1 /* hash - hashing table processing.
3 Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007,
4 2009 Free Software Foundation, Inc.
6 Written by Jim Meyering, 1992.
8 This program is free software: you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or
11 (at your option) any later version.
13 This program is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with this program. If not, see <http://www.gnu.org/licenses/>. */
21 /* A generic hash table package. */
23 /* Define USE_OBSTACK to 1 if you want the allocator to use obstacks instead
24 of malloc. If you change USE_OBSTACK, you have to recompile! */
30 #include "bitrotate.h"
39 # ifndef obstack_chunk_alloc
40 # define obstack_chunk_alloc malloc
42 # ifndef obstack_chunk_free
43 # define obstack_chunk_free free
50 struct hash_entry *next;
55 /* The array of buckets starts at BUCKET and extends to BUCKET_LIMIT-1,
56 for a possibility of N_BUCKETS. Among those, N_BUCKETS_USED buckets
57 are not empty, there are N_ENTRIES active entries in the table. */
58 struct hash_entry *bucket;
59 struct hash_entry const *bucket_limit;
61 size_t n_buckets_used;
64 /* Tuning arguments, kept in a physically separate structure. */
65 const Hash_tuning *tuning;
67 /* Three functions are given to `hash_initialize', see the documentation
68 block for this function. In a word, HASHER randomizes a user entry
69 into a number up from 0 up to some maximum minus 1; COMPARATOR returns
70 true if two user entries compare equally; and DATA_FREER is the cleanup
71 function for a user entry. */
73 Hash_comparator comparator;
74 Hash_data_freer data_freer;
76 /* A linked list of freed struct hash_entry structs. */
77 struct hash_entry *free_entry_list;
80 /* Whenever obstacks are used, it is possible to allocate all overflowed
81 entries into a single stack, so they all can be freed in a single
82 operation. It is not clear if the speedup is worth the trouble. */
83 struct obstack entry_stack;
87 /* A hash table contains many internal entries, each holding a pointer to
88 some user-provided data (also called a user entry). An entry indistinctly
89 refers to both the internal entry and its associated user entry. A user
90 entry contents may be hashed by a randomization function (the hashing
91 function, or just `hasher' for short) into a number (or `slot') between 0
92 and the current table size. At each slot position in the hash table,
93 starts a linked chain of entries for which the user data all hash to this
94 slot. A bucket is the collection of all entries hashing to the same slot.
96 A good `hasher' function will distribute entries rather evenly in buckets.
97 In the ideal case, the length of each bucket is roughly the number of
98 entries divided by the table size. Finding the slot for a data is usually
99 done in constant time by the `hasher', and the later finding of a precise
100 entry is linear in time with the size of the bucket. Consequently, a
101 larger hash table size (that is, a larger number of buckets) is prone to
102 yielding shorter chains, *given* the `hasher' function behaves properly.
