/* Hash tables. Copyright (C) 2000-2011, 2015, 2018-2021 Free Software Foundation, Inc. This file is part of GNU Wget. GNU Wget is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. GNU Wget is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Wget. If not, see . Additional permission under GNU GPL version 3 section 7 If you modify this program, or any covered work, by linking or combining it with the OpenSSL project's OpenSSL library (or a modified version of that library), containing parts covered by the terms of the OpenSSL or SSLeay licenses, the Free Software Foundation grants you additional permission to convey the resulting work. Corresponding Source for a non-source form of such a combination shall include the source code for the parts of OpenSSL used as well as that of the covered work. */ /* With -DSTANDALONE, this file can be compiled outside Wget source tree. To test, also use -DTEST. */ #ifndef STANDALONE # include "wget.h" #endif #include #include #include #include #include #ifndef STANDALONE /* Get Wget's utility headers. */ # include "utils.h" #else /* Make do without them. */ # define xnew(type) (xmalloc (sizeof (type))) # define xnew0(type) (xcalloc (1, sizeof (type))) # define xnew_array(type, len) (xmalloc ((len) * sizeof (type))) # define xfree(p) do { free ((void *) (p)); p = NULL; } while (0) # ifndef countof # define countof(x) (sizeof (x) / sizeof ((x)[0])) # endif # include # define c_tolower(x) tolower ((unsigned char) (x)) # include #endif #include "hash.h" /* INTERFACE: Hash tables are a technique used to implement mapping between objects with near-constant-time access and storage. The table associates keys to values, and a value can be very quickly retrieved by providing the key. Fast lookup tables are typically implemented as hash tables. The entry points are hash_table_new -- creates the table. hash_table_destroy -- destroys the table. hash_table_put -- establishes or updates key->value mapping. hash_table_get -- retrieves value of key. hash_table_get_pair -- get key/value pair for key. hash_table_contains -- test whether the table contains key. hash_table_remove -- remove key->value mapping for given key. hash_table_for_each -- call function for each table entry. hash_table_iterate -- iterate over entries in hash table. hash_table_iter_next -- return next element during iteration. hash_table_clear -- clear hash table contents. hash_table_count -- return the number of entries in the table. The hash table grows internally as new entries are added and is not limited in size, except by available memory. The table doubles with each resize, which ensures that the amortized time per operation remains constant. If not instructed otherwise, tables created by hash_table_new consider the keys to be equal if their pointer values are the same. You can use make_string_hash_table to create tables whose keys are considered equal if their string contents are the same. In the general case, the criterion of equality used to compare keys is specified at table creation time with two callback functions, "hash" and "test". The hash function transforms the key into an arbitrary number that must be the same for two equal keys. The test function accepts two keys and returns non-zero if they are to be considered equal. Note that neither keys nor values are copied when inserted into the hash table, so they must exist for the lifetime of the table. This means that e.g. the use of static strings is OK, but objects with a shorter life-time probably need to be copied (with strdup() or the like in the case of strings) before being inserted. */ /* IMPLEMENTATION: The hash table is implemented as an open-addressed table with linear probing collision resolution. The above means that all the cells (each cell containing a key and a value pointer) are stored in a contiguous array. Array position of each cell is determined by the hash value of its key and the size of the table: location := hash(key) % size. If two different keys end up on the same position (collide), the one that came second is stored in the first unoccupied cell that follows it. This collision resolution technique is called "linear probing". There are more advanced collision resolution methods (quadratic probing, double hashing), but we don't use them because they incur more non-sequential access to the array, which results in worse CPU cache behavior. Linear probing works well as long as the count/size ratio (fullness) is kept below 75%. We make sure to grow and rehash the table whenever this threshold is exceeded. Collisions complicate deletion because simply clearing a cell followed by previously collided entries would cause those neighbors to not be picked up by find_cell later. One solution is to leave a "tombstone" marker instead of clearing the cell, and another is to recalculate the positions of adjacent cells. We take the latter approach because it results in less bookkeeping garbage and faster retrieval at the (slight) expense of deletion. */ /* Maximum allowed fullness: when hash table's fullness exceeds this value, the table is resized. */ #define HASH_MAX_FULLNESS 0.75 /* The hash table size is multiplied by this factor (and then rounded to the next prime) with each resize. This guarantees infrequent resizes. */ #define HASH_RESIZE_FACTOR 2 struct cell { void *key; void *value; }; typedef unsigned long (*hashfun_t) (const void *); typedef int (*testfun_t) (const void *, const void *); struct hash_table { hashfun_t hash_function; testfun_t test_function; struct cell *cells; /* contiguous array of cells. */ int size; /* size of the array. */ int count; /* number of occupied entries. */ int resize_threshold; /* after size exceeds this number of entries, resize the table. */ int prime_offset; /* the offset of the current prime in the prime table. */ }; /* We use the all-bits-set constant (INVALID_PTR) marker to mean that a cell is empty. It is unaligned and therefore illegal as a pointer. INVALID_PTR_CHAR (0xff) is the single-character constant used to initialize the entire cells array as empty. The all-bits-set value is a better choice than NULL because it allows the use of NULL/0 keys. Since the keys are either integers or pointers, the only key that cannot be used is the integer value -1. This is acceptable because it still allows the use of nonnegative integer keys. */ #define INVALID_PTR ((void *) ~(uintptr_t) 0) #ifndef UCHAR_MAX # define UCHAR_MAX 0xff #endif #define INVALID_PTR_CHAR UCHAR_MAX /* Whether the cell C is occupied (non-empty). */ #define CELL_OCCUPIED(c) ((c)->key != INVALID_PTR) /* Clear the cell C, i.e. mark it as empty (unoccupied). */ #define CLEAR_CELL(c) ((c)->key = INVALID_PTR) /* "Next" cell is the cell following C, but wrapping back to CELLS when C would reach CELLS+SIZE. */ #define NEXT_CELL(c, cells, size) (c != cells + (size - 1) ? c + 1 : cells) /* Loop over occupied cells starting at C, terminating the loop when an empty cell is encountered. */ #define FOREACH_OCCUPIED_ADJACENT(c, cells, size) \ for (; CELL_OCCUPIED (c); c = NEXT_CELL (c, cells, size)) /* Return the position of KEY in hash table SIZE large, hash function being HASHFUN. */ #define HASH_POSITION(key, hashfun, size) ((hashfun) (key) % size) /* Find a prime near, but greater than or equal to SIZE. The primes are looked up from a table with a selection of primes convenient for this purpose. PRIME_OFFSET is a minor optimization: it specifies start position for the search for the large enough prime. The final offset is stored in the same variable. That way the list of primes does not have to be scanned from the beginning each time around. */ static int prime_size (int size, int *prime_offset) { static const int primes[] = { 13, 19, 29, 41, 59, 79, 107, 149, 197, 263, 347, 457, 599, 787, 1031, 1361, 1777, 2333, 3037, 3967, 5167, 6719, 8737, 11369, 14783, 19219, 24989, 32491, 42257, 54941, 71429, 92861, 120721, 156941, 204047, 265271, 344857, 448321, 582821, 757693, 985003, 1280519, 1664681, 2164111, 2813353, 3657361, 4754591, 6180989, 8035301, 10445899, 13579681, 17653589, 22949669, 29834603, 38784989, 50420551, 65546729, 85210757, 110774011, 144006217, 187208107, 243370577, 316381771, 411296309, 534685237, 695090819, 903618083, 1174703