2 Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free
3 Software Foundation, Inc.
5 This file is part of GNU Wget.
7 GNU Wget 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 (at
10 your option) any later version.
12 GNU Wget 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.
17 You should have received a copy of the GNU General Public License
18 along with Wget. If not, see <http://www.gnu.org/licenses/>.
20 Additional permission under GNU GPL version 3 section 7
22 If you modify this program, or any covered work, by linking or
23 combining it with the OpenSSL project's OpenSSL library (or a
24 modified version of that library), containing parts covered by the
25 terms of the OpenSSL or SSLeay licenses, the Free Software Foundation
26 grants you additional permission to convey the resulting work.
27 Corresponding Source for a non-source form of such a combination
28 shall include the source code for the parts of OpenSSL used as well
29 as that of the covered work. */
31 /* With -DSTANDALONE, this file can be compiled outside Wget source
32 tree. To test, also use -DTEST. */
45 /* Get Wget's utility headers. */
49 /* Make do without them. */
50 # define xnew(x) xmalloc (sizeof (x))
51 # define xnew_array(type, x) xmalloc (sizeof (type) * (x))
52 # define xmalloc malloc
55 # define countof(x) (sizeof (x) / sizeof ((x)[0]))
58 # define TOLOWER(x) tolower ((unsigned char) (x))
59 # if __STDC_VERSION__ >= 199901L
60 # include <stdint.h> /* for uintptr_t */
62 typedef unsigned long uintptr_t;
70 Hash tables are a technique used to implement mapping between
71 objects with near-constant-time access and storage. The table
72 associates keys to values, and a value can be very quickly
73 retrieved by providing the key. Fast lookup tables are typically
74 implemented as hash tables.
77 hash_table_new -- creates the table.
78 hash_table_destroy -- destroys the table.
79 hash_table_put -- establishes or updates key->value mapping.
80 hash_table_get -- retrieves value of key.
81 hash_table_get_pair -- get key/value pair for key.
82 hash_table_contains -- test whether the table contains key.
83 hash_table_remove -- remove key->value mapping for given key.
84 hash_table_for_each -- call function for each table entry.
85 hash_table_iterate -- iterate over entries in hash table.
86 hash_table_iter_next -- return next element during iteration.
87 hash_table_clear -- clear hash table contents.
88 hash_table_count -- return the number of entries in the table.
90 The hash table grows internally as new entries are added and is not
91 limited in size, except by available memory. The table doubles
92 with each resize, which ensures that the amortized time per
93 operation remains constant.
95 If not instructed otherwise, tables created by hash_table_new
96 consider the keys to be equal if their pointer values are the same.
97 You can use make_string_hash_table to create tables whose keys are
98 considered equal if their string contents are the same. In the
99 general case, the criterion of equality used to compare keys is
100 specified at table creation time with two callback functions,
101 "hash" and "test". The hash function transforms the key into an
102 arbitrary number that must be the same for two equal keys. The
103 test function accepts two keys and returns non-zero if they are to
106 Note that neither keys nor values are copied when inserted into the
107 hash table, so they must exist for the lifetime of the table. This
108 means that e.g. the use of static strings is OK, but objects with a
109 shorter life-time probably need to be copied (with strdup() or the
110 like in the case of strings) before being inserted. */
114 The hash table is implemented as an open-addressed table with
115 linear probing collision resolution.
117 The above means that all the cells (each cell containing a key and
118 a value pointer) are stored in a contiguous array. Array position
119 of each cell is determined by the hash value of its key and the
120 size of the table: location := hash(key) % size. If two different
121 keys end up on the same position (collide), the one that came
122 second is stored in the first unoccupied cell that follows it.
123 This collision resolution technique is called "linear probing".
125 There are more advanced collision resolution methods (quadratic
126 probing, double hashing), but we don't use them because they incur
127 more non-sequential access to the array, which results in worse CPU
128 cache behavior. Linear probing works well as long as the
129 count/size ratio (fullness) is kept below 75%. We make sure to
130 grow and rehash the table whenever this threshold is exceeded.