104 Long buckets slow down the lookup algorithm. One might use big hash table
105 sizes in hope to reduce the average length of buckets, but this might
106 become inordinate, as unused slots in the hash table take some space. The
107 best bet is to make sure you are using a good `hasher' function (beware
108 that those are not that easy to write! :-), and to use a table size
109 larger than the actual number of entries. */
111 /* If an insertion makes the ratio of nonempty buckets to table size larger
112 than the growth threshold (a number between 0.0 and 1.0), then increase
113 the table size by multiplying by the growth factor (a number greater than
114 1.0). The growth threshold defaults to 0.8, and the growth factor
115 defaults to 1.414, meaning that the table will have doubled its size
116 every second time 80% of the buckets get used. */
117 #define DEFAULT_GROWTH_THRESHOLD 0.8
118 #define DEFAULT_GROWTH_FACTOR 1.414
120 /* If a deletion empties a bucket and causes the ratio of used buckets to
121 table size to become smaller than the shrink threshold (a number between
122 0.0 and 1.0), then shrink the table by multiplying by the shrink factor (a
123 number greater than the shrink threshold but smaller than 1.0). The shrink
124 threshold and factor default to 0.0 and 1.0, meaning that the table never
126 #define DEFAULT_SHRINK_THRESHOLD 0.0
127 #define DEFAULT_SHRINK_FACTOR 1.0
129 /* Use this to initialize or reset a TUNING structure to
130 some sensible values. */
131 static const Hash_tuning default_tuning =
133 DEFAULT_SHRINK_THRESHOLD,
134 DEFAULT_SHRINK_FACTOR,
135 DEFAULT_GROWTH_THRESHOLD,
136 DEFAULT_GROWTH_FACTOR,
140 /* Information and lookup. */
142 /* The following few functions provide information about the overall hash
143 table organization: the number of entries, number of buckets and maximum
144 length of buckets. */
146 /* Return the number of buckets in the hash table. The table size, the total
147 number of buckets (used plus unused), or the maximum number of slots, are
148 the same quantity. */
151 hash_get_n_buckets (const Hash_table *table)
153 return table->n_buckets;
156 /* Return the number of slots in use (non-empty buckets). */
159 hash_get_n_buckets_used (const Hash_table *table)
161 return table->n_buckets_used;
164 /* Return the number of active entries. */
167 hash_get_n_entries (const Hash_table *table)
169 return table->n_entries;
172 /* Return the length of the longest chain (bucket). */
175 hash_get_max_bucket_length (const Hash_table *table)
177 struct hash_entry const *bucket;
178 size_t max_bucket_length = 0;
180 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
184 struct hash_entry const *cursor = bucket;
185 size_t bucket_length = 1;
187 while (cursor = cursor->next, cursor)
190 if (bucket_length > max_bucket_length)
191 max_bucket_length = bucket_length;
195 return max_bucket_length;
198 /* Do a mild validation of a hash table, by traversing it and checking two
202 hash_table_ok (const Hash_table *table)
204 struct hash_entry const *bucket;
205 size_t n_buckets_used = 0;
206 size_t n_entries = 0;
208 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
212 struct hash_entry const *cursor = bucket;
214 /* Count bucket head. */
218 /* Count bucket overflow. */
219 while (cursor = cursor->next, cursor)
224 if (n_buckets_used == table->n_buckets_used && n_entries == table->n_entries)
231 hash_print_statistics (const Hash_table *table, FILE *stream)
233 size_t n_entries = hash_get_n_entries (table);
234 size_t n_buckets = hash_get_n_buckets (table);
235 size_t n_buckets_used = hash_get_n_buckets_used (table);
236 size_t max_bucket_length = hash_get_max_bucket_length (table);
238 fprintf (stream, "# entries: %lu\n", (unsigned long int) n_entries);
239 fprintf (stream, "# buckets: %lu\n", (unsigned long int) n_buckets);
240 fprintf (stream, "# buckets used: %lu (%.2f%%)\n",
241 (unsigned long int) n_buckets_used,
242 (100.0 * n_buckets_used) / n_buckets);
243 fprintf (stream, "max bucket length: %lu\n",
244 (unsigned long int) max_bucket_length);
247 /* If ENTRY matches an entry already in the hash table, return the
248 entry from the table. Otherwise, return NULL. */
251 hash_lookup (const Hash_table *table, const void *entry)
253 struct hash_entry const *bucket
254 = table->bucket + table->hasher (entry, table->n_buckets);
255 struct hash_entry const *cursor;
257 if (! (bucket < table->bucket_limit))
260 if (bucket->data == NULL)
263 for (cursor = bucket; cursor; cursor = cursor->next)
264 if (entry == cursor->data || table->comparator (entry, cursor->data))
272 /* The functions in this page traverse the hash table and process the
273 contained entries. For the traversal to work properly, the hash table
274 should not be resized nor modified while any particular entry is being
275 processed. In particular, entries should not be added, and an entry
276 may be removed only if there is no shrink threshold and the entry being
277 removed has already been passed to hash_get_next. */
279 /* Return the first data in the table, or NULL if the table is empty. */
282 hash_get_first (const Hash_table *table)
284 struct hash_entry const *bucket;
286 if (table->n_entries == 0)
289 for (bucket = table->bucket; ; bucket++)
290 if (! (bucket < table->bucket_limit))
292 else if (bucket->data)
296 /* Return the user data for the entry following ENTRY, where ENTRY has been
297 returned by a previous call to either `hash_get_first' or `hash_get_next'.
