objc_free(node);
 186   } else {
 187
 188     /* Otherwise, find the hash entry.  */
 189     node_ptr prev = node;
 190     BOOL removed = NO;
 191
 192     do {
 193
 194       if ((*cache->compare_func)(node->key, key)) {
 195         prev->next = node->next, removed = YES;
 196         objc_free(node);
 197       } else
 198         prev = node, node = node->next;
 199     } while (!removed && node);
 200     assert (removed);
 201   }
 202
 203   /* Decrement the number of entries in the hash table.  */
 204   --cache->used;
 205 }
 206
 207
 208 node_ptr
 209 hash_next (cache_ptr cache, node_ptr node)
 210 {
 211   /* If the scan is being started then reset the last node
 212      visitied pointer and bucket index.  */
 213   if (!node)
 214     cache->last_bucket  = 0;
 215
 216   /* If there is a node visited last then check for another
 217      entry in the same bucket;  Otherwise step to the next bucket.  */
 218   if (node) {
 219     if (node->next)
 220       /* There is a node which follows the last node
 221          returned.  Step to that node and retun it.  */
 222       return node->next;
 223     else
 224       ++cache->last_bucket;
 225   }
 226
 227   /* If the list isn't exhausted then search the buckets for
 228      other nodes.  */
 229   if (cache->last_bucket < cache->size) {
 230     /*  Scan the remainder of the buckets looking for an entry
 231         at the head of the list.  Return the first item found.  */
 232     while (cache->last_bucket < cache->size)
 233       if (cache->node_table[cache->last_bucket])
 234         return cache->node_table[cache->last_bucket];
 235       else
 236         ++cache->last_bucket;
 237
 238     /* No further nodes were found in the hash table.  */
 239     return NULL;
 240   } else
 241     return NULL;
 242 }
 243
 244
 245 /* Given KEY, return corresponding value for it in CACHE.
 246    Return NULL if the KEY is not recorded.  */
 247
 248 void *
 249 hash_value_for_key (cache_ptr cache, const void *key)
 250 {
 251   node_ptr node = cache->node_table[(*cache->hash_func)(cache, key)];
 252   void *retval = NULL;
 253
 254   if (node)
 255     do {
 256       if ((*cache->compare_func)(node->key, key)) {
 257         retval = node->value;
 258               break;
 259       } else
 260         node = node->next;
 261     } while (!retval && node);
 262
 263   return retval;
 264 }
 265
 266 /* Given KEY, return YES if it exists in the CACHE.
 267    Return NO if it does not */
 268
 269 BOOL
 270 hash_is_key_in_hash (cache_ptr cache, const void *key)
 271 {
 272   node_ptr node = cache->node_table[(*cache->hash_func)(cache, key)];
 273
 274   if (node)
 275     do {
 276       if ((*cache->compare_func)(node->key, key))
 277           return YES;
 278       else
 279         node = node->next;
 280     } while (node);
 281
 282   return NO;
 283 }