libobjc/hash.c

   1 /* Hash tables for Objective C internal structures
   2    Copyright (C) 1993-2020 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC 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 3, or (at your option)
   9 any later version.
  10
  11 GCC 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 Under Section 7 of GPL version 3, you are granted additional
  17 permissions described in the GCC Runtime Library Exception, version
  18 3.1, as published by the Free Software Foundation.
  19
  20 You should have received a copy of the GNU General Public License and
  21 a copy of the GCC Runtime Library Exception along with this program;
  22 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 <http://www.gnu.org/licenses/>.  */
  24
  25 #include "objc-private/common.h"
  26 #include <assert.h>               /* For assert.  */
  27
  28 #include "objc/runtime.h"         /* For objc_calloc.  */
  29 #include "objc-private/hash.h"
  30
  31 /* These two macros determine when a hash table is full and
  32    by how much it should be expanded respectively.
  33
  34    These equations are percentages.  */
  35 #define FULLNESS(cache) \
  36    ((((cache)->size * 75) / 100) <= (cache)->used)
  37 #define EXPANSION(cache) \
  38   ((cache)->size * 2)
  39
  40 cache_ptr
  41 objc_hash_new (unsigned int size, hash_func_type hash_func,
  42                compare_func_type compare_func)
  43 {
  44   cache_ptr cache;
  45
  46   /* Pass me a value greater than 0 and a power of 2.  */
  47   assert (size);
  48   assert (! (size & (size - 1)));
  49
  50   /* Allocate the cache structure.  calloc insures its initialization
  51      for default values.  */
  52   cache = (cache_ptr) objc_calloc (1, sizeof (struct cache));
  53   assert (cache);
  54
  55   /* Allocate the array of buckets for the cache.  calloc initializes
  56      all of the pointers to NULL.  */
  57   cache->node_table
  58     = (node_ptr *) objc_calloc (size, sizeof (node_ptr));
  59   assert (cache->node_table);
  60
  61   cache->size  = size;
  62
  63   /* This should work for all processor architectures (?).  */
  64   cache->mask = (size - 1);
  65
  66   /* Store the hashing function so that codes can be computed.  */
  67   cache->hash_func = hash_func;
  68
  69   /* Store the function that compares hash keys to determine if they
  70      are equal.  */
  71   cache->compare_func = compare_func;
  72
  73   return cache;
  74 }
  75
  76
  77 void
  78 objc_hash_delete (cache_ptr cache)
  79 {
  80   node_ptr node;
  81   node_ptr next_node;
  82   unsigned int i;
  83
  84   /* Purge all key/value pairs from the table.  */
  85   /* Step through the nodes one by one and remove every node WITHOUT
  86      using objc_hash_next. this makes objc_hash_delete much more
  87      efficient. */
  88   for (i = 0; i < cache->size; i++)
  89     {
  90       if ((node = cache->node_table[i]))
  91         {
  92           /* An entry in the hash table has been found.  Now step
  93              through the nodes next in the list and free them.  */
  94           while ((next_node = node->next))
  95             {
  96               objc_hash_remove (cache,node->key);
  97               node = next_node;
  98             }
  99           objc_hash_remove (cache,node->key);
 100         }
 101     }
 102
 103   /* Release the array of nodes and the cache itself.  */
 104   objc_free(cache->node_table);
 105   objc_free(cache);
 106 }
 107
 108
 109 void
 110 objc_hash_add (cache_ptr *cachep, const void *key, void *value)
 111 {
 112   size_t indx = (*(*cachep)->hash_func) (*cachep, key);
 113   node_ptr node = (node_ptr) objc_calloc (1, sizeof (struct cache_node));
 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.  Check the list for another key.  */
 123 #ifdef DEBUG
 124   {
 125     node_ptr node1 = (*cachep)->node_table[indx];
 126     while (node1)
 127       {
 128         assert (node1->key != key);
 129         node1 = node1->next;
 130       }
 131   }
 132 #endif
 133
 134   /* Install the node as the first element on the list.  */
 135   (*cachep)->node_table[indx] = node;
 136
 137   /* Bump the number of entries in the cache.  */
 138   ++(*cachep)->used;
 139
 140   /* Check the hash table's fullness.  We're going to expand if it is
 141      above the fullness level.  */
 142   if (FULLNESS (*cachep))
 143     {
 144       /* The hash table has reached its fullness level.  Time to
 145          expand it.