132 Collisions complicate deletion because simply clearing a cell
133 followed by previously collided entries would cause those neighbors
134 to not be picked up by find_cell later. One solution is to leave a
135 "tombstone" marker instead of clearing the cell, and another is to
136 recalculate the positions of adjacent cells. We take the latter
137 approach because it results in less bookkeeping garbage and faster
138 retrieval at the (slight) expense of deletion. */
140 /* Maximum allowed fullness: when hash table's fullness exceeds this
141 value, the table is resized. */
142 #define HASH_MAX_FULLNESS 0.75
144 /* The hash table size is multiplied by this factor (and then rounded
145 to the next prime) with each resize. This guarantees infrequent
147 #define HASH_RESIZE_FACTOR 2
154 typedef unsigned long (*hashfun_t) (const void *);
155 typedef int (*testfun_t) (const void *, const void *);
158 hashfun_t hash_function;
159 testfun_t test_function;
161 struct cell *cells; /* contiguous array of cells. */
162 int size; /* size of the array. */
164 int count; /* number of occupied entries. */
165 int resize_threshold; /* after size exceeds this number of
166 entries, resize the table. */
167 int prime_offset; /* the offset of the current prime in
171 /* We use the all-bits-set constant (INVALID_PTR) marker to mean that
172 a cell is empty. It is unaligned and therefore illegal as a
173 pointer. INVALID_PTR_CHAR (0xff) is the single-character constant
174 used to initialize the entire cells array as empty.
176 The all-bits-set value is a better choice than NULL because it
177 allows the use of NULL/0 keys. Since the keys are either integers
178 or pointers, the only key that cannot be used is the integer value
179 -1. This is acceptable because it still allows the use of
180 nonnegative integer keys. */
182 #define INVALID_PTR ((void *) ~(uintptr_t) 0)
184 # define UCHAR_MAX 0xff
186 #define INVALID_PTR_CHAR UCHAR_MAX
188 /* Whether the cell C is occupied (non-empty). */
189 #define CELL_OCCUPIED(c) ((c)->key != INVALID_PTR)
191 /* Clear the cell C, i.e. mark it as empty (unoccupied). */
192 #define CLEAR_CELL(c) ((c)->key = INVALID_PTR)
194 /* "Next" cell is the cell following C, but wrapping back to CELLS
195 when C would reach CELLS+SIZE. */
196 #define NEXT_CELL(c, cells, size) (c != cells + (size - 1) ? c + 1 : cells)
198 /* Loop over occupied cells starting at C, terminating the loop when
199 an empty cell is encountered. */
200 #define FOREACH_OCCUPIED_ADJACENT(c, cells, size) \
201 for (; CELL_OCCUPIED (c); c = NEXT_CELL (c, cells, size))
203 /* Return the position of KEY in hash table SIZE large, hash function
205 #define HASH_POSITION(key, hashfun, size) ((hashfun) (key) % size)
207 /* Find a prime near, but greather than or equal to SIZE. The primes
208 are looked up from a table with a selection of primes convenient
211 PRIME_OFFSET is a minor optimization: it specifies start position
212 for the search for the large enough prime. The final offset is
213 stored in the same variable. That way the list of primes does not
214 have to be scanned from the beginning each time around. */
217 prime_size (int size, int *prime_offset)
219 static const int primes[] = {
220 13, 19, 29, 41, 59, 79, 107, 149, 197, 263, 347, 457, 599, 787, 1031,
221 1361, 1777, 2333, 3037, 3967, 5167, 6719, 8737, 11369, 14783,
222 19219, 24989, 32491, 42257, 54941, 71429, 92861, 120721, 156941,
223 204047, 265271, 344857, 448321, 582821, 757693, 985003, 1280519,
224 1664681, 2164111, 2813353, 3657361, 4754591, 6180989, 8035301,
225 10445899, 13579681, 17653589, 22949669, 29834603, 38784989,
226 50420551, 65546729, 85210757, 110774011, 144006217, 187208107,
227 243370577, 316381771, 411296309, 534685237, 695090819, 903618083,
228 1174703521, 1527114613, 1837299131, 2147483647
232 for (i = *prime_offset; i < countof (primes); i++)
233 if (primes[i] >= size)
235 /* Set the offset to the next prime. That is safe because,
236 next time we are called, it will be with a larger SIZE,
237 which means we could never return the same prime anyway.
238 (If that is not the case, the caller can simply reset
240 *prime_offset = i + 1;
247 static int cmp_pointer (const void *, const void *);
249 /* Create a hash table with hash function HASH_FUNCTION and test
250 function TEST_FUNCTION. The table is empty (its count is 0), but
251 pre-allocated to store at least ITEMS items.
253 ITEMS is the number of items that the table can accept without
254 needing to resize. It is useful when creating a table that is to
255 be immediately filled with a known number of items. In that case,
256 the regrows are a waste of time, and specifying ITEMS correctly
257 will avoid them altogether.
