1 /* Hash tables for Objective C internal structures
2 Copyright (C) 1993-2023 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 }