 146
 147          I'm using a slow method here but is built on other primitive
 148          functions thereby increasing its correctness.  */
 149       node_ptr node1 = NULL;
 150       cache_ptr new = objc_hash_new (EXPANSION (*cachep),
 151                                      (*cachep)->hash_func,
 152                                      (*cachep)->compare_func);
 153
 154       DEBUG_PRINTF ("Expanding cache %#x from %d to %d\n",
 155                     (int) *cachep, (*cachep)->size, new->size);
 156
 157       /* Copy the nodes from the first hash table to the new one.  */
 158       while ((node1 = objc_hash_next (*cachep, node1)))
 159         objc_hash_add (&new, node1->key, node1->value);
 160
 161       /* Trash the old cache.  */
 162       objc_hash_delete (*cachep);
 163
 164       /* Return a pointer to the new hash table.  */
 165       *cachep = new;
 166     }
 167 }
 168
 169 void
 170 objc_hash_remove (cache_ptr cache, const void *key)
 171 {
 172   size_t indx = (*cache->hash_func) (cache, key);
 173   node_ptr node = cache->node_table[indx];
 174
 175   /* We assume there is an entry in the table.  Error if it is
 176      not.  */
 177   assert (node);
 178
 179   /* Special case.  First element is the key/value pair to be
 180      removed.  */
 181   if ((*cache->compare_func) (node->key, key))
 182     {
 183       cache->node_table[indx] = node->next;
 184       objc_free(node);
 185     }
 186   else
 187     {
 188       /* Otherwise, find the hash entry.  */
 189       node_ptr prev = node;
 190       BOOL removed = NO;
 191       do
 192         {
 193           if ((*cache->compare_func) (node->key, key))
 194             {
 195               prev->next = node->next, removed = YES;
 196               objc_free(node);
 197             }
 198           else
 199             prev = node, node = node->next;
 200         }
 201       while (!removed && node);
 202       assert (removed);
 203     }
 204
 205   /* Decrement the number of entries in the hash table.  */
 206   --cache->used;
 207 }
 208
 209
 210 node_ptr
 211 objc_hash_next (cache_ptr cache, node_ptr node)
 212 {
 213   /* If the scan is being started then reset the last node visitied
 214      pointer and bucket index.  */
 215   if (!node)
 216     cache->last_bucket  = 0;
 217
 218   /* If there is a node visited last then check for another entry in
 219      the same bucket.  Otherwise step to the next bucket.  */
 220   if (node)
 221     {
 222       if (node->next)
 223         {
 224           /* There is a node which follows the last node returned.
 225              Step to that node and retun it.  */
 226           return node->next;
 227         }
 228       else
 229         ++cache->last_bucket;
 230   }
 231
 232   /* If the list isn't exhausted then search the buckets for other
 233      nodes.  */
 234   if (cache->last_bucket < cache->size)
 235     {
 236       /*  Scan the remainder of the buckets looking for an entry at
 237           the head of the list.  Return the first item found.  */
 238       while (cache->last_bucket < cache->size)
 239         if (cache->node_table[cache->last_bucket])
 240           return cache->node_table[cache->last_bucket];
 241         else
 242           ++cache->last_bucket;
 243
 244       /* No further nodes were found in the hash table.  */
 245       return NULL;
 246     }
 247   else
 248     return NULL;
 249 }
 250
 251
 252 /* Given KEY, return corresponding value for it in CACHE.  Return NULL
 253    if the KEY is not recorded.  */
 254 void *
 255 objc_hash_value_for_key (cache_ptr cache, const void *key)
 256 {
 257   node_ptr node = cache->node_table[(*cache->hash_func) (cache, key)];
 258   void *retval = NULL;
 259
 260   if (node)
 261     do
 262       {
 263         if ((*cache->compare_func) (node->key, key))
 264           {
 265             retval = node->value;
 266             break;
 267           }
 268         else
 269           node = node->next;
 270       }
 271     while (! retval && node);
 272
 273   return retval;
 274 }
 275
 276 /* Given KEY, return YES if it exists in the CACHE.  Return NO if it
 277    does not */
 278 BOOL
 279 objc_hash_is_key_in_hash (cache_ptr cache, const void *key)
 280 {
 281   node_ptr node = cache->node_table[(*cache->hash_func) (cache, key)];
 282
 283   if (node)
 284     do
 285       {
 286         if ((*cache->compare_func)(node->key, key))
 287           return YES;
 288         else
 289           node = node->next;
 290       }
 291     while (node);
 292
 293   return NO;
 294 }