259 Note that hash tables grow dynamically regardless of ITEMS. The
260 only use of ITEMS is to preallocate the table and avoid unnecessary
261 dynamic regrows. Don't bother making ITEMS prime because it's not
262 used as size unchanged. To start with a small table that grows as
263 needed, simply specify zero ITEMS.
265 If hash and test callbacks are not specified, identity mapping is
266 assumed, i.e. pointer values are used for key comparison. (Common
267 Lisp calls such tables EQ hash tables, and Java calls them
268 IdentityHashMaps.) If your keys require different comparison,
269 specify hash and test functions. For easy use of C strings as hash
270 keys, you can use the convenience functions make_string_hash_table
271 and make_nocase_string_hash_table. */
274 hash_table_new (int items,
275 unsigned long (*hash_function) (const void *),
276 int (*test_function) (const void *, const void *))
279 struct hash_table *ht = xnew (struct hash_table);
281 ht->hash_function = hash_function ? hash_function : hash_pointer;
282 ht->test_function = test_function ? test_function : cmp_pointer;
284 /* If the size of struct hash_table ever becomes a concern, this
285 field can go. (Wget doesn't create many hashes.) */
286 ht->prime_offset = 0;
288 /* Calculate the size that ensures that the table will store at
289 least ITEMS keys without the need to resize. */
290 size = 1 + items / HASH_MAX_FULLNESS;
291 size = prime_size (size, &ht->prime_offset);
293 ht->resize_threshold = size * HASH_MAX_FULLNESS;
294 /*assert (ht->resize_threshold >= items);*/
296 ht->cells = xnew_array (struct cell, ht->size);
298 /* Mark cells as empty. We use 0xff rather than 0 to mark empty
299 keys because it allows us to use NULL/0 as keys. */
300 memset (ht->cells, INVALID_PTR_CHAR, size * sizeof (struct cell));
307 /* Free the data associated with hash table HT. */
310 hash_table_destroy (struct hash_table *ht)
316 /* The heart of most functions in this file -- find the cell whose
317 KEY is equal to key, using linear probing. Returns the cell
318 that matches KEY, or the first empty cell if none matches. */
320 static inline struct cell *
321 find_cell (const struct hash_table *ht, const void *key)
323 struct cell *cells = ht->cells;
325 struct cell *c = cells + HASH_POSITION (key, ht->hash_function, size);
326 testfun_t equals = ht->test_function;
328 FOREACH_OCCUPIED_ADJACENT (c, cells, size)
329 if (equals (key, c->key))
334 /* Get the value that corresponds to the key KEY in the hash table HT.
335 If no value is found, return NULL. Note that NULL is a legal value
336 for value; if you are storing NULLs in your hash table, you can use
337 hash_table_contains to be sure that a (possibly NULL) value exists
338 in the table. Or, you can use hash_table_get_pair instead of this
342 hash_table_get (const struct hash_table *ht, const void *key)
344 struct cell *c = find_cell (ht, key);
345 if (CELL_OCCUPIED (c))
351 /* Like hash_table_get, but writes out the pointers to both key and
352 value. Returns non-zero on success. */
355 hash_table_get_pair (const struct hash_table *ht, const void *lookup_key,
356 void *orig_key, void *value)
358 struct cell *c = find_cell (ht, lookup_key);
359 if (CELL_OCCUPIED (c))
362 *(void **)orig_key = c->key;
364 *(void **)value = c->value;
371 /* Return 1 if HT contains KEY, 0 otherwise. */
374 hash_table_contains (const struct hash_table *ht, const void *key)
376 struct cell *c = find_cell (ht, key);
377 return CELL_OCCUPIED (c);
380 /* Grow hash table HT as necessary, and rehash all the key-value
384 grow_hash_table (struct hash_table *ht)
386 hashfun_t hasher = ht->hash_function;
387 struct cell *old_cells = ht->cells;
388 struct cell *old_end = ht->cells + ht->size;
389 struct cell *c, *cells;
392 newsize = prime_size (ht->size * HASH_RESIZE_FACTOR, &ht->prime_offset);
394 printf ("growing from %d to %d; fullness %.2f%% to %.2f%%\n",
396 100.0 * ht->count / ht->size,
397 100.0 * ht->count / newsize);
