1/* hash - hashing table processing.
2
3 Copyright (C) 1998-2004, 2006-2007, 2009-2019 Free Software Foundation, Inc.
4
5 Written by Jim Meyering, 1992.
6
7 This program is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
11
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <https://www.gnu.org/licenses/>. */
19
20/* A generic hash table package. */
21
22/* Define USE_OBSTACK to 1 if you want the allocator to use obstacks instead
23 of malloc. If you change USE_OBSTACK, you have to recompile! */
24
25#include <config.h>
26
27#include "hash.h"
28
29#include "bitrotate.h"
30#include "xalloc-oversized.h"
31
32#include <stdint.h>
33#include <stdio.h>
34#include <stdlib.h>
35
36#if USE_OBSTACK
37# include "obstack.h"
38# ifndef obstack_chunk_alloc
39# define obstack_chunk_alloc malloc
40# endif
41# ifndef obstack_chunk_free
42# define obstack_chunk_free free
43# endif
44#endif
45
46struct hash_entry
47 {
48 void *data;
49 struct hash_entry *next;
50 };
51
52struct hash_table
53 {
54 /* The array of buckets starts at BUCKET and extends to BUCKET_LIMIT-1,
55 for a possibility of N_BUCKETS. Among those, N_BUCKETS_USED buckets
56 are not empty, there are N_ENTRIES active entries in the table. */
57 struct hash_entry *bucket;
58 struct hash_entry const *bucket_limit;
59 size_t n_buckets;
60 size_t n_buckets_used;
61 size_t n_entries;
62
63 /* Tuning arguments, kept in a physically separate structure. */
64 const Hash_tuning *tuning;
65
66 /* Three functions are given to 'hash_initialize', see the documentation
67 block for this function. In a word, HASHER randomizes a user entry
68 into a number up from 0 up to some maximum minus 1; COMPARATOR returns
69 true if two user entries compare equally; and DATA_FREER is the cleanup
70 function for a user entry. */
71 Hash_hasher hasher;
72 Hash_comparator comparator;
73 Hash_data_freer data_freer;
74
75 /* A linked list of freed struct hash_entry structs. */
76 struct hash_entry *free_entry_list;
77
78#if USE_OBSTACK
79 /* Whenever obstacks are used, it is possible to allocate all overflowed
80 entries into a single stack, so they all can be freed in a single
81 operation. It is not clear if the speedup is worth the trouble. */
82 struct obstack entry_stack;
83#endif
84 };
85
86/* A hash table contains many internal entries, each holding a pointer to
87 some user-provided data (also called a user entry). An entry indistinctly
88 refers to both the internal entry and its associated user entry. A user
89 entry contents may be hashed by a randomization function (the hashing
90 function, or just "hasher" for short) into a number (or "slot") between 0
91 and the current table size. At each slot position in the hash table,
92 starts a linked chain of entries for which the user data all hash to this
93 slot. A bucket is the collection of all entries hashing to the same slot.
94
95 A good "hasher" function will distribute entries rather evenly in buckets.
96 In the ideal case, the length of each bucket is roughly the number of
97 entries divided by the table size. Finding the slot for a data is usually
98 done in constant time by the "hasher", and the later finding of a precise
99 entry is linear in time with the size of the bucket. Consequently, a
100 larger hash table size (that is, a larger number of buckets) is prone to
101 yielding shorter chains, *given* the "hasher" function behaves properly.
102
103 Long buckets slow down the lookup algorithm. One might use big hash table
104 sizes in hope to reduce the average length of buckets, but this might
105 become inordinate, as unused slots in the hash table take some space. The
106 best bet is to make sure you are using a good "hasher" function (beware
107 that those are not that easy to write! :-), and to use a table size
108 larger than the actual number of entries. */
109
110/* If an insertion makes the ratio of nonempty buckets to table size larger
111 than the growth threshold (a number between 0.0 and 1.0), then increase
112 the table size by multiplying by the growth factor (a number greater than
113 1.0). The growth threshold defaults to 0.8, and the growth factor
114 defaults to 1.414, meaning that the table will have doubled its size
115 every second time 80% of the buckets get used. */
116#define DEFAULT_GROWTH_THRESHOLD 0.8f
117#define DEFAULT_GROWTH_FACTOR 1.414f
118
119/* If a deletion empties a bucket and causes the ratio of used buckets to
120 table size to become smaller than the shrink threshold (a number between
121 0.0 and 1.0), then shrink the table by multiplying by the shrink factor (a
122 number greater than the shrink threshold but smaller than 1.0). The shrink
123 threshold and factor default to 0.0 and 1.0, meaning that the table never
124 shrinks. */
125#define DEFAULT_SHRINK_THRESHOLD 0.0f
126#define DEFAULT_SHRINK_FACTOR 1.0f
127
128/* Use this to initialize or reset a TUNING structure to
129 some sensible values. */
