1 /* hash - hashing table processing.
2 Copyright (C) 1998-1999, 2001, 2003, 2009-2021 Free Software Foundation,
3 Inc.
4 Written by Jim Meyering <meyering@ascend.com>, 1998.
5
6 This program 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 of the License, or
9 (at your option) any later version.
10
11 This program 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 You should have received a copy of the GNU 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 # include <stdio.h>
28 # include <stdbool.h>
29
30 # ifdef __cplusplus
31 extern "C" {
32 # endif
33
34 struct hash_tuning
35 {
36 /* This structure is mainly used for 'hash_initialize', see the block
37 documentation of 'hash_reset_tuning' for more complete comments. */
38
39 float shrink_threshold; /* ratio of used buckets to trigger a shrink */
40 float shrink_factor; /* ratio of new smaller size to original size */
41 float growth_threshold; /* ratio of used buckets to trigger a growth */
42 float growth_factor; /* ratio of new bigger size to original size */
43 bool is_n_buckets; /* if CANDIDATE really means table size */
44 };
45
46 typedef struct hash_tuning Hash_tuning;
47
48 struct hash_table;
49
50 typedef struct hash_table Hash_table;
51
52 /*
53 * Information and lookup.
54 */
55
56 /* The following few functions provide information about the overall hash
57 table organization: the number of entries, number of buckets and maximum
58 length of buckets. */
59
60 /* Return the number of buckets in the hash table. The table size, the total
61 number of buckets (used plus unused), or the maximum number of slots, are
62 the same quantity. */
63 extern size_t hash_get_n_buckets (const Hash_table *table)
64 _GL_ATTRIBUTE_PURE;
65
66 /* Return the number of slots in use (non-empty buckets). */
67 extern size_t hash_get_n_buckets_used (const Hash_table *table)
68 _GL_ATTRIBUTE_PURE;
69
70 /* Return the number of active entries. */
71 extern size_t hash_get_n_entries (const Hash_table *table)
72 _GL_ATTRIBUTE_PURE;
73
74 /* Return the length of the longest chain (bucket). */
75 extern size_t hash_get_max_bucket_length (const Hash_table *table)
76 _GL_ATTRIBUTE_PURE;
77
78 /* Do a mild validation of a hash table, by traversing it and checking two
79 statistics. */
80 extern bool hash_table_ok (const Hash_table *table)
81 _GL_ATTRIBUTE_PURE;
82
83 extern void hash_print_statistics (const Hash_table *table, FILE *stream);
84
85 /* If ENTRY matches an entry already in the hash table, return the
86 entry from the table. Otherwise, return NULL. */
87 extern void *hash_lookup (const Hash_table *table, const void *entry);
88
89 /*
90 * Walking.
91 */
92
93 /* The functions in this page traverse the hash table and process the
94 contained entries. For the traversal to work properly, the hash table
95 should not be resized nor modified while any particular entry is being
96 processed. In particular, entries should not be added, and an entry
97 may be removed only if there is no shrink threshold and the entry being
98 removed has already been passed to hash_get_next. */
99
100 /* Return the first data in the table, or NULL if the table is empty. */
101 extern void *hash_get_first (const Hash_table *table)
102 _GL_ATTRIBUTE_PURE;
103
104 /* Return the user data for the entry following ENTRY, where ENTRY has been
105 returned by a previous call to either 'hash_get_first' or 'hash_get_next'.
106 Return NULL if there are no more entries. */
107 extern void *hash_get_next (const Hash_table *table, const void *entry);
108
109 /* Fill BUFFER with pointers to active user entries in the hash table, then
110 return the number of pointers copied. Do not copy more than BUFFER_SIZE
111 pointers. */
112 extern size_t hash_get_entries (const Hash_table *table, void **buffer,
113 size_t buffer_size);
114
115 typedef bool (*Hash_processor) (void *entry, void *processor_data);
116
117 /* Call a PROCESSOR function for each entry of a hash table, and return the
118 number of entries for which the processor function returned success. A
119 pointer to some PROCESSOR_DATA which will be made available to each call to
120 the processor function. The PROCESSOR accepts two arguments: the first is
121 the user entry being walked into, the second is the value of PROCESSOR_DATA
122 as received. The walking continue for as long as the PROCESSOR function
123 returns nonzero. When it returns zero, the walking is interrupted. */
124 extern size_t hash_do_for_each (const Hash_table *table,
125 Hash_processor processor, void *processor_data);
126
127 /*
128 * Allocation and clean-up.
129 */
130
131 /* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1.
132 This is a convenience routine for constructing other hashing functions. */
133 extern size_t hash_string (const char *string, size_t n_buckets)
134 _GL_ATTRIBUTE_PURE;
135
136 extern void hash_reset_tuning (Hash_tuning *tuning);
137
138 typedef size_t (*Hash_hasher) (const void *entry, size_t table_size);
139 typedef bool (*Hash_comparator) (const void *entry1, const void *entry2);
140 typedef void (*Hash_data_freer) (void *entry);
141
142 /* Allocate and return a new hash table, or NULL upon failure. The initial
143 number of buckets is automatically selected so as to _guarantee_ that you
144 may insert at least CANDIDATE different user entries before any growth of
145 the hash table size occurs. So, if have a reasonably tight a-priori upper
146 bound on the number of entries you intend to insert in the hash table, you
147 may save some table memory and insertion time, by specifying it here. If
148 the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
149 argument has its meaning changed to the wanted number of buckets.
