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a2f945c6 VM |
1 | /* An expandable hash tables datatype. |
2 | Copyright (C) 1999 Free Software Foundation, Inc. | |
3 | Contributed by Vladimir Makarov (vmakarov@cygnus.com). | |
4 | ||
5 | This file is part of the libiberty library. | |
6 | Libiberty is free software; you can redistribute it and/or | |
7 | modify it under the terms of the GNU Library General Public | |
8 | License as published by the Free Software Foundation; either | |
9 | version 2 of the License, or (at your option) any later version. | |
10 | ||
11 | Libiberty 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 GNU | |
14 | Library General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU Library General Public | |
17 | License along with libiberty; see the file COPYING.LIB. If | |
18 | not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, | |
19 | Boston, MA 02111-1307, USA. */ | |
20 | ||
21 | /* This package implements basic hash table functionality. It is possible | |
22 | to search for an entry, create an entry and destroy an entry. | |
23 | ||
24 | Elements in the table are generic pointers. | |
25 | ||
26 | The size of the table is not fixed; if the occupancy of the table | |
27 | grows too high the hash table will be expanded. | |
28 | ||
29 | The abstract data implementation is based on generalized Algorithm D | |
30 | from Knuth's book "The art of computer programming". Hash table is | |
31 | expanded by creation of new hash table and transferring elements from | |
32 | the old table to the new table. */ | |
33 | ||
34 | #ifdef HAVE_CONFIG_H | |
35 | #include "config.h" | |
36 | #endif | |
37 | ||
38 | #ifdef HAVE_STDLIB_H | |
39 | #include <stdlib.h> | |
40 | #endif | |
41 | ||
42 | #include "libiberty.h" | |
43 | #include "hashtab.h" | |
44 | ||
45 | /* The following variable is used for debugging. Its value is number | |
46 | of all calls of `find_hash_table_entry' for all hash tables. */ | |
47 | ||
48 | static int all_searches = 0; | |
49 | ||
50 | /* The following variable is used for debugging. Its value is number | |
51 | of collisions fixed for time of work with all hash tables. */ | |
52 | ||
53 | static int all_collisions = 0; | |
54 | ||
55 | /* The following variable is used for debugging. Its value is number | |
56 | of all table expansions fixed for time of work with all hash | |
57 | tables. */ | |
58 | ||
59 | static int all_expansions = 0; | |
60 | ||
61 | /* This macro defines reserved value for empty table entry. */ | |
62 | ||
63 | #define EMPTY_ENTRY NULL | |
64 | ||
65 | /* This macro defines reserved value for table entry which contained | |
66 | a deleted element. */ | |
67 | ||
68 | #define DELETED_ENTRY ((void *) 1) | |
69 | ||
70 | /* The following function returns the nearest prime number which is | |
71 | greater than given source number. */ | |
72 | ||
73 | static unsigned long | |
74 | higher_prime_number (number) | |
75 | unsigned long number; | |
76 | { | |
77 | unsigned long i; | |
78 | ||
79 | for (number = (number / 2) * 2 + 3;; number += 2) | |
80 | { | |
81 | for (i = 3; i * i <= number; i += 2) | |
82 | if (number % i == 0) | |
83 | break; | |
84 | if (i * i > number) | |
85 | return number; | |
86 | } | |
87 | } | |
88 | ||
89 | /* This function creates table with length slightly longer than given | |
90 | source length. Created hash table is initiated as empty (all the | |
91 | hash table entries are EMPTY_ENTRY). The function returns the | |
92 | created hash table. */ | |
93 | ||
94 | hash_table_t | |
95 | create_hash_table (size, hash_function, eq_function) | |
96 | size_t size; | |
97 | unsigned (*hash_function) PARAMS ((hash_table_entry_t)); | |
98 | int (*eq_function) PARAMS ((hash_table_entry_t, hash_table_entry_t)); | |
99 | { | |
100 | hash_table_t result; | |
101 | ||
102 | size = higher_prime_number (size); | |
103 | result = (hash_table_t) xmalloc (sizeof (*result)); | |
104 | result->entries | |
105 | = (hash_table_entry_t *) xmalloc (size * sizeof (hash_table_entry_t)); | |
106 | result->size = size; | |
107 | result->hash_function = hash_function; | |
108 | result->eq_function = eq_function; | |
109 | result->number_of_elements = 0; | |
110 | result->number_of_deleted_elements = 0; | |
111 | result->searches = 0; | |
112 | result->collisions = 0; | |
113 | memset (result->entries, 0, size * sizeof (hash_table_entry_t)); | |
114 | return result; | |
115 | } | |
116 | ||
117 | /* This function frees all memory allocated for given hash table. | |
118 | Naturally the hash table must already exist. */ | |
119 | ||
120 | void | |
121 | delete_hash_table (htab) | |
122 | hash_table_t htab; | |
123 | { | |
124 | free (htab->entries); | |
125 | free (htab); | |
126 | } | |
127 | ||
128 | /* This function clears all entries in the given hash table. */ | |
129 | ||
130 | void | |
131 | empty_hash_table (htab) | |
132 | hash_table_t htab; | |
133 | { | |
134 | memset (htab->entries, 0, htab->size * sizeof (hash_table_entry_t)); | |
135 | } | |
136 | ||
137 | /* The following function changes size of memory allocated for the | |
138 | entries and repeatedly inserts the table elements. The occupancy | |
139 | of the table after the call will be about 50%. Naturally the hash | |