298 Return NULL if there are no more entries. */
301 hash_get_next (const Hash_table *table, const void *entry)
303 struct hash_entry const *bucket
304 = table->bucket + table->hasher (entry, table->n_buckets);
305 struct hash_entry const *cursor;
307 if (! (bucket < table->bucket_limit))
310 /* Find next entry in the same bucket. */
311 for (cursor = bucket; cursor; cursor = cursor->next)
312 if (cursor->data == entry && cursor->next)
313 return cursor->next->data;
315 /* Find first entry in any subsequent bucket. */
316 while (++bucket < table->bucket_limit)
324 /* Fill BUFFER with pointers to active user entries in the hash table, then
325 return the number of pointers copied. Do not copy more than BUFFER_SIZE
329 hash_get_entries (const Hash_table *table, void **buffer,
333 struct hash_entry const *bucket;
334 struct hash_entry const *cursor;
336 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
340 for (cursor = bucket; cursor; cursor = cursor->next)
342 if (counter >= buffer_size)
344 buffer[counter++] = cursor->data;
352 /* Call a PROCESSOR function for each entry of a hash table, and return the
353 number of entries for which the processor function returned success. A
354 pointer to some PROCESSOR_DATA which will be made available to each call to
355 the processor function. The PROCESSOR accepts two arguments: the first is
356 the user entry being walked into, the second is the value of PROCESSOR_DATA
357 as received. The walking continue for as long as the PROCESSOR function
358 returns nonzero. When it returns zero, the walking is interrupted. */
361 hash_do_for_each (const Hash_table *table, Hash_processor processor,
362 void *processor_data)
365 struct hash_entry const *bucket;
366 struct hash_entry const *cursor;
368 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
372 for (cursor = bucket; cursor; cursor = cursor->next)
374 if (! processor (cursor->data, processor_data))
384 /* Allocation and clean-up. */
386 /* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1.
387 This is a convenience routine for constructing other hashing functions. */
391 /* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see
392 B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,
393 Software--practice & experience 20, 2 (Feb 1990), 209-224. Good hash
394 algorithms tend to be domain-specific, so what's good for [diffutils'] io.c
395 may not be good for your application." */
398 hash_string (const char *string, size_t n_buckets)
400 # define HASH_ONE_CHAR(Value, Byte) \
401 ((Byte) + rotl_sz (Value, 7))
406 for (; (ch = *string); string++)
407 value = HASH_ONE_CHAR (value, ch);
408 return value % n_buckets;
410 # undef HASH_ONE_CHAR
413 #else /* not USE_DIFF_HASH */
415 /* This one comes from `recode', and performs a bit better than the above as
416 per a few experiments. It is inspired from a hashing routine found in the
417 very old Cyber `snoop', itself written in typical Greg Mansfield style.