130static const Hash_tuning default_tuning =
131 {
132 DEFAULT_SHRINK_THRESHOLD,
133 DEFAULT_SHRINK_FACTOR,
134 DEFAULT_GROWTH_THRESHOLD,
135 DEFAULT_GROWTH_FACTOR,
136 false
137 };
138
139/* Information and lookup. */
140
141/* The following few functions provide information about the overall hash
142 table organization: the number of entries, number of buckets and maximum
143 length of buckets. */
144
145/* Return the number of buckets in the hash table. The table size, the total
146 number of buckets (used plus unused), or the maximum number of slots, are
147 the same quantity. */
148
149size_t
150hash_get_n_buckets (const Hash_table *table)
151{
152 return table->n_buckets;
153}
154
155/* Return the number of slots in use (non-empty buckets). */
156
157size_t
158hash_get_n_buckets_used (const Hash_table *table)
159{
160 return table->n_buckets_used;
161}
162
163/* Return the number of active entries. */
164
165size_t
166hash_get_n_entries (const Hash_table *table)
167{
168 return table->n_entries;
169}
170
171/* Return the length of the longest chain (bucket). */
172
173size_t
174hash_get_max_bucket_length (const Hash_table *table)
175{
176 struct hash_entry const *bucket;
177 size_t max_bucket_length = 0;
178
179 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
180 {
181 if (bucket->data)
182 {
183 struct hash_entry const *cursor = bucket;
184 size_t bucket_length = 1;
185
186 while (cursor = cursor->next, cursor)
187 bucket_length++;
188
189 if (bucket_length > max_bucket_length)
190 max_bucket_length = bucket_length;
191 }
192 }
193
194 return max_bucket_length;
195}
196
197/* Do a mild validation of a hash table, by traversing it and checking two
198 statistics. */
199
200bool
201hash_table_ok (const Hash_table *table)
202{
203 struct hash_entry const *bucket;
204 size_t n_buckets_used = 0;
205 size_t n_entries = 0;
206
207 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
208 {
209 if (bucket->data)
210 {
211 struct hash_entry const *cursor = bucket;
212
213 /* Count bucket head. */
214 n_buckets_used++;
215 n_entries++;
216
217 /* Count bucket overflow. */
218 while (cursor = cursor->next, cursor)
219 n_entries++;
220 }
221 }
222
223 if (n_buckets_used == table->n_buckets_used && n_entries == table->n_entries)
224 return true;
225
226 return false;
227}
228
229void
230hash_print_statistics (const Hash_table *table, FILE *stream)
231{
232 size_t n_entries = hash_get_n_entries (table);
233 size_t n_buckets = hash_get_n_buckets (table);
234 size_t n_buckets_used = hash_get_n_buckets_used (table);
235 size_t max_bucket_length = hash_get_max_bucket_length (table);
236
237 fprintf (stream, "# entries: %lu\n", (unsigned long int) n_entries);
238 fprintf (stream, "# buckets: %lu\n", (unsigned long int) n_buckets);
239 fprintf (stream, "# buckets used: %lu (%.2f%%)\n",
240 (unsigned long int) n_buckets_used,
241 (100.0 * n_buckets_used) / n_buckets);
242 fprintf (stream, "max bucket length: %lu\n",
243 (unsigned long int) max_bucket_length);
244}
245
246/* Hash KEY and return a pointer to the selected bucket.
247 If TABLE->hasher misbehaves, abort. */
248static struct hash_entry *
249safe_hasher (const Hash_table *table, const void *key)
250{
251 size_t n = table->hasher (key, table->n_buckets);
252 if (! (n < table->n_buckets))
253 abort ();
254 return table->bucket + n;
255}
256
257/* If ENTRY matches an entry already in the hash table, return the
258 entry from the table. Otherwise, return NULL. */
259
260void *
261hash_lookup (const Hash_table *table, const void *entry)
262{
263 struct hash_entry const *bucket = safe_hasher (table, entry);
264 struct hash_entry const *cursor;
265
266 if (bucket->data == NULL)
267 return NULL;
268
269 for (cursor = bucket; cursor; cursor = cursor->next)
270 if (entry == cursor->data || table->comparator (entry, cursor->data))
271 return cursor->data;
272
273 return NULL;
274}
275
276/* Walking. */
277
278/* The functions in this page traverse the hash table and process the
279 contained entries. For the traversal to work properly, the hash table
280 should not be resized nor modified while any particular entry is being
281 processed. In particular, entries should not be added, and an entry
282 may be removed only if there is no shrink threshold and the entry being
283 removed has already been passed to hash_get_next. */
284
285/* Return the first data in the table, or NULL if the table is empty. */
286
287void *
288hash_get_first (const Hash_table *table)
289{
290 struct hash_entry const *bucket;
291
292 if (table->n_entries == 0)
293 return NULL;
294
295 for (bucket = table->bucket; ; bucket++)
296 if (! (bucket < table->bucket_limit))
297 abort ();
298 else if (bucket->data)
299 return bucket->data;
300}
301
302/* Return the user data for the entry following ENTRY, where ENTRY has been
303 returned by a previous call to either 'hash_get_first' or 'hash_get_next'.
