1 /* hash - hashing table processing.
2 Copyright (C) 1998-1999, 2001, 2003, 2009-2023 Free Software Foundation,
3 Inc.
4 Written by Jim Meyering <meyering@ascend.com>, 1998.
5
6 This file is free software: you can redistribute it and/or modify
7 it under the terms of the GNU Lesser General Public License as
8 published by the Free Software Foundation; either version 2.1 of the
9 License, or (at your option) any later version.
10
11 This file 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 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public License
17 along with this program. If not, see <https://www.gnu.org/licenses/>. */
18
19 /* A generic hash table package. */
20
21 /* Make sure USE_OBSTACK is defined to 1 if you want the allocator to use
22 obstacks instead of malloc, and recompile 'hash.c' with same setting. */
23
24 #ifndef HASH_H_
25 # define HASH_H_
26
27 /* This file uses _GL_ATTRIBUTE_DEALLOC, _GL_ATTRIBUTE_DEPRECATED,
28 _GL_ATTRIBUTE_MALLOC, _GL_ATTRIBUTE_NODISCARD, _GL_ATTRIBUTE_PURE,
29 _GL_ATTRIBUTE_RETURNS_NONNULL. */
30 #if !_GL_CONFIG_H_INCLUDED
31 #error "Please include config.h first."
32 #endif
33
34 # include <stdio.h>
35
36 # ifdef __cplusplus
37 extern "C" {
38 # endif
39
40 struct hash_tuning
41 {
42 /* This structure is mainly used for 'hash_initialize', see the block
43 documentation of 'hash_reset_tuning' for more complete comments. */
44
45 float shrink_threshold; /* ratio of used buckets to trigger a shrink */
46 float shrink_factor; /* ratio of new smaller size to original size */
47 float growth_threshold; /* ratio of used buckets to trigger a growth */
48 float growth_factor; /* ratio of new bigger size to original size */
49 bool is_n_buckets; /* if CANDIDATE really means table size */
50 };
51
52 typedef struct hash_tuning Hash_tuning;
53
54 struct hash_table;
55
56 typedef struct hash_table Hash_table;
57
58 /*
59 * Information and lookup.
60 */
61
62 /* The following few functions provide information about the overall hash
63 table organization: the number of entries, number of buckets and maximum
64 length of buckets. */
65
66 /* Return the number of buckets in the hash table. The table size, the total
67 number of buckets (used plus unused), or the maximum number of slots, are
68 the same quantity. */
69 extern size_t hash_get_n_buckets (const Hash_table *table)
70 _GL_ATTRIBUTE_PURE;
71
72 /* Return the number of slots in use (non-empty buckets). */
73 extern size_t hash_get_n_buckets_used (const Hash_table *table)
74 _GL_ATTRIBUTE_PURE;
75
76 /* Return the number of active entries. */
77 extern size_t hash_get_n_entries (const Hash_table *table)
78 _GL_ATTRIBUTE_PURE;
79
80 /* Return the length of the longest chain (bucket). */
81 extern size_t hash_get_max_bucket_length (const Hash_table *table)
82 _GL_ATTRIBUTE_PURE;
83
84 /* Do a mild validation of a hash table, by traversing it and checking two
85 statistics. */
86 extern bool hash_table_ok (const Hash_table *table)
87 _GL_ATTRIBUTE_PURE;
88
89 extern void hash_print_statistics (const Hash_table *table, FILE *stream);
90
91 /* If ENTRY matches an entry already in the hash table, return the
92 entry from the table. Otherwise, return NULL. */
93 extern void *hash_lookup (const Hash_table *table, const void *entry);
94
95 /*
96 * Walking.
97 */
98
99 /* The functions in this page traverse the hash table and process the
100 contained entries. For the traversal to work properly, the hash table
101 should not be resized nor modified while any particular entry is being
102 processed. In particular, entries should not be added, and an entry
103 may be removed only if there is no shrink threshold and the entry being
104 removed has already been passed to hash_get_next. */
105
106 /* Return the first data in the table, or NULL if the table is empty. */
107 extern void *hash_get_first (const Hash_table *table)
108 _GL_ATTRIBUTE_PURE;
109
110 /* Return the user data for the entry following ENTRY, where ENTRY has been
111 returned by a previous call to either 'hash_get_first' or 'hash_get_next'.
112 Return NULL if there are no more entries. */
113 extern void *hash_get_next (const Hash_table *table, const void *entry);
114
115 /* Fill BUFFER with pointers to active user entries in the hash table, then
116 return the number of pointers copied. Do not copy more than BUFFER_SIZE
117 pointers. */
118 extern size_t hash_get_entries (const Hash_table *table, void **buffer,
119 size_t buffer_size);
120
121 typedef bool (*Hash_processor) (void *entry, void *processor_data);
122
123 /* Call a PROCESSOR function for each entry of a hash table, and return the
124 number of entries for which the processor function returned success. A
125 pointer to some PROCESSOR_DATA which will be made available to each call to
126 the processor function. The PROCESSOR accepts two arguments: the first is
127 the user entry being walked into, the second is the value of PROCESSOR_DATA
128 as received. The walking continue for as long as the PROCESSOR function
129 returns nonzero. When it returns zero, the walking is interrupted. */
130 extern size_t hash_do_for_each (const Hash_table *table,
131 Hash_processor processor, void *processor_data);
132
133 /*
134 * Allocation and clean-up.
135 */
136
137 /* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1.
138 This is a convenience routine for constructing other hashing functions. */
139 extern size_t hash_string (const char *string, size_t n_buckets)
140 _GL_ATTRIBUTE_PURE;
141
142 extern void hash_reset_tuning (Hash_tuning *tuning);
143
144 typedef size_t (*Hash_hasher) (const void *entry, size_t table_size);
145 typedef bool (*Hash_comparator) (const void *entry1, const void *entry2);
146 typedef void (*Hash_data_freer) (void *entry);
147
148 /* Reclaim all storage associated with a hash table. If a data_freer
149 function has been supplied by the user when the hash table was created,
150 this function applies it to the data of each entry before freeing that
151 entry. This function preserves errno, like 'free'. */
152 extern void hash_free (Hash_table *table);
153
154 /* Allocate and return a new hash table, or NULL upon failure. The initial
155 number of buckets is automatically selected so as to _guarantee_ that you
156 may insert at least CANDIDATE different user entries before any growth of
157 the hash table size occurs. So, if have a reasonably tight a-priori upper
158 bound on the number of entries you intend to insert in the hash table, you
159 may save some table memory and insertion time, by specifying it here. If
160 the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
161 argument has its meaning changed to the wanted number of buckets.
162
163 TUNING points to a structure of user-supplied values, in case some fine
164 tuning is wanted over the default behavior of the hasher. If TUNING is
165 NULL, the default tuning parameters are used instead. If TUNING is
166 provided but the values requested are out of bounds or might cause
167 rounding errors, return NULL.
168
169 The user-supplied HASHER function, when not NULL, accepts two
170 arguments ENTRY and TABLE_SIZE. It computes, by hashing ENTRY contents, a
171 slot number for that entry which should be in the range 0..TABLE_SIZE-1.
172 This slot number is then returned.
173
174 The user-supplied COMPARATOR function, when not NULL, accepts two
175 arguments pointing to user data, it then returns true for a pair of entries
176 that compare equal, or false otherwise. This function is internally called
177 on entries which are already known to hash to the same bucket index,
178 but which are distinct pointers.
179
180 The user-supplied DATA_FREER function, when not NULL, may be later called
181 with the user data as an argument, just before the entry containing the
182 data gets freed. This happens from within 'hash_free' or 'hash_clear'.
183 You should specify this function only if you want these functions to free
184 all of your 'data' data. This is typically the case when your data is
185 simply an auxiliary struct that you have malloc'd to aggregate several
186 values.
187
188 Set errno on failure; otherwise errno is unspecified. */
189 _GL_ATTRIBUTE_NODISCARD
190 extern Hash_table *hash_initialize (size_t candidate,
191 const Hash_tuning *tuning,
192 Hash_hasher hasher,
193 Hash_comparator comparator,
194 Hash_data_freer data_freer)
195 _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC (hash_free, 1);
196
197 /* Like hash_initialize, but invokes xalloc_die instead of returning NULL. */
198 /* This function is defined by module 'xhash'. */
199 _GL_ATTRIBUTE_NODISCARD
200 extern Hash_table *hash_xinitialize (size_t candidate,
201 const Hash_tuning *tuning,
202 Hash_hasher hasher,
203 Hash_comparator comparator,
204 Hash_data_freer data_freer)
205 _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC (hash_free, 1)
206 _GL_ATTRIBUTE_RETURNS_NONNULL;
207
208 /* Make all buckets empty, placing any chained entries on the free list.
209 Apply the user-specified function data_freer (if any) to the data of any
210 affected entries. */
211 extern void hash_clear (Hash_table *table);
212
213 /*
214 * Insertion and deletion.
215 */
216
217 /* For an already existing hash table, change the number of buckets through
218 specifying CANDIDATE. The contents of the hash table are preserved. The
219 new number of buckets is automatically selected so as to _guarantee_ that
220 the table may receive at least CANDIDATE different user entries, including
221 those already in the table, before any other growth of the hash table size
222 occurs. If TUNING->IS_N_BUCKETS is true, then CANDIDATE specifies the
223 exact number of buckets desired. Return true iff the rehash succeeded,
224 false (setting errno) otherwise. */
225 _GL_ATTRIBUTE_NODISCARD
226 extern bool hash_rehash (Hash_table *table, size_t candidate);
227
228 /* If ENTRY matches an entry already in the hash table, return the pointer
229 to the entry from the table. Otherwise, insert ENTRY and return ENTRY.
230 Return NULL (setting errno) if the storage required for insertion
231 cannot be allocated. This implementation does not support
232 duplicate entries or insertion of NULL. */
233 _GL_ATTRIBUTE_NODISCARD
234 extern void *hash_insert (Hash_table *table, const void *entry);
235
236 /* Same as hash_insert, but invokes xalloc_die instead of returning NULL. */
237 /* This function is defined by module 'xhash'. */
238 extern void *hash_xinsert (Hash_table *table, const void *entry);
239
240 /* Insert ENTRY into hash TABLE if there is not already a matching entry.
241
242 Return -1 (setting errno) upon memory allocation failure.
243 Return 1 if insertion succeeded.
244 Return 0 if there is already a matching entry in the table,
245 and in that case, if MATCHED_ENT is non-NULL, set *MATCHED_ENT
246 to that entry.
247
248 This interface is easier to use than hash_insert when you must
249 distinguish between the latter two cases. More importantly,
250 hash_insert is unusable for some types of ENTRY values. When using
251 hash_insert, the only way to distinguish those cases is to compare
252 the return value and ENTRY. That works only when you can have two
253 different ENTRY values that point to data that compares "equal". Thus,
254 when the ENTRY value is a simple scalar, you must use
255 hash_insert_if_absent. ENTRY must not be NULL. */
256 extern int hash_insert_if_absent (Hash_table *table, const void *entry,
257 const void **matched_ent);
258
259 /* If ENTRY is already in the table, remove it and return the just-deleted
260 data (the user may want to deallocate its storage). If ENTRY is not in the
261 table, don't modify the table and return NULL. */
262 extern void *hash_remove (Hash_table *table, const void *entry);
263
264 /* Same as hash_remove. This interface is deprecated.
265 FIXME: Remove in 2022. */
266 _GL_ATTRIBUTE_DEPRECATED
267 extern void *hash_delete (Hash_table *table, const void *entry);
268
269 # ifdef __cplusplus
270 }
271 # endif
272
273 #endif