418 (By the way, what happened to this excellent man? Is he still alive?) */
421 hash_string (const char *string, size_t n_buckets)
426 for (; (ch = *string); string++)
427 value = (value * 31 + ch) % n_buckets;
431 #endif /* not USE_DIFF_HASH */
433 /* Return true if CANDIDATE is a prime number. CANDIDATE should be an odd
434 number at least equal to 11. */
437 is_prime (size_t candidate)
440 size_t square = divisor * divisor;
442 while (square < candidate && (candidate % divisor))
445 square += 4 * divisor;
449 return (candidate % divisor ? true : false);
452 /* Round a given CANDIDATE number up to the nearest prime, and return that
453 prime. Primes lower than 10 are merely skipped. */
456 next_prime (size_t candidate)
458 /* Skip small primes. */
462 /* Make it definitely odd. */
465 while (!is_prime (candidate))
472 hash_reset_tuning (Hash_tuning *tuning)
474 *tuning = default_tuning;
477 /* If the user passes a NULL hasher, we hash the raw pointer. */
479 raw_hasher (const void *data, size_t n)
481 /* When hashing unique pointers, it is often the case that they were
482 generated by malloc and thus have the property that the low-order
483 bits are 0. As this tends to give poorer performance with small
484 tables, we rotate the pointer value before performing division,
485 in an attempt to improve hash quality. */
486 size_t val = rotr_sz ((size_t) data, 3);
490 /* If the user passes a NULL comparator, we use pointer comparison. */
492 raw_comparator (const void *a, const void *b)
498 /* For the given hash TABLE, check the user supplied tuning structure for
499 reasonable values, and return true if there is no gross error with it.
500 Otherwise, definitively reset the TUNING field to some acceptable default
501 in the hash table (that is, the user loses the right of further modifying
502 tuning arguments), and return false. */
505 check_tuning (Hash_table *table)
507 const Hash_tuning *tuning = table->tuning;
508 if (tuning == &default_tuning)
511 /* Be a bit stricter than mathematics would require, so that
512 rounding errors in size calculations do not cause allocations to
513 fail to grow or shrink as they should. The smallest allocation
514 is 11 (due to next_prime's algorithm), so an epsilon of 0.1
515 should be good enough. */
516 float epsilon = 0.1f;
518 if (epsilon < tuning->growth_threshold
519 && tuning->growth_threshold < 1 - epsilon
520 && 1 + epsilon < tuning->growth_factor
521 && 0 <= tuning->shrink_threshold
522 && tuning->shrink_threshold + epsilon < tuning->shrink_factor
523 && tuning->shrink_factor <= 1
524 && tuning->shrink_threshold + epsilon < tuning->growth_threshold)
527 table->tuning = &default_tuning;
531 /* Allocate and return a new hash table, or NULL upon failure. The initial
532 number of buckets is automatically selected so as to _guarantee_ that you
533 may insert at least CANDIDATE different user entries before any growth of
534 the hash table size occurs. So, if have a reasonably tight a-priori upper
535 bound on the number of entries you intend to insert in the hash table, you
536 may save some table memory and insertion time, by specifying it here. If
537 the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
538 argument has its meaning changed to the wanted number of buckets.
540 TUNING points to a structure of user-supplied values, in case some fine
541 tuning is wanted over the default behavior of the hasher. If TUNING is
542 NULL, the default tuning parameters are used instead. If TUNING is
543 provided but the values requested are out of bounds or might cause
544 rounding errors, return NULL.
546 The user-supplied HASHER function, when not NULL, accepts two
547 arguments ENTRY and TABLE_SIZE. It computes, by hashing ENTRY contents, a
548 slot number for that entry which should be in the range 0..TABLE_SIZE-1.
549 This slot number is then returned.
551 The user-supplied COMPARATOR function, when not NULL, accepts two
552 arguments pointing to user data, it then returns true for a pair of entries
553 that compare equal, or false otherwise. This function is internally called
554 on entries which are already known to hash to the same bucket index,
555 but which are distinct pointers.
557 The user-supplied DATA_FREER function, when not NULL, may be later called
558 with the user data as an argument, just before the entry containing the
559 data gets freed. This happens from within `hash_free' or `hash_clear'.
