libobjc/hash.c

   1 /* Hash tables for Objective C internal structures
   2    Copyright (C) 1993, 1996, 1997, 2004, 2009, 2010
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 3, or (at your option)
  10 any later version.
  11
  12 GCC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 Under Section 7 of GPL version 3, you are granted additional
  18 permissions described in the GCC Runtime Library Exception, version
  19 3.1, as published by the Free Software Foundation.
  20
  21 You should have received a copy of the GNU General Public License and
  22 a copy of the GCC Runtime Library Exception along with this program;
  23 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  24 <http://www.gnu.org/licenses/>.  */
  25
  26 #include "objc-private/common.h"
  27 #include <assert.h>               /* For assert.  */
  28
  29 #include "objc/runtime.h"         /* For objc_calloc.  */
  30 #include "objc-private/hash.h"
  31
  32 /* These two macros determine when a hash table is full and
  33    by how much it should be expanded respectively.
  34
  35    These equations are percentages.  */
  36 #define FULLNESS(cache) \
  37    ((((cache)->size * 75) / 100) <= (cache)->used)
  38 #define EXPANSION(cache) \
  39   ((cache)->size * 2)
  40
  41 cache_ptr
  42 objc_hash_new (unsigned int size, hash_func_type hash_func,
  43                compare_func_type compare_func)
  44 {
  45   cache_ptr cache;
  46
  47   /* Pass me a value greater than 0 and a power of 2.  */
  48   assert (size);
  49   assert (! (size & (size - 1)));
  50
  51   /* Allocate the cache structure.  calloc insures its initialization
  52      for default values.  */
  53   cache = (cache_ptr) objc_calloc (1, sizeof (struct cache));
  54   assert (cache);
  55
  56   /* Allocate the array of buckets for the cache.  calloc initializes
  57      all of the pointers to NULL.  */
  58   cache->node_table
  59     = (node_ptr *) objc_calloc (size, sizeof (node_ptr));
  60   assert (cache->node_table);
  61
  62   cache->size  = size;
  63
  64   /* This should work for all processor architectures (?).  */
  65   cache->mask = (size - 1);
  66
  67   /* Store the hashing function so that codes can be computed.  */
  68   cache->hash_func = hash_func;
  69
  70   /* Store the function that compares hash keys to determine if they
  71      are equal.  */
  72   cache->compare_func = compare_func;
  73
  74   return cache;
  75 }
  76
  77
  78 void
  79 objc_hash_delete (cache_ptr cache)
  80 {
  81   node_ptr node;
  82   node_ptr next_node;
  83   unsigned int i;
  84
  85   /* Purge all key/value pairs from the table.  */
  86   /* Step through the nodes one by one and remove every node WITHOUT
  87      using objc_hash_next. this makes objc_hash_delete much more
  88      efficient. */
  89   for (i = 0; i < cache->size; i++)
  90     {
  91       if ((node = cache->node_table[i]))
  92         {
  93           /* An entry in the hash table has been found.  Now step
  94              through the nodes next in the list and free them.  */
  95           while ((next_node = node->next))
  96             {
  97               objc_hash_remove (cache,node->key);
  98               node = next_node;
  99             }
 100           objc_hash_remove (cache,node->key);
 101         }
 102     }
 103
 104   /* Release the array of nodes and the cache itself.  */
 105   objc_free(cache->node_table);
 106   objc_free(cache);
 107 }
 108
 109
 110 void
 111 objc_hash_add (cache_ptr *cachep, const void *key, void *value)
 112 {
 113   size_t indx = (*(*cachep)->hash_func) (*cachep, key);
 114   node_ptr node = (node_ptr) objc_calloc (1, sizeof (struct cache_node));
 115
 116   assert (node);
 117
 118   /* Initialize the new node.  */
 119   node->key    = key;
 120   node->value  = value;
 121   node->next  = (*cachep)->node_table[indx];
 122
 123   /* Debugging.  Check the list for another key.  */
 124 #ifdef DEBUG
 125   {
 126     node_ptr node1 = (*cachep)->node_table[indx];
 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 to expand if it is
 142      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 primitive
 149          functions thereby increasing its correctness.  */
 150       node_ptr node1 = NULL;
 151       cache_ptr new = objc_hash_new (EXPANSION (*cachep),