140 | table must already exist. Remember also that the place of the | |
141 | table entries is changed. */ | |
142 | ||
143 | static void | |
144 | expand_hash_table (htab) | |
145 | hash_table_t htab; | |
146 | { | |
147 | hash_table_t new_htab; | |
148 | hash_table_entry_t *entry_ptr; | |
149 | hash_table_entry_t *new_entry_ptr; | |
150 | ||
151 | new_htab = create_hash_table (htab->number_of_elements * 2, | |
152 | htab->hash_function, htab->eq_function); | |
153 | for (entry_ptr = htab->entries; entry_ptr < htab->entries + htab->size; | |
154 | entry_ptr++) | |
155 | if (*entry_ptr != EMPTY_ENTRY && *entry_ptr != DELETED_ENTRY) | |
156 | { | |
157 | new_entry_ptr = find_hash_table_entry (new_htab, *entry_ptr, 1); | |
158 | *new_entry_ptr = (*entry_ptr); | |
159 | } | |
160 | free (htab->entries); | |
161 | *htab = (*new_htab); | |
162 | free (new_htab); | |
163 | } | |
164 | ||
165 | /* This function searches for hash table entry which contains element | |
166 | equal to given value or empty entry in which given value can be | |
167 | placed (if the element with given value does not exist in the | |
168 | table). The function works in two regimes. The first regime is | |
169 | used only for search. The second is used for search and | |
170 | reservation empty entry for given value. The table is expanded if | |
171 | occupancy (taking into accout also deleted elements) is more than | |
172 | 75%. Naturally the hash table must already exist. If reservation | |
173 | flag is TRUE then the element with given value should be inserted | |
174 | into the table entry before another call of | |
175 | `find_hash_table_entry'. */ | |
176 | ||
177 | hash_table_entry_t * | |
178 | find_hash_table_entry (htab, element, reserve) | |
179 | hash_table_t htab; | |
180 | hash_table_entry_t element; | |
181 | int reserve; | |
182 | { | |
183 | hash_table_entry_t *entry_ptr; | |
184 | hash_table_entry_t *first_deleted_entry_ptr; | |
185 | unsigned index, hash_value, secondary_hash_value; | |
186 | ||
187 | if (htab->size * 3 <= htab->number_of_elements * 4) | |
188 | { | |
189 | all_expansions++; | |
190 | expand_hash_table (htab); | |
191 | } | |
192 | hash_value = (*htab->hash_function) (element); | |
193 | secondary_hash_value = 1 + hash_value % (htab->size - 2); | |
194 | index = hash_value % htab->size; | |
195 | htab->searches++; | |
196 | all_searches++; | |
197 | first_deleted_entry_ptr = NULL; | |
198 | for (;;htab->collisions++, all_collisions++) | |
199 | { | |
200 | entry_ptr = htab->entries + index; | |
201 | if (*entry_ptr == EMPTY_ENTRY) | |
202 | { | |
203 | if (reserve) | |
204 | { | |
205 | htab->number_of_elements++; | |
206 | if (first_deleted_entry_ptr != NULL) | |
207 | { | |
208 | entry_ptr = first_deleted_entry_ptr; | |
209 | *entry_ptr = DELETED_ENTRY; | |
210 | } | |
211 | } | |
212 | break; | |
213 | } | |
214 | else if (*entry_ptr != DELETED_ENTRY) | |
215 | { | |
216 | if ((*htab->eq_function) (*entry_ptr, element)) | |
217 | break; | |
218 | } | |
219 | else if (first_deleted_entry_ptr == NULL) | |
220 | first_deleted_entry_ptr = entry_ptr; | |
221 | index += secondary_hash_value; | |
222 | if (index >= htab->size) | |
223 | index -= htab->size; | |
224 | } | |
225 | return entry_ptr; | |
226 | } | |
227 | ||
228 | /* This function deletes element with given value from hash table. | |
229 | The hash table entry value will be `DELETED_ENTRY' after the | |
230 | function call. Naturally the hash table must already exist. Hash | |
231 | table entry for given value should be not empty (or deleted). */ | |
232 | ||
233 | void | |
234 | remove_element_from_hash_table_entry (htab, element) | |
235 | hash_table_t htab; | |
236 | hash_table_entry_t element; | |
237 | { | |
238 | hash_table_entry_t *entry_ptr; | |
239 | ||
240 | entry_ptr = find_hash_table_entry (htab, element, 0); | |
241 | *entry_ptr = DELETED_ENTRY; | |
242 | htab->number_of_deleted_elements++; | |
243 | } | |
244 | ||
245 | /* The following function returns current size of given hash table. */ | |
246 | ||
247 | size_t | |
248 | hash_table_size (htab) | |
249 | hash_table_t htab; | |
250 | { | |
251 | return htab->size; | |
252 | } | |
253 | ||
254 | /* The following function returns current number of elements in given | |
255 | hash table. */ | |
256 | ||
257 | size_t | |
258 | hash_table_elements_number (htab) | |
259 | hash_table_t htab; | |
260 | { | |
261 | return htab->number_of_elements - htab->number_of_deleted_elements; | |
262 | } | |
263 | ||
264 | /* The following function returns number of percents of fixed | |
265 | collisions during all work with given hash table. */ | |
266 | ||
267 | int | |
268 | hash_table_collisions (htab) | |
269 | hash_table_t htab; | |
270 | { | |
271 | int searches; | |
272 | ||
273 | searches = htab->searches; | |
274 | if (searches == 0) | |
275 | searches++; | |
276 | return htab->collisions * 100 / searches; | |
277 | } | |
278 | ||
279 | /* The following function returns number of percents of fixed | |
280 | collisions during all work with all hash tables. */ | |
281 | ||
282 | int | |
283 | all_hash_table_collisions () | |
284 | { | |
285 | int searches; | |
286 | ||
287 | searches = all_searches; | |
288 | if (searches == 0) | |
289 | searches++; | |
290 | return all_collisions * 100 / searches; | |
291 | } |