560 You should specify this function only if you want these functions to free
561 all of your `data' data. This is typically the case when your data is
562 simply an auxiliary struct that you have malloc'd to aggregate several
566 hash_initialize (size_t candidate, const Hash_tuning *tuning,
567 Hash_hasher hasher, Hash_comparator comparator,
568 Hash_data_freer data_freer)
574 if (comparator == NULL)
575 comparator = raw_comparator;
577 table = malloc (sizeof *table);
582 tuning = &default_tuning;
583 table->tuning = tuning;
584 if (!check_tuning (table))
586 /* Fail if the tuning options are invalid. This is the only occasion
587 when the user gets some feedback about it. Once the table is created,
588 if the user provides invalid tuning options, we silently revert to
589 using the defaults, and ignore further request to change the tuning
594 if (!tuning->is_n_buckets)
596 float new_candidate = candidate / tuning->growth_threshold;
597 if (SIZE_MAX <= new_candidate)
599 candidate = new_candidate;
602 if (xalloc_oversized (candidate, sizeof *table->bucket))
604 table->n_buckets = next_prime (candidate);
605 if (xalloc_oversized (table->n_buckets, sizeof *table->bucket))
608 table->bucket = calloc (table->n_buckets, sizeof *table->bucket);
609 if (table->bucket == NULL)
611 table->bucket_limit = table->bucket + table->n_buckets;
612 table->n_buckets_used = 0;
613 table->n_entries = 0;
615 table->hasher = hasher;
616 table->comparator = comparator;
617 table->data_freer = data_freer;
619 table->free_entry_list = NULL;
621 obstack_init (&table->entry_stack);
630 /* Make all buckets empty, placing any chained entries on the free list.
631 Apply the user-specified function data_freer (if any) to the datas of any
635 hash_clear (Hash_table *table)
637 struct hash_entry *bucket;
639 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
643 struct hash_entry *cursor;
644 struct hash_entry *next;
646 /* Free the bucket overflow. */
647 for (cursor = bucket->next; cursor; cursor = next)
649 if (table->data_freer)
650 table->data_freer (cursor->data);
654 /* Relinking is done one entry at a time, as it is to be expected
655 that overflows are either rare or short. */
656 cursor->next = table->free_entry_list;
657 table->free_entry_list = cursor;
660 /* Free the bucket head. */
661 if (table->data_freer)
662 table->data_freer (bucket->data);
668 table->n_buckets_used = 0;
669 table->n_entries = 0;
672 /* Reclaim all storage associated with a hash table. If a data_freer
673 function has been supplied by the user when the hash table was created,
674 this function applies it to the data of each entry before freeing that
678 hash_free (Hash_table *table)
680 struct hash_entry *bucket;
681 struct hash_entry *cursor;
682 struct hash_entry *next;
684 /* Call the user data_freer function. */
685 if (table->data_freer && table->n_entries)
687 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
691 for (cursor = bucket; cursor; cursor = cursor->next)
692 table->data_freer (cursor->data);
699 obstack_free (&table->entry_stack, NULL);
703 /* Free all bucket overflowed entries. */
704 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
706 for (cursor = bucket->next; cursor; cursor = next)
713 /* Also reclaim the internal list of previously freed entries. */
714 for (cursor = table->free_entry_list; cursor; cursor = next)
722 /* Free the remainder of the hash table structure. */
723 free (table->bucket);
727 /* Insertion and deletion. */
729 /* Get a new hash entry for a bucket overflow, possibly by recycling a
730 previously freed one. If this is not possible, allocate a new one. */
732 static struct hash_entry *
733 allocate_entry (Hash_table *table)
735 struct hash_entry *new;
737 if (table->free_entry_list)
739 new = table->free_entry_list;
740 table->free_entry_list = new->next;
745 new = obstack_alloc (&table->entry_stack, sizeof *new);
747 new = malloc (sizeof *new);
754 /* Free a hash entry which was part of some bucket overflow,
755 saving it for later recycling. */
758 free_entry (Hash_table *table, struct hash_entry *entry)
761 entry->next = table->free_entry_list;
762 table->free_entry_list = entry;
765 /* This private function is used to help with insertion and deletion. When
766 ENTRY matches an entry in the table, return a pointer to the corresponding
767 user data and set *BUCKET_HEAD to the head of the selected bucket.
