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1/* Fully-inline hash table, used mainly for managing TLS descriptors.
2 Copyright (C) 1999-2019 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Alexandre Oliva <aoliva@redhat.com>
5
6 This file is derived from a 2003's version of libiberty's
7 hashtab.c, contributed by Vladimir Makarov (vmakarov@cygnus.com),
8 but with most adaptation points and support for deleting elements
9 removed.
10
11 The GNU C Library is free software; you can redistribute it and/or
12 modify it under the terms of the GNU Lesser General Public
13 License as published by the Free Software Foundation; either
14 version 2.1 of the License, or (at your option) any later version.
15
16 The GNU C Library is distributed in the hope that it will be useful,
17 but WITHOUT ANY WARRANTY; without even the implied warranty of
18 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 Lesser General Public License for more details.
20
21 You should have received a copy of the GNU Lesser General Public
22 License along with the GNU C Library; if not, see
23 <http://www.gnu.org/licenses/>. */
24
25#ifndef INLINE_HASHTAB_H
26# define INLINE_HASHTAB_H 1
27
28extern void weak_function free (void *ptr);
29
30struct hashtab
31{
32 /* Table itself. */
33 void **entries;
34
35 /* Current size (in entries) of the hash table */
36 size_t size;
37
38 /* Current number of elements. */
39 size_t n_elements;
40
41 /* Free function for the entries array. This may vary depending on
42 how early the array was allocated. If it is NULL, then the array
43 can't be freed. */
44 void (*free) (void *ptr);
45};
46
47inline static struct hashtab *
48htab_create (void)
49{
50 struct hashtab *ht = malloc (sizeof (struct hashtab));
51
52 if (! ht)
53 return NULL;
54 ht->size = 3;
55 ht->entries = malloc (sizeof (void *) * ht->size);
56 ht->free = free;
57 if (! ht->entries)
58 {
59 if (ht->free)
60 ht->free (ht);
61 return NULL;
62 }
63
64 ht->n_elements = 0;
65
66 memset (ht->entries, 0, sizeof (void *) * ht->size);
67
68 return ht;
69}
70
71/* This is only called from _dl_unmap, so it's safe to call
72 free(). */
73inline static void
74htab_delete (struct hashtab *htab)
75{
76 int i;
77
78 for (i = htab->size - 1; i >= 0; i--)
79 free (htab->entries[i]);
80
81 if (htab->free)
82 htab->free (htab->entries);
83 free (htab);
84}
85
86/* Similar to htab_find_slot, but without several unwanted side effects:
87 - Does not call htab->eq_f when it finds an existing entry.
88 - Does not change the count of elements/searches/collisions in the
89 hash table.
90 This function also assumes there are no deleted entries in the table.
91 HASH is the hash value for the element to be inserted. */
92
93inline static void **
94find_empty_slot_for_expand (struct hashtab *htab, int hash)
95{
96 size_t size = htab->size;
97 unsigned int index = hash % size;
98 void **slot = htab->entries + index;
99 int hash2;
100
101 if (! *slot)
102 return slot;
103
104 hash2 = 1 + hash % (size - 2);
105 for (;;)
106 {
107 index += hash2;
108 if (index >= size)
109 index -= size;
110
111 slot = htab->entries + index;
112 if (! *slot)
113 return slot;
114 }
115}
116
117/* The following function changes size of memory allocated for the
118 entries and repeatedly inserts the table elements. The occupancy
119 of the table after the call will be about 50%. Naturally the hash
120 table must already exist. Remember also that the place of the
121 table entries is changed. If memory allocation failures are allowed,
122 this function will return zero, indicating that the table could not be
123 expanded. If all goes well, it will return a non-zero value. */
124
125inline static int
126htab_expand (struct hashtab *htab, int (*hash_fn) (void *))
127{
128 void **oentries;
129 void **olimit;
130 void **p;
131 void **nentries;
132 size_t nsize;
133
134 oentries = htab->entries;
135 olimit = oentries + htab->size;
136
137 /* Resize only when table after removal of unused elements is either
138 too full or too empty. */
139 if (htab->n_elements * 2 > htab->size)
140 nsize = _dl_higher_prime_number (htab->n_elements * 2);
141 else
142 nsize = htab->size;
143
144 nentries = calloc (sizeof (void *), nsize);
145 if (nentries == NULL)
146 return 0;
147 htab->entries = nentries;
148 htab->size = nsize;
149
150 p = oentries;
151 do
152 {
153 if (*p)
154 *find_empty_slot_for_expand (htab, hash_fn (*p))
155 = *p;
156
157 p++;
158 }
159 while (p < olimit);
160
161 /* Without recording the free corresponding to the malloc used to
162 allocate the table, we couldn't tell whether this was allocated
163 by the malloc() built into ld.so or the one in the main
164 executable or libc. Calling free() for something that was
165 allocated by the early malloc(), rather than the final run-time
166 malloc() could do Very Bad Things (TM). We will waste memory
167 allocated early as long as there's no corresponding free(), but
168 this isn't so much memory as to be significant. */
169
170 if (htab->free)
171 htab->free (oentries);
172
173 /* Use the free() corresponding to the malloc() above to free this
174 up. */
175 htab->free = free;
176
177 return 1;
178}
179
180/* This function searches for a hash table slot containing an entry
181 equal to the given element. To delete an entry, call this with
182 INSERT = 0, then call htab_clear_slot on the slot returned (possibly
183 after doing some checks). To insert an entry, call this with
184 INSERT = 1, then write the value you want into the returned slot.
185 When inserting an entry, NULL may be returned if memory allocation
186 fails. */
187
188inline static void **
189htab_find_slot (struct hashtab *htab, void *ptr, int insert,
190 int (*hash_fn)(void *), int (*eq_fn)(void *, void *))
191{
192 unsigned int index;
193 int hash, hash2;
194 size_t size;
195 void **entry;
196
197 if (htab->size * 3 <= htab->n_elements * 4
198 && htab_expand (htab, hash_fn) == 0)
199 return NULL;
200
201 hash = hash_fn (ptr);
202
203 size = htab->size;
204 index = hash % size;
205
206 entry = &htab->entries[index];
207 if (!*entry)
208 goto empty_entry;
209 else if (eq_fn (*entry, ptr))
210 return entry;
211
212 hash2 = 1 + hash % (size - 2);
213 for (;;)
214 {
215 index += hash2;
216 if (index >= size)
217 index -= size;
218
219 entry = &htab->entries[index];
220 if (!*entry)
221 goto empty_entry;
222 else if (eq_fn (*entry, ptr))
223 return entry;
224 }
225
226 empty_entry:
227 if (!insert)
228 return NULL;
229
230 htab->n_elements++;
231 return entry;
232}
233
234#endif /* INLINE_HASHTAB_H */
235

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