304 Return NULL if there are no more entries. */
305
306void *
307hash_get_next (const Hash_table *table, const void *entry)
308{
309 struct hash_entry const *bucket = safe_hasher (table, entry);
310 struct hash_entry const *cursor;
311
312 /* Find next entry in the same bucket. */
313 cursor = bucket;
314 do
315 {
316 if (cursor->data == entry && cursor->next)
317 return cursor->next->data;
318 cursor = cursor->next;
319 }
320 while (cursor != NULL);
321
322 /* Find first entry in any subsequent bucket. */
323 while (++bucket < table->bucket_limit)
324 if (bucket->data)
325 return bucket->data;
326
327 /* None found. */
328 return NULL;
329}
330
331/* Fill BUFFER with pointers to active user entries in the hash table, then
332 return the number of pointers copied. Do not copy more than BUFFER_SIZE
333 pointers. */
334
335size_t
336hash_get_entries (const Hash_table *table, void **buffer,
337 size_t buffer_size)
338{
339 size_t counter = 0;
340 struct hash_entry const *bucket;
341 struct hash_entry const *cursor;
342
343 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
344 {
345 if (bucket->data)
346 {
347 for (cursor = bucket; cursor; cursor = cursor->next)
348 {
349 if (counter >= buffer_size)
350 return counter;
351 buffer[counter++] = cursor->data;
352 }
353 }
354 }
355
356 return counter;
357}
358
359/* Call a PROCESSOR function for each entry of a hash table, and return the
360 number of entries for which the processor function returned success. A
361 pointer to some PROCESSOR_DATA which will be made available to each call to
362 the processor function. The PROCESSOR accepts two arguments: the first is
363 the user entry being walked into, the second is the value of PROCESSOR_DATA
364 as received. The walking continue for as long as the PROCESSOR function
365 returns nonzero. When it returns zero, the walking is interrupted. */
366
367size_t
368hash_do_for_each (const Hash_table *table, Hash_processor processor,
369 void *processor_data)
370{
371 size_t counter = 0;
372 struct hash_entry const *bucket;
373 struct hash_entry const *cursor;
374
375 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
376 {
377 if (bucket->data)
378 {
379 for (cursor = bucket; cursor; cursor = cursor->next)
380 {
381 if (! processor (cursor->data, processor_data))
382 return counter;
383 counter++;
384 }
385 }
386 }
387
388 return counter;
389}
390
391/* Allocation and clean-up. */
392
393/* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1.
394 This is a convenience routine for constructing other hashing functions. */
395
396#if USE_DIFF_HASH
397
398/* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see
399 B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,
400 Software--practice & experience 20, 2 (Feb 1990), 209-224. Good hash
401 algorithms tend to be domain-specific, so what's good for [diffutils'] io.c
402 may not be good for your application." */
403
404size_t
405hash_string (const char *string, size_t n_buckets)
406{
407# define HASH_ONE_CHAR(Value, Byte) \
408 ((Byte) + rotl_sz (Value, 7))
409
410 size_t value = 0;
411 unsigned char ch;
412
413 for (; (ch = *string); string++)
414 value = HASH_ONE_CHAR (value, ch);
415 return value % n_buckets;
416
417# undef HASH_ONE_CHAR
418}
419
420#else /* not USE_DIFF_HASH */
421
422/* This one comes from 'recode', and performs a bit better than the above as
423 per a few experiments. It is inspired from a hashing routine found in the
424 very old Cyber 'snoop', itself written in typical Greg Mansfield style.
425 (By the way, what happened to this excellent man? Is he still alive?) */
426
427size_t
428hash_string (const char *string, size_t n_buckets)
429{
430 size_t value = 0;
431 unsigned char ch;
432
433 for (; (ch = *string); string++)
434 value = (value * 31 + ch) % n_buckets;
435 return value;
436}
437
438#endif /* not USE_DIFF_HASH */
439
440/* Return true if CANDIDATE is a prime number. CANDIDATE should be an odd
441 number at least equal to 11. */
442
443static bool _GL_ATTRIBUTE_CONST
444is_prime (size_t candidate)
445{
446 size_t divisor = 3;
447 size_t square = divisor * divisor;
448
449 while (square < candidate && (candidate % divisor))
450 {
451 divisor++;
452 square += 4 * divisor;
453 divisor++;
454 }
455
456 return (candidate % divisor ? true : false);
457}
458
459/* Round a given CANDIDATE number up to the nearest prime, and return that
460 prime. Primes lower than 10 are merely skipped. */
461
462static size_t _GL_ATTRIBUTE_CONST
463next_prime (size_t candidate)
464{
465 /* Skip small primes. */
466 if (candidate < 10)
467 candidate = 10;
468
469 /* Make it definitely odd. */
470 candidate |= 1;
471
472 while (SIZE_MAX != candidate && !is_prime (candidate))
473 candidate += 2;
474
475 return candidate;
476}
477
478void
479hash_reset_tuning (Hash_tuning *tuning)
480{
481 *tuning = default_tuning;
482}
483
484/* If the user passes a NULL hasher, we hash the raw pointer. */
485static size_t
486raw_hasher (const void *data, size_t n)
487{
488 /* When hashing unique pointers, it is often the case that they were
489 generated by malloc and thus have the property that the low-order
490 bits are 0. As this tends to give poorer performance with small
491 tables, we rotate the pointer value before performing division,
492 in an attempt to improve hash quality. */
493 size_t val = rotr_sz ((size_t) data, 3);
494 return val % n;
495}
496
497/* If the user passes a NULL comparator, we use pointer comparison. */
498static bool
499raw_comparator (const void *a, const void *b)
500{
501 return a == b;
502}
503
504
505/* For the given hash TABLE, check the user supplied tuning structure for
506 reasonable values, and return true if there is no gross error with it.