768 Otherwise, return NULL. When DELETE is true and ENTRY matches an entry in
769 the table, unlink the matching entry. */
772 hash_find_entry (Hash_table *table, const void *entry,
773 struct hash_entry **bucket_head, bool delete)
775 struct hash_entry *bucket
776 = table->bucket + table->hasher (entry, table->n_buckets);
777 struct hash_entry *cursor;
779 if (! (bucket < table->bucket_limit))
782 *bucket_head = bucket;
784 /* Test for empty bucket. */
785 if (bucket->data == NULL)
788 /* See if the entry is the first in the bucket. */
789 if (entry == bucket->data || table->comparator (entry, bucket->data))
791 void *data = bucket->data;
797 struct hash_entry *next = bucket->next;
799 /* Bump the first overflow entry into the bucket head, then save
800 the previous first overflow entry for later recycling. */
802 free_entry (table, next);
813 /* Scan the bucket overflow. */
814 for (cursor = bucket; cursor->next; cursor = cursor->next)
816 if (entry == cursor->next->data
817 || table->comparator (entry, cursor->next->data))
819 void *data = cursor->next->data;
823 struct hash_entry *next = cursor->next;
825 /* Unlink the entry to delete, then save the freed entry for later
827 cursor->next = next->next;
828 free_entry (table, next);
835 /* No entry found. */
839 /* For an already existing hash table, change the number of buckets through
840 specifying CANDIDATE. The contents of the hash table are preserved. The
841 new number of buckets is automatically selected so as to _guarantee_ that
842 the table may receive at least CANDIDATE different user entries, including
843 those already in the table, before any other growth of the hash table size
844 occurs. If TUNING->IS_N_BUCKETS is true, then CANDIDATE specifies the
845 exact number of buckets desired. Return true iff the rehash succeeded. */
848 hash_rehash (Hash_table *table, size_t candidate)
850 Hash_table *new_table;
851 struct hash_entry *bucket;
852 struct hash_entry *cursor;
853 struct hash_entry *next;
855 new_table = hash_initialize (candidate, table->tuning, table->hasher,
856 table->comparator, table->data_freer);
857 if (new_table == NULL)
859 if (new_table->n_buckets == table->n_buckets)
861 free (new_table->bucket);
866 /* Merely reuse the extra old space into the new table. */
868 obstack_free (&new_table->entry_stack, NULL);
869 new_table->entry_stack = table->entry_stack;
871 new_table->free_entry_list = table->free_entry_list;
873 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
875 for (cursor = bucket; cursor; cursor = next)
877 void *data = cursor->data;
878 struct hash_entry *new_bucket
880 + new_table->hasher (data, new_table->n_buckets));
882 if (! (new_bucket < new_table->bucket_limit))
887 if (new_bucket->data)
889 if (cursor == bucket)
891 /* Allocate or recycle an entry, when moving from a bucket
892 header into a bucket overflow. */
893 struct hash_entry *new_entry = allocate_entry (new_table);
895 if (new_entry == NULL)
898 new_entry->data = data;
899 new_entry->next = new_bucket->next;
900 new_bucket->next = new_entry;
904 /* Merely relink an existing entry, when moving from a
905 bucket overflow into a bucket overflow. */
906 cursor->next = new_bucket->next;
907 new_bucket->next = cursor;
912 /* Free an existing entry, when moving from a bucket
913 overflow into a bucket header. Also take care of the
914 simple case of moving from a bucket header into a bucket
916 new_bucket->data = data;
917 new_table->n_buckets_used++;
918 if (cursor != bucket)
919 free_entry (new_table, cursor);
923 free (table->bucket);
924 table->bucket = new_table->bucket;
925 table->bucket_limit = new_table->bucket_limit;
926 table->n_buckets = new_table->n_buckets;
927 table->n_buckets_used = new_table->n_buckets_used;
928 table->free_entry_list = new_table->free_entry_list;
929 /* table->n_entries already holds its value. */
931 table->entry_stack = new_table->entry_stack;
938 /* If ENTRY matches an entry already in the hash table, return the pointer
939 to the entry from the table. Otherwise, insert ENTRY and return ENTRY.