401 ht->resize_threshold = newsize * HASH_MAX_FULLNESS;
403 cells = xnew_array (struct cell, newsize);
404 memset (cells, INVALID_PTR_CHAR, newsize * sizeof (struct cell));
407 for (c = old_cells; c < old_end; c++)
408 if (CELL_OCCUPIED (c))
411 /* We don't need to test for uniqueness of keys because they
412 come from the hash table and are therefore known to be
414 new_c = cells + HASH_POSITION (c->key, hasher, newsize);
415 FOREACH_OCCUPIED_ADJACENT (new_c, cells, newsize)
423 /* Put VALUE in the hash table HT under the key KEY. This regrows the
424 table if necessary. */
427 hash_table_put (struct hash_table *ht, const void *key, void *value)
429 struct cell *c = find_cell (ht, key);
430 if (CELL_OCCUPIED (c))
432 /* update existing item */
433 c->key = (void *)key; /* const? */
438 /* If adding the item would make the table exceed max. fullness,
439 grow the table first. */
440 if (ht->count >= ht->resize_threshold)
442 grow_hash_table (ht);
443 c = find_cell (ht, key);
448 c->key = (void *)key; /* const? */
452 /* Remove KEY->value mapping from HT. Return 0 if there was no such
453 entry; return 1 if an entry was removed. */
456 hash_table_remove (struct hash_table *ht, const void *key)
458 struct cell *c = find_cell (ht, key);
459 if (!CELL_OCCUPIED (c))
464 struct cell *cells = ht->cells;
465 hashfun_t hasher = ht->hash_function;
470 /* Rehash all the entries following C. The alternative
471 approach is to mark the entry as deleted, i.e. create a
472 "tombstone". That speeds up removal, but leaves a lot of
473 garbage and slows down hash_table_get and hash_table_put. */
475 c = NEXT_CELL (c, cells, size);
476 FOREACH_OCCUPIED_ADJACENT (c, cells, size)
478 const void *key2 = c->key;
481 /* Find the new location for the key. */
482 c_new = cells + HASH_POSITION (key2, hasher, size);
483 FOREACH_OCCUPIED_ADJACENT (c_new, cells, size)
484 if (key2 == c_new->key)
485 /* The cell C (key2) is already where we want it (in
486 C_NEW's "chain" of keys.) */
499 /* Clear HT of all entries. After calling this function, the count
500 and the fullness of the hash table will be zero. The size will
504 hash_table_clear (struct hash_table *ht)
506 memset (ht->cells, INVALID_PTR_CHAR, ht->size * sizeof (struct cell));
510 /* Call FN for each entry in HT. FN is called with three arguments:
511 the key, the value, and ARG. When FN returns a non-zero value, the
514 It is undefined what happens if you add or remove entries in the
515 hash table while hash_table_for_each is running. The exception is
516 the entry you're currently mapping over; you may call
517 hash_table_put or hash_table_remove on that entry's key. That is
518 also the reason why this function cannot be implemented in terms of
519 hash_table_iterate. */
522 hash_table_for_each (struct hash_table *ht,
523 int (*fn) (void *, void *, void *), void *arg)
525 struct cell *c = ht->cells;
526 struct cell *end = ht->cells + ht->size;
529 if (CELL_OCCUPIED (c))
534 if (fn (key, c->value, arg))
536 /* hash_table_remove might have moved the adjacent cells. */
537 if (c->key != key && CELL_OCCUPIED (c))
542 /* Initiate iteration over HT. Entries are obtained with
543 hash_table_iter_next, a typical iteration loop looking like this:
545 hash_table_iterator iter;
546 for (hash_table_iterate (ht, &iter); hash_table_iter_next (&iter); )
547 ... do something with iter.key and iter.value ...
549 The iterator does not need to be deallocated after use. The hash
550 table must not be modified while being iterated over. */
553 hash_table_iterate (struct hash_table *ht, hash_table_iterator *iter)
555 iter->pos = ht->cells;
556 iter->end = ht->cells + ht->size;
559 /* Get the next hash table entry. ITER is an iterator object
560 initialized using hash_table_iterate. While there are more
561 entries, the key and value pointers are stored to ITER->key and
562 ITER->value respectively and 1 is returned. When there are no more
563 entries, 0 is returned.