507 Otherwise, definitively reset the TUNING field to some acceptable default
508 in the hash table (that is, the user loses the right of further modifying
509 tuning arguments), and return false. */
510
511static bool
512check_tuning (Hash_table *table)
513{
514 const Hash_tuning *tuning = table->tuning;
515 float epsilon;
516 if (tuning == &default_tuning)
517 return true;
518
519 /* Be a bit stricter than mathematics would require, so that
520 rounding errors in size calculations do not cause allocations to
521 fail to grow or shrink as they should. The smallest allocation
522 is 11 (due to next_prime's algorithm), so an epsilon of 0.1
523 should be good enough. */
524 epsilon = 0.1f;
525
526 if (epsilon < tuning->growth_threshold
527 && tuning->growth_threshold < 1 - epsilon
528 && 1 + epsilon < tuning->growth_factor
529 && 0 <= tuning->shrink_threshold
530 && tuning->shrink_threshold + epsilon < tuning->shrink_factor
531 && tuning->shrink_factor <= 1
532 && tuning->shrink_threshold + epsilon < tuning->growth_threshold)
533 return true;
534
535 table->tuning = &default_tuning;
536 return false;
537}
538
539/* Compute the size of the bucket array for the given CANDIDATE and
540 TUNING, or return 0 if there is no possible way to allocate that
541 many entries. */
542
543static size_t _GL_ATTRIBUTE_PURE
544compute_bucket_size (size_t candidate, const Hash_tuning *tuning)
545{
546 if (!tuning->is_n_buckets)
547 {
548 float new_candidate = candidate / tuning->growth_threshold;
549 if (SIZE_MAX <= new_candidate)
550 return 0;
551 candidate = new_candidate;
552 }
553 candidate = next_prime (candidate);
554 if (xalloc_oversized (candidate, sizeof (struct hash_entry *)))
555 return 0;
556 return candidate;
557}
558
559/* Allocate and return a new hash table, or NULL upon failure. The initial
560 number of buckets is automatically selected so as to _guarantee_ that you
561 may insert at least CANDIDATE different user entries before any growth of
562 the hash table size occurs. So, if have a reasonably tight a-priori upper
563 bound on the number of entries you intend to insert in the hash table, you
564 may save some table memory and insertion time, by specifying it here. If
565 the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
566 argument has its meaning changed to the wanted number of buckets.
567
568 TUNING points to a structure of user-supplied values, in case some fine
569 tuning is wanted over the default behavior of the hasher. If TUNING is
570 NULL, the default tuning parameters are used instead. If TUNING is
571 provided but the values requested are out of bounds or might cause
572 rounding errors, return NULL.
573
574 The user-supplied HASHER function, when not NULL, accepts two
575 arguments ENTRY and TABLE_SIZE. It computes, by hashing ENTRY contents, a
576 slot number for that entry which should be in the range 0..TABLE_SIZE-1.
577 This slot number is then returned.
578
579 The user-supplied COMPARATOR function, when not NULL, accepts two
580 arguments pointing to user data, it then returns true for a pair of entries
581 that compare equal, or false otherwise. This function is internally called
582 on entries which are already known to hash to the same bucket index,
583 but which are distinct pointers.
584
585 The user-supplied DATA_FREER function, when not NULL, may be later called
586 with the user data as an argument, just before the entry containing the
587 data gets freed. This happens from within 'hash_free' or 'hash_clear'.
