1 /* Fully-inline hash table, used mainly for managing TLS descriptors.
2 Copyright (C) 1999-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 This file is derived from a 2003's version of libiberty's
6 hashtab.c, contributed by Vladimir Makarov (vmakarov@cygnus.com),
7 but with most adaptation points and support for deleting elements
8 removed.
9
10 The GNU C Library is free software; you can redistribute it and/or
11 modify it under the terms of the GNU Lesser General Public
12 License as published by the Free Software Foundation; either
13 version 2.1 of the License, or (at your option) any later version.
14
15 The GNU C Library is distributed in the hope that it will be useful,
16 but WITHOUT ANY WARRANTY; without even the implied warranty of
17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 Lesser General Public License for more details.
19
20 You should have received a copy of the GNU Lesser General Public
21 License along with the GNU C Library; if not, see
22 <https://www.gnu.org/licenses/>. */
23
24 #ifndef INLINE_HASHTAB_H
25 # define INLINE_HASHTAB_H 1
26
27 struct hashtab
28 {
29 /* Table itself. */
30 void **entries;
31
32 /* Current size (in entries) of the hash table */
33 size_t size;
34
35 /* Current number of elements. */
36 size_t n_elements;
37
38 /* Free function for the entries array. This may vary depending on
39 how early the array was allocated. If it is NULL, then the array
40 can't be freed. */
41 void (*free) (void *ptr);
42 };
43
44 inline static struct hashtab *
45 htab_create (void)
46 {
47 struct hashtab *ht = malloc (sizeof (struct hashtab));
48
49 if (! ht)
50 return NULL;
51 ht->size = 3;
52 ht->entries = malloc (sizeof (void *) * ht->size);
53 ht->free = __rtld_free;
54 if (! ht->entries)
55 {
56 free (ht);
57 return NULL;
58 }
59
60 ht->n_elements = 0;
61
62 memset (ht->entries, 0, sizeof (void *) * ht->size);
63
64 return ht;
65 }
66
67 /* This is only called from _dl_unmap, so it's safe to call
68 free(). */
69 inline static void
70 htab_delete (struct hashtab *htab)
71 {
72 int i;
73
74 for (i = htab->size - 1; i >= 0; i--)
75 free (htab->entries[i]);
76
77 htab->free (htab->entries);
78 free (htab);
79 }
80
81 /* Similar to htab_find_slot, but without several unwanted side effects:
82 - Does not call htab->eq_f when it finds an existing entry.
83 - Does not change the count of elements/searches/collisions in the
84 hash table.
85 This function also assumes there are no deleted entries in the table.
86 HASH is the hash value for the element to be inserted. */
87
88 inline static void **
89 find_empty_slot_for_expand (struct hashtab *htab, int hash)
90 {
91 size_t size = htab->size;
92 unsigned int index = hash % size;
93 void **slot = htab->entries + index;
94 int hash2;
95
96 if (! *slot)
97 return slot;
98
99 hash2 = 1 + hash % (size - 2);
100 for (;;)
101 {
102 index += hash2;
103 if (index >= size)
104 index -= size;
105
106 slot = htab->entries + index;
107 if (! *slot)
108 return slot;
109 }
110 }
111
112 /* The following function changes size of memory allocated for the
113 entries and repeatedly inserts the table elements. The occupancy
114 of the table after the call will be about 50%. Naturally the hash
115 table must already exist. Remember also that the place of the
116 table entries is changed. If memory allocation failures are allowed,
117 this function will return zero, indicating that the table could not be
118 expanded. If all goes well, it will return a non-zero value. */
119
120 inline static int
121 htab_expand (struct hashtab *htab, int (*hash_fn) (void *))
122 {
123 void **oentries;
124 void **olimit;
125 void **p;
126 void **nentries;
127 size_t nsize;
128
129 oentries = htab->entries;
130 olimit = oentries + htab->size;
131
132 /* Resize only when table after removal of unused elements is either
133 too full or too empty. */
134 if (htab->n_elements * 2 > htab->size)
135 nsize = _dl_higher_prime_number (htab->n_elements * 2);
136 else
137 nsize = htab->size;
138
139 nentries = calloc (sizeof (void *), nsize);
140 if (nentries == NULL)
141 return 0;
142 htab->entries = nentries;
143 htab->size = nsize;
144
145 p = oentries;
146 do
147 {
148 if (*p)
149 *find_empty_slot_for_expand (htab, hash_fn (*p))
150 = *p;
151
152 p++;
153 }
154 while (p < olimit);
155
156 /* Without recording the free corresponding to the malloc used to
157 allocate the table, we couldn't tell whether this was allocated
158 by the malloc() built into ld.so or the one in the main
159 executable or libc. Calling free() for something that was
160 allocated by the early malloc(), rather than the final run-time
161 malloc() could do Very Bad Things (TM). We will waste memory
162 allocated early as long as there's no corresponding free(), but
163 this isn't so much memory as to be significant. */
164
165 htab->free (oentries);
166
167 /* Use the free() corresponding to the malloc() above to free this
168 up. */
169 htab->free = __rtld_free;
170
171 return 1;
172 }
173
174 /* This function searches for a hash table slot containing an entry
175 equal to the given element. To delete an entry, call this with
176 INSERT = 0, then call htab_clear_slot on the slot returned (possibly
177 after doing some checks). To insert an entry, call this with
178 INSERT = 1, then write the value you want into the returned slot.
179 When inserting an entry, NULL may be returned if memory allocation
180 fails. */
181
182 inline static void **
183 htab_find_slot (struct hashtab *htab, void *ptr, int insert,
184 int (*hash_fn)(void *), int (*eq_fn)(void *, void *))
185 {
186 unsigned int index;
187 int hash, hash2;
188 size_t size;
189 void **entry;
190
191 if (htab->size * 3 <= htab->n_elements * 4
192 && htab_expand (htab, hash_fn) == 0)
193 return NULL;
194
195 hash = hash_fn (ptr);
196
197 size = htab->size;
198 index = hash % size;
199
200 entry = &htab->entries[index];
201 if (!*entry)
202 goto empty_entry;
203 else if (eq_fn (*entry, ptr))
204 return entry;
205
206 hash2 = 1 + hash % (size - 2);
207 for (;;)
208 {
209 index += hash2;
210 if (index >= size)
211 index -= size;
212
213 entry = &htab->entries[index];
214 if (!*entry)
215 goto empty_entry;
216 else if (eq_fn (*entry, ptr))
217 return entry;
218 }
219
220 empty_entry:
221 if (!insert)
222 return NULL;
223
224 htab->n_elements++;
225 return entry;
226 }
227
228 #endif /* INLINE_HASHTAB_H */