565 If the hash table is modified between calls to this function, the
566 result is undefined. */
569 hash_table_iter_next (hash_table_iterator *iter)
571 struct cell *c = iter->pos;
572 struct cell *end = iter->end;
574 if (CELL_OCCUPIED (c))
577 iter->value = c->value;
584 /* Return the number of elements in the hash table. This is not the
585 same as the physical size of the hash table, which is always
586 greater than the number of elements. */
589 hash_table_count (const struct hash_table *ht)
594 /* Functions from this point onward are meant for convenience and
595 don't strictly belong to this file. However, this is as good a
596 place for them as any. */
598 /* Guidelines for creating custom hash and test functions:
600 - The test function returns non-zero for keys that are considered
601 "equal", zero otherwise.
603 - The hash function returns a number that represents the
604 "distinctness" of the object. In more precise terms, it means
605 that for any two objects that test "equal" under the test
606 function, the hash function MUST produce the same result.
608 This does not mean that all different objects must produce
609 different values (that would be "perfect" hashing), only that
610 non-distinct objects must produce the same values! For instance,
611 a hash function that returns 0 for any given object is a
612 perfectly valid (albeit extremely bad) hash function. A hash
613 function that hashes a string by adding up all its characters is
614 another example of a valid (but still quite bad) hash function.
616 It is not hard to make hash and test functions agree about
617 equality. For example, if the test function compares strings
618 case-insensitively, the hash function can lower-case the
619 characters when calculating the hash value. That ensures that
620 two strings differing only in case will hash the same.
622 - To prevent performance degradation, choose a hash function with
623 as good "spreading" as possible. A good hash function will use
624 all the bits of the input when calculating the hash, and will
625 react to even small changes in input with a completely different
626 output. But don't make the hash function itself overly slow,
627 because you'll be incurring a non-negligible overhead to all hash
631 * Support for hash tables whose keys are strings.
635 /* Base 31 hash function. Taken from Gnome's glib, modified to use
638 We used to use the popular hash function from the Dragon Book, but
639 this one seems to perform much better, both by being faster and by
640 generating less collisions. */
643 hash_string (const void *key)
649 for (p += 1; *p != '\0'; p++)
650 h = (h << 5) - h + *p;
655 /* Frontend for strcmp usable for hash tables. */
658 cmp_string (const void *s1, const void *s2)
660 return !strcmp ((const char *)s1, (const char *)s2);
663 /* Return a hash table of preallocated to store at least ITEMS items
664 suitable to use strings as keys. */
667 make_string_hash_table (int items)
669 return hash_table_new (items, hash_string, cmp_string);
673 * Support for hash tables whose keys are strings, but which are
674 * compared case-insensitively.
678 /* Like hash_string, but produce the same hash regardless of the case. */
681 hash_string_nocase (const void *key)
684 unsigned int h = TOLOWER (*p);
687 for (p += 1; *p != '\0'; p++)
688 h = (h << 5) - h + TOLOWER (*p);
693 /* Like string_cmp, but doing case-insensitive compareison. */
696 string_cmp_nocase (const void *s1, const void *s2)
698 return !strcasecmp ((const char *)s1, (const char *)s2);
701 /* Like make_string_hash_table, but uses string_hash_nocase and
702 string_cmp_nocase. */
705 make_nocase_string_hash_table (int items)
707 return hash_table_new (items, hash_string_nocase, string_cmp_nocase);
710 /* Hashing of numeric values, such as pointers and integers.
712 This implementation is the Robert Jenkins' 32 bit Mix Function,
713 with a simple adaptation for 64-bit values. According to Jenkins
714 it should offer excellent spreading of values. Unlike the popular
715 Knuth's multiplication hash, this function doesn't need to know the
716 hash table size to work. */
719 hash_pointer (const void *ptr)
721 uintptr_t key = (uintptr_t) ptr;
730 #if SIZEOF_VOID_P > 4
740 return (unsigned long) key;
744 cmp_pointer (const void *ptr1, const void *ptr2)
755 print_hash (struct hash_table *sht)
757 hash_table_iterator iter;
760 for (hash_table_iterate (sht, &iter); hash_table_iter_next (&iter);
762 printf ("%s: %s\n", iter.key, iter.value);
763 assert (count == sht->count);
769 struct hash_table *ht = make_string_hash_table (0);
771 while ((fgets (line, sizeof (line), stdin)))
773 int len = strlen (line);
777 if (!hash_table_contains (ht, line))
778 hash_table_put (ht, strdup (line), "here I am!");
783 if (hash_table_get_pair (ht, line, &line_copy, NULL))
785 hash_table_remove (ht, line);
795 printf ("%d %d\n", ht->count, ht->size);