588 You should specify this function only if you want these functions to free
589 all of your 'data' data. This is typically the case when your data is
590 simply an auxiliary struct that you have malloc'd to aggregate several
591 values. */
592
593Hash_table *
594hash_initialize (size_t candidate, const Hash_tuning *tuning,
595 Hash_hasher hasher, Hash_comparator comparator,
596 Hash_data_freer data_freer)
597{
598 Hash_table *table;
599
600 if (hasher == NULL)
601 hasher = raw_hasher;
602 if (comparator == NULL)
603 comparator = raw_comparator;
604
605 table = malloc (sizeof *table);
606 if (table == NULL)
607 return NULL;
608
609 if (!tuning)
610 tuning = &default_tuning;
611 table->tuning = tuning;
612 if (!check_tuning (table))
613 {
614 /* Fail if the tuning options are invalid. This is the only occasion
615 when the user gets some feedback about it. Once the table is created,
616 if the user provides invalid tuning options, we silently revert to
617 using the defaults, and ignore further request to change the tuning
618 options. */
619 goto fail;
620 }
621
622 table->n_buckets = compute_bucket_size (candidate, tuning);
623 if (!table->n_buckets)
624 goto fail;
625
626 table->bucket = calloc (table->n_buckets, sizeof *table->bucket);
627 if (table->bucket == NULL)
628 goto fail;
629 table->bucket_limit = table->bucket + table->n_buckets;
630 table->n_buckets_used = 0;
631 table->n_entries = 0;
632
633 table->hasher = hasher;
634 table->comparator = comparator;
635 table->data_freer = data_freer;
636
637 table->free_entry_list = NULL;
638#if USE_OBSTACK
639 obstack_init (&table->entry_stack);
640#endif
641 return table;
642
643 fail:
644 free (table);
645 return NULL;
646}
647
648/* Make all buckets empty, placing any chained entries on the free list.
649 Apply the user-specified function data_freer (if any) to the datas of any
650 affected entries. */
651
652void
653hash_clear (Hash_table *table)
654{
655 struct hash_entry *bucket;
656
657 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
658 {
659 if (bucket->data)
660 {
661 struct hash_entry *cursor;
662 struct hash_entry *next;
663
664 /* Free the bucket overflow. */
665 for (cursor = bucket->next; cursor; cursor = next)
666 {
667 if (table->data_freer)
668 table->data_freer (cursor->data);
669 cursor->data = NULL;
670
671 next = cursor->next;
672 /* Relinking is done one entry at a time, as it is to be expected
673 that overflows are either rare or short. */
674 cursor->next = table->free_entry_list;
675 table->free_entry_list = cursor;
676 }
677
678 /* Free the bucket head. */
679 if (table->data_freer)
680 table->data_freer (bucket->data);
681 bucket->data = NULL;
682 bucket->next = NULL;
683 }
684 }
685
686 table->n_buckets_used = 0;
687 table->n_entries = 0;
688}
689
690/* Reclaim all storage associated with a hash table. If a data_freer
691 function has been supplied by the user when the hash table was created,
692 this function applies it to the data of each entry before freeing that
693 entry. */
694
695void
696hash_free (Hash_table *table)
697{
698 struct hash_entry *bucket;
699 struct hash_entry *cursor;
700 struct hash_entry *next;
701
702 /* Call the user data_freer function. */
703 if (table->data_freer && table->n_entries)
704 {
705 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
706 {
707 if (bucket->data)
708 {
709 for (cursor = bucket; cursor; cursor = cursor->next)
710 table->data_freer (cursor->data);
711 }
712 }
713 }
714
715#if USE_OBSTACK
716
717 obstack_free (&table->entry_stack, NULL);
718
719#else
720
721 /* Free all bucket overflowed entries. */
722 for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
723 {
724 for (cursor = bucket->next; cursor; cursor = next)
725 {
726 next = cursor->next;
727 free (cursor);
728 }
729 }
730
731 /* Also reclaim the internal list of previously freed entries. */
732 for (cursor = table->free_entry_list; cursor; cursor = next)
733 {
734 next = cursor->next;
735 free (cursor);
736 }
737
738#endif
739
740 /* Free the remainder of the hash table structure. */
741 free (table->bucket);
742 free (table);
743}
744
745/* Insertion and deletion. */
746
747/* Get a new hash entry for a bucket overflow, possibly by recycling a
748 previously freed one. If this is not possible, allocate a new one. */
749
750static struct hash_entry *
751allocate_entry (Hash_table *table)
752{
753 struct hash_entry *new;
754
755 if (table->free_entry_list)
756 {
757 new = table->free_entry_list;
758 table->free_entry_list = new->next;
759 }
760 else
761 {
762#if USE_OBSTACK
763 new = obstack_alloc (&table->entry_stack, sizeof *new);
764#else
765 new = malloc (sizeof *new);
766#endif
767 }
768
769 return new;
770}
771
772/* Free a hash entry which was part of some bucket overflow,
773 saving it for later recycling. */
774
775static void
776free_entry (Hash_table *table, struct hash_entry *entry)
777{
778 entry->data = NULL;
779 entry->next = table->free_entry_list;
780 table->free_entry_list = entry;
781}
782
783/* This private function is used to help with insertion and deletion. When
784 ENTRY matches an entry in the table, return a pointer to the corresponding
785 user data and set *BUCKET_HEAD to the head of the selected bucket.