 152                                      (*cachep)->hash_func,
 153                                      (*cachep)->compare_func);
 154
 155       DEBUG_PRINTF ("Expanding cache %#x from %d to %d\n",
 156                     (int) *cachep, (*cachep)->size, new->size);
 157
 158       /* Copy the nodes from the first hash table to the new one.  */
 159       while ((node1 = objc_hash_next (*cachep, node1)))
 160         objc_hash_add (&new, node1->key, node1->value);
 161
 162       /* Trash the old cache.  */
 163       objc_hash_delete (*cachep);
 164
 165       /* Return a pointer to the new hash table.  */
 166       *cachep = new;
 167     }
 168 }
 169
 170 void
 171 objc_hash_remove (cache_ptr cache, const void *key)
 172 {
 173   size_t indx = (*cache->hash_func) (cache, key);
 174   node_ptr node = cache->node_table[indx];
 175
 176   /* We assume there is an entry in the table.  Error if it is
 177      not.  */
 178   assert (node);
 179
 180   /* Special case.  First element is the key/value pair to be
 181      removed.  */
 182   if ((*cache->compare_func) (node->key, key))
 183     {
 184       cache->node_table[indx] = node->next;
 185       objc_free(node);
 186     }
 187   else
 188     {
 189       /* Otherwise, find the hash entry.  */
 190       node_ptr prev = node;
 191       BOOL removed = NO;
 192       do
 193         {
 194           if ((*cache->compare_func) (node->key, key))
 195             {
 196               prev->next = node->next, removed = YES;
 197               objc_free(node);
 198             }
 199           else
 200             prev = node, node = node->next;
 201         }
 202       while (!removed && node);
 203       assert (removed);
 204     }
 205
 206   /* Decrement the number of entries in the hash table.  */
 207   --cache->used;
 208 }
 209
 210
 211 node_ptr
 212 objc_hash_next (cache_ptr cache, node_ptr node)
 213 {
 214   /* If the scan is being started then reset the last node visitied
 215      pointer and bucket index.  */
 216   if (!node)
 217     cache->last_bucket  = 0;
 218
 219   /* If there is a node visited last then check for another entry in
 220      the same bucket.  Otherwise step to the next bucket.  */
 221   if (node)
 222     {
 223       if (node->next)
 224         {
 225           /* There is a node which follows the last node returned.
 226              Step to that node and retun it.  */
 227           return node->next;
 228         }
 229       else
 230         ++cache->last_bucket;
 231   }
 232
 233   /* If the list isn't exhausted then search the buckets for other
 234      nodes.  */
 235   if (cache->last_bucket < cache->size)
 236     {
 237       /*  Scan the remainder of the buckets looking for an entry at
 238           the head of the list.  Return the first item found.  */
 239       while (cache->last_bucket < cache->size)
 240         if (cache->node_table[cache->last_bucket])
 241           return cache->node_table[cache->last_bucket];
 242         else
 243           ++cache->last_bucket;
 244
 245       /* No further nodes were found in the hash table.  */
 246       return NULL;
 247     }
 248   else
 249     return NULL;
 250 }
 251
 252
 253 /* Given KEY, return corresponding value for it in CACHE.  Return NULL
 254    if the KEY is not recorded.  */
 255 void *
 256 objc_hash_value_for_key (cache_ptr cache, const void *key)
 257 {
 258   node_ptr node = cache->node_table[(*cache->hash_func) (cache, key)];
 259   void *retval = NULL;
 260
 261   if (node)
 262     do
 263       {
 264         if ((*cache->compare_func) (node->key, key))
 265           {
 266             retval = node->value;
 267             break;
 268           }
 269         else
 270           node = node->next;
 271       }
 272     while (! retval && node);
 273
 274   return retval;
 275 }
 276
 277 /* Given KEY, return YES if it exists in the CACHE.  Return NO if it
 278    does not */
 279 BOOL
 280 objc_hash_is_key_in_hash (cache_ptr cache, const void *key)
 281 {
 282   node_ptr node = cache->node_table[(*cache->hash_func) (cache, key)];
 283
 284   if (node)
 285     do
 286       {
 287         if ((*cache->compare_func)(node->key, key))
 288           return YES;
 289         else
 290           node = node->next;
 291       }
 292     while (node);
 293
 294   return NO;
 295 }