940 Return NULL if the storage required for insertion cannot be allocated.
941 This implementation does not support duplicate entries or insertion of
945 hash_insert (Hash_table *table, const void *entry)
948 struct hash_entry *bucket;
950 /* The caller cannot insert a NULL entry. */
954 /* If there's a matching entry already in the table, return that. */
955 if ((data = hash_find_entry (table, entry, &bucket, false)) != NULL)
958 /* If the growth threshold of the buckets in use has been reached, increase
959 the table size and rehash. There's no point in checking the number of
960 entries: if the hashing function is ill-conditioned, rehashing is not
961 likely to improve it. */
963 if (table->n_buckets_used
964 > table->tuning->growth_threshold * table->n_buckets)
966 /* Check more fully, before starting real work. If tuning arguments
967 became invalid, the second check will rely on proper defaults. */
968 check_tuning (table);
969 if (table->n_buckets_used
970 > table->tuning->growth_threshold * table->n_buckets)
972 const Hash_tuning *tuning = table->tuning;
974 (tuning->is_n_buckets
975 ? (table->n_buckets * tuning->growth_factor)
976 : (table->n_buckets * tuning->growth_factor
977 * tuning->growth_threshold));
979 if (SIZE_MAX <= candidate)
982 /* If the rehash fails, arrange to return NULL. */
983 if (!hash_rehash (table, candidate))
986 /* Update the bucket we are interested in. */
987 if (hash_find_entry (table, entry, &bucket, false) != NULL)
992 /* ENTRY is not matched, it should be inserted. */
996 struct hash_entry *new_entry = allocate_entry (table);
998 if (new_entry == NULL)
1001 /* Add ENTRY in the overflow of the bucket. */
1003 new_entry->data = (void *) entry;
1004 new_entry->next = bucket->next;
1005 bucket->next = new_entry;
1007 return (void *) entry;
1010 /* Add ENTRY right in the bucket head. */
1012 bucket->data = (void *) entry;
1014 table->n_buckets_used++;
1016 return (void *) entry;
1019 /* If ENTRY is already in the table, remove it and return the just-deleted
1020 data (the user may want to deallocate its storage). If ENTRY is not in the
1021 table, don't modify the table and return NULL. */
1024 hash_delete (Hash_table *table, const void *entry)
1027 struct hash_entry *bucket;
1029 data = hash_find_entry (table, entry, &bucket, true);
1036 table->n_buckets_used--;
1038 /* If the shrink threshold of the buckets in use has been reached,
1039 rehash into a smaller table. */
1041 if (table->n_buckets_used
1042 < table->tuning->shrink_threshold * table->n_buckets)
1044 /* Check more fully, before starting real work. If tuning arguments
1045 became invalid, the second check will rely on proper defaults. */
1046 check_tuning (table);
1047 if (table->n_buckets_used
1048 < table->tuning->shrink_threshold * table->n_buckets)
1050 const Hash_tuning *tuning = table->tuning;
1052 (tuning->is_n_buckets
1053 ? table->n_buckets * tuning->shrink_factor
1054 : (table->n_buckets * tuning->shrink_factor
1055 * tuning->growth_threshold));
1057 hash_rehash (table, candidate);
1070 hash_print (const Hash_table *table)
1072 struct hash_entry const *bucket;
1074 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
1076 struct hash_entry *cursor;
1079 printf ("%lu:\n", (unsigned long int) (bucket - table->bucket));
1081 for (cursor = bucket; cursor; cursor = cursor->next)
1083 char const *s = cursor->data;
1086 printf (" %s\n", s);
1091 #endif /* TESTING */