786 Otherwise, return NULL. When DELETE is true and ENTRY matches an entry in
787 the table, unlink the matching entry. */
788
789static void *
790hash_find_entry (Hash_table *table, const void *entry,
791 struct hash_entry **bucket_head, bool delete)
792{
793 struct hash_entry *bucket = safe_hasher (table, entry);
794 struct hash_entry *cursor;
795
796 *bucket_head = bucket;
797
798 /* Test for empty bucket. */
799 if (bucket->data == NULL)
800 return NULL;
801
802 /* See if the entry is the first in the bucket. */
803 if (entry == bucket->data || table->comparator (entry, bucket->data))
804 {
805 void *data = bucket->data;
806
807 if (delete)
808 {
809 if (bucket->next)
810 {
811 struct hash_entry *next = bucket->next;
812
813 /* Bump the first overflow entry into the bucket head, then save
814 the previous first overflow entry for later recycling. */
815 *bucket = *next;
816 free_entry (table, next);
817 }
818 else
819 {
820 bucket->data = NULL;
821 }
822 }
823
824 return data;
825 }
826
827 /* Scan the bucket overflow. */
828 for (cursor = bucket; cursor->next; cursor = cursor->next)
829 {
830 if (entry == cursor->next->data
831 || table->comparator (entry, cursor->next->data))
832 {
833 void *data = cursor->next->data;
834
835 if (delete)
836 {
837 struct hash_entry *next = cursor->next;
838
839 /* Unlink the entry to delete, then save the freed entry for later
840 recycling. */
841 cursor->next = next->next;
842 free_entry (table, next);
843 }
844
845 return data;
846 }
847 }
848
849 /* No entry found. */
850 return NULL;
851}
852
853/* Internal helper, to move entries from SRC to DST. Both tables must
854 share the same free entry list. If SAFE, only move overflow
855 entries, saving bucket heads for later, so that no allocations will
856 occur. Return false if the free entry list is exhausted and an
857 allocation fails. */
858
859static bool
860transfer_entries (Hash_table *dst, Hash_table *src, bool safe)
861{
862 struct hash_entry *bucket;
863 struct hash_entry *cursor;
864 struct hash_entry *next;
865 for (bucket = src->bucket; bucket < src->bucket_limit; bucket++)
866 if (bucket->data)
867 {
868 void *data;
869 struct hash_entry *new_bucket;
870
871 /* Within each bucket, transfer overflow entries first and
872 then the bucket head, to minimize memory pressure. After
873 all, the only time we might allocate is when moving the
874 bucket head, but moving overflow entries first may create
875 free entries that can be recycled by the time we finally
876 get to the bucket head. */
877 for (cursor = bucket->next; cursor; cursor = next)
878 {
879 data = cursor->data;
880 new_bucket = safe_hasher (dst, data);
881
882 next = cursor->next;
883
884 if (new_bucket->data)
885 {
886 /* Merely relink an existing entry, when moving from a
887 bucket overflow into a bucket overflow. */
888 cursor->next = new_bucket->next;
889 new_bucket->next = cursor;
890 }
891 else
892 {
893 /* Free an existing entry, when moving from a bucket
894 overflow into a bucket header. */
895 new_bucket->data = data;
896 dst->n_buckets_used++;
897 free_entry (dst, cursor);
898 }
899 }
900 /* Now move the bucket head. Be sure that if we fail due to
901 allocation failure that the src table is in a consistent
902 state. */
903 data = bucket->data;
904 bucket->next = NULL;
905 if (safe)
906 continue;
907 new_bucket = safe_hasher (dst, data);
908
909 if (new_bucket->data)
910 {
911 /* Allocate or recycle an entry, when moving from a bucket
912 header into a bucket overflow. */
913 struct hash_entry *new_entry = allocate_entry (dst);
914
915 if (new_entry == NULL)
916 return false;
917
918 new_entry->data = data;
919 new_entry->next = new_bucket->next;
920 new_bucket->next = new_entry;
921 }
922 else
923 {
924 /* Move from one bucket header to another. */
925 new_bucket->data = data;
926 dst->n_buckets_used++;
927 }
928 bucket->data = NULL;
929 src->n_buckets_used--;
930 }
931 return true;
932}
933
934/* For an already existing hash table, change the number of buckets through
935 specifying CANDIDATE. The contents of the hash table are preserved. The
936 new number of buckets is automatically selected so as to _guarantee_ that
937 the table may receive at least CANDIDATE different user entries, including
938 those already in the table, before any other growth of the hash table size
939 occurs. If TUNING->IS_N_BUCKETS is true, then CANDIDATE specifies the
940 exact number of buckets desired. Return true iff the rehash succeeded. */
941
942bool
943hash_rehash (Hash_table *table, size_t candidate)
944{
945 Hash_table storage;
946 Hash_table *new_table;
947 size_t new_size = compute_bucket_size (candidate, table->tuning);
948
949 if (!new_size)
950 return false;
951 if (new_size == table->n_buckets)
952 return true;
953 new_table = &storage;
954 new_table->bucket = calloc (new_size, sizeof *new_table->bucket);
955 if (new_table->bucket == NULL)
956 return false;
957 new_table->n_buckets = new_size;
958 new_table->bucket_limit = new_table->bucket + new_size;
959 new_table->n_buckets_used = 0;
960 new_table->n_entries = 0;
961 new_table->tuning = table->tuning;
962 new_table->hasher = table->hasher;
963 new_table->comparator = table->comparator;
964 new_table->data_freer = table->data_freer;
965
966 /* In order for the transfer to successfully complete, we need
967 additional overflow entries when distinct buckets in the old
968 table collide into a common bucket in the new table. The worst
969 case possible is a hasher that gives a good spread with the old
970 size, but returns a constant with the new size; if we were to
971 guarantee table->n_buckets_used-1 free entries in advance, then
972 the transfer would be guaranteed to not allocate memory.