150
151 TUNING points to a structure of user-supplied values, in case some fine
152 tuning is wanted over the default behavior of the hasher. If TUNING is
153 NULL, the default tuning parameters are used instead. If TUNING is
154 provided but the values requested are out of bounds or might cause
155 rounding errors, return NULL.
156
157 The user-supplied HASHER function, when not NULL, accepts two
158 arguments ENTRY and TABLE_SIZE. It computes, by hashing ENTRY contents, a
159 slot number for that entry which should be in the range 0..TABLE_SIZE-1.
160 This slot number is then returned.
161
162 The user-supplied COMPARATOR function, when not NULL, accepts two
163 arguments pointing to user data, it then returns true for a pair of entries
164 that compare equal, or false otherwise. This function is internally called
165 on entries which are already known to hash to the same bucket index,
166 but which are distinct pointers.
167
168 The user-supplied DATA_FREER function, when not NULL, may be later called
169 with the user data as an argument, just before the entry containing the
170 data gets freed. This happens from within 'hash_free' or 'hash_clear'.
171 You should specify this function only if you want these functions to free
172 all of your 'data' data. This is typically the case when your data is
173 simply an auxiliary struct that you have malloc'd to aggregate several
174 values. */
175 extern Hash_table *hash_initialize (size_t candidate,
176 const Hash_tuning *tuning,
177 Hash_hasher hasher,
178 Hash_comparator comparator,
179 Hash_data_freer data_freer)
180 _GL_ATTRIBUTE_NODISCARD;
181
182 /* Same as hash_initialize, but invokes xalloc_die on memory exhaustion. */
183 /* This function is defined by module 'xhash'. */
184 extern Hash_table *hash_xinitialize (size_t candidate,
185 const Hash_tuning *tuning,
186 Hash_hasher hasher,
187 Hash_comparator comparator,
188 Hash_data_freer data_freer)
189 _GL_ATTRIBUTE_NODISCARD;
190
191 /* Make all buckets empty, placing any chained entries on the free list.
192 Apply the user-specified function data_freer (if any) to the datas of any
193 affected entries. */
194 extern void hash_clear (Hash_table *table);
195
196 /* Reclaim all storage associated with a hash table. If a data_freer
197 function has been supplied by the user when the hash table was created,
198 this function applies it to the data of each entry before freeing that
199 entry. */
200 extern void hash_free (Hash_table *table);
201
202 /*
203 * Insertion and deletion.
204 */
205
206 /* For an already existing hash table, change the number of buckets through
207 specifying CANDIDATE. The contents of the hash table are preserved. The
208 new number of buckets is automatically selected so as to _guarantee_ that
209 the table may receive at least CANDIDATE different user entries, including
210 those already in the table, before any other growth of the hash table size
211 occurs. If TUNING->IS_N_BUCKETS is true, then CANDIDATE specifies the
212 exact number of buckets desired. Return true iff the rehash succeeded. */
213 extern bool hash_rehash (Hash_table *table, size_t candidate)
214 _GL_ATTRIBUTE_NODISCARD;
215
216 /* If ENTRY matches an entry already in the hash table, return the pointer
217 to the entry from the table. Otherwise, insert ENTRY and return ENTRY.
218 Return NULL if the storage required for insertion cannot be allocated.
219 This implementation does not support duplicate entries or insertion of
220 NULL. */
221 extern void *hash_insert (Hash_table *table, const void *entry)
222 _GL_ATTRIBUTE_NODISCARD;
223
224 /* Same as hash_insert, but invokes xalloc_die on memory exhaustion. */
225 /* This function is defined by module 'xhash'. */
226 extern void *hash_xinsert (Hash_table *table, const void *entry);
227
228 /* Insert ENTRY into hash TABLE if there is not already a matching entry.
229
230 Return -1 upon memory allocation failure.
231 Return 1 if insertion succeeded.
232 Return 0 if there is already a matching entry in the table,
233 and in that case, if MATCHED_ENT is non-NULL, set *MATCHED_ENT
234 to that entry.
235
236 This interface is easier to use than hash_insert when you must
237 distinguish between the latter two cases. More importantly,
238 hash_insert is unusable for some types of ENTRY values. When using
239 hash_insert, the only way to distinguish those cases is to compare
240 the return value and ENTRY. That works only when you can have two
241 different ENTRY values that point to data that compares "equal". Thus,
242 when the ENTRY value is a simple scalar, you must use
243 hash_insert_if_absent. ENTRY must not be NULL. */
244 extern int hash_insert_if_absent (Hash_table *table, const void *entry,
245 const void **matched_ent);
246
247 /* If ENTRY is already in the table, remove it and return the just-deleted
248 data (the user may want to deallocate its storage). If ENTRY is not in the
249 table, don't modify the table and return NULL. */
250 extern void *hash_remove (Hash_table *table, const void *entry);
251
252 /* Same as hash_remove. This interface is deprecated.
253 FIXME: Remove in 2022. */
254 extern void *hash_delete (Hash_table *table, const void *entry)
255 _GL_ATTRIBUTE_DEPRECATED;
256
257 # ifdef __cplusplus
258 }
259 # endif
260
261 #endif