973 However, for large tables, a guarantee of no further allocation
974 introduces a lot of extra memory pressure, all for an unlikely
975 corner case (most rehashes reduce, rather than increase, the
976 number of overflow entries needed). So, we instead ensure that
977 the transfer process can be reversed if we hit a memory
978 allocation failure mid-transfer. */
979
980 /* Merely reuse the extra old space into the new table. */
981#if USE_OBSTACK
982 new_table->entry_stack = table->entry_stack;
983#endif
984 new_table->free_entry_list = table->free_entry_list;
985
986 if (transfer_entries (new_table, table, false))
987 {
988 /* Entries transferred successfully; tie up the loose ends. */
989 free (table->bucket);
990 table->bucket = new_table->bucket;
991 table->bucket_limit = new_table->bucket_limit;
992 table->n_buckets = new_table->n_buckets;
993 table->n_buckets_used = new_table->n_buckets_used;
994 table->free_entry_list = new_table->free_entry_list;
995 /* table->n_entries and table->entry_stack already hold their value. */
996 return true;
997 }
998
999 /* We've allocated new_table->bucket (and possibly some entries),
1000 exhausted the free list, and moved some but not all entries into
1001 new_table. We must undo the partial move before returning
1002 failure. The only way to get into this situation is if new_table
1003 uses fewer buckets than the old table, so we will reclaim some
1004 free entries as overflows in the new table are put back into
1005 distinct buckets in the old table.
1006
1007 There are some pathological cases where a single pass through the
1008 table requires more intermediate overflow entries than using two
1009 passes. Two passes give worse cache performance and takes
1010 longer, but at this point, we're already out of memory, so slow
1011 and safe is better than failure. */
1012 table->free_entry_list = new_table->free_entry_list;
1013 if (! (transfer_entries (table, new_table, true)
1014 && transfer_entries (table, new_table, false)))
1015 abort ();
1016 /* table->n_entries already holds its value. */
1017 free (new_table->bucket);
1018 return false;
1019}
1020
1021/* Insert ENTRY into hash TABLE if there is not already a matching entry.
1022
1023 Return -1 upon memory allocation failure.
1024 Return 1 if insertion succeeded.
1025 Return 0 if there is already a matching entry in the table,
1026 and in that case, if MATCHED_ENT is non-NULL, set *MATCHED_ENT
1027 to that entry.
1028
1029 This interface is easier to use than hash_insert when you must
1030 distinguish between the latter two cases. More importantly,
1031 hash_insert is unusable for some types of ENTRY values. When using
1032 hash_insert, the only way to distinguish those cases is to compare
1033 the return value and ENTRY. That works only when you can have two
1034 different ENTRY values that point to data that compares "equal". Thus,
1035 when the ENTRY value is a simple scalar, you must use
1036 hash_insert_if_absent. ENTRY must not be NULL. */
1037int
1038hash_insert_if_absent (Hash_table *table, void const *entry,
1039 void const **matched_ent)
1040{
1041 void *data;
1042 struct hash_entry *bucket;
1043
1044 /* The caller cannot insert a NULL entry, since hash_lookup returns NULL
1045 to indicate "not found", and hash_find_entry uses "bucket->data == NULL"
1046 to indicate an empty bucket. */
1047 if (! entry)
1048 abort ();
1049
1050 /* If there's a matching entry already in the table, return that. */
1051 if ((data = hash_find_entry (table, entry, &bucket, false)) != NULL)
1052 {
1053 if (matched_ent)
1054 *matched_ent = data;
1055 return 0;
1056 }
1057
1058 /* If the growth threshold of the buckets in use has been reached, increase
1059 the table size and rehash. There's no point in checking the number of
1060 entries: if the hashing function is ill-conditioned, rehashing is not
1061 likely to improve it. */
1062
1063 if (table->n_buckets_used
1064 > table->tuning->growth_threshold * table->n_buckets)
1065 {
1066 /* Check more fully, before starting real work. If tuning arguments
1067 became invalid, the second check will rely on proper defaults. */
1068 check_tuning (table);
1069 if (table->n_buckets_used
1070 > table->tuning->growth_threshold * table->n_buckets)
1071 {
1072 const Hash_tuning *tuning = table->tuning;
1073 float candidate =
1074 (tuning->is_n_buckets
1075 ? (table->n_buckets * tuning->growth_factor)
1076 : (table->n_buckets * tuning->growth_factor
1077 * tuning->growth_threshold));
1078
1079 if (SIZE_MAX <= candidate)
1080 return -1;
1081
1082 /* If the rehash fails, arrange to return NULL. */
1083 if (!hash_rehash (table, candidate))
1084 return -1;
1085
1086 /* Update the bucket we are interested in. */
1087 if (hash_find_entry (table, entry, &bucket, false) != NULL)
1088 abort ();
1089 }
1090 }
1091
1092 /* ENTRY is not matched, it should be inserted. */
1093
1094 if (bucket->data)
1095 {
1096 struct hash_entry *new_entry = allocate_entry (table);
1097
1098 if (new_entry == NULL)
1099 return -1;
1100
1101 /* Add ENTRY in the overflow of the bucket. */
1102
1103 new_entry->data = (void *) entry;
1104 new_entry->next = bucket->next;
1105 bucket->next = new_entry;
1106 table->n_entries++;
1107 return 1;
1108 }
1109
1110 /* Add ENTRY right in the bucket head. */
1111
1112 bucket->data = (void *) entry;
1113 table->n_entries++;
1114 table->n_buckets_used++;
1115
1116 return 1;
1117}
1118
1119/* If ENTRY matches an entry already in the hash table, return the pointer
1120 to the entry from the table. Otherwise, insert ENTRY and return ENTRY.
1121 Return NULL if the storage required for insertion cannot be allocated.
1122 This implementation does not support duplicate entries or insertion of
1123 NULL. */
1124
1125void *
1126hash_insert (Hash_table *table, void const *entry)
1127{
1128 void const *matched_ent;
1129 int err = hash_insert_if_absent (table, entry, &matched_ent);
1130 return (err == -1
1131 ? NULL
1132 : (void *) (err == 0 ? matched_ent : entry));
1133}
1134
1135/* If ENTRY is already in the table, remove it and return the just-deleted
1136 data (the user may want to deallocate its storage). If ENTRY is not in the
1137 table, don't modify the table and return NULL. */
1138
1139void *
1140hash_delete (Hash_table *table, const void *entry)
1141{
1142 void *data;
1143 struct hash_entry *bucket;
1144
1145 data = hash_find_entry (table, entry, &bucket, true);
1146 if (!data)
1147 return NULL;
1148
1149 table->n_entries--;
1150 if (!bucket->data)
1151 {
1152 table->n_buckets_used--;
1153
1154 /* If the shrink threshold of the buckets in use has been reached,
1155 rehash into a smaller table. */
1156
1157 if (table->n_buckets_used
1158 < table->tuning->shrink_threshold * table->n_buckets)
1159 {
1160 /* Check more fully, before starting real work. If tuning arguments
1161 became invalid, the second check will rely on proper defaults. */
1162 check_tuning (table);
1163 if (table->n_buckets_used
1164 < table->tuning->shrink_threshold * table->n_buckets)
1165 {
1166 const Hash_tuning *tuning = table->tuning;
1167 size_t candidate =
1168 (tuning->is_n_buckets
1169 ? table->n_buckets * tuning->shrink_factor
1170 : (table->n_buckets * tuning->shrink_factor
1171 * tuning->growth_threshold));
1172
1173 if (!hash_rehash (table, candidate))
1174 {
1175 /* Failure to allocate memory in an attempt to
1176 shrink the table is not fatal. But since memory
1177 is low, we can at least be kind and free any
1178 spare entries, rather than keeping them tied up
1179 in the free entry list. */
1180#if ! USE_OBSTACK
1181 struct hash_entry *cursor = table->free_entry_list;
1182 struct hash_entry *next;
1183 while (cursor)
1184 {
1185 next = cursor->next;
1186 free (cursor);
1187 cursor = next;
1188 }
1189 table->free_entry_list = NULL;
1190#endif
1191 }
1192 }
1193 }
1194 }
1195
1196 return data;
1197}
1198
1199/* Testing. */
1200
1201#if TESTING
1202
1203void
1204hash_print (const Hash_table *table)
1205{
1206 struct hash_entry *bucket = (struct hash_entry *) table->bucket;
1207
1208 for ( ; bucket < table->bucket_limit; bucket++)
1209 {
1210 struct hash_entry *cursor;
1211
1212 if (bucket)
1213 printf ("%lu:\n", (unsigned long int) (bucket - table->bucket));
1214
1215 for (cursor = bucket; cursor; cursor = cursor->next)
1216 {
1217 char const *s = cursor->data;
1218 /* FIXME */
1219 if (s)
1220 printf (" %s\n", s);
1221 }
1222 }
1223}
1224
1225#endif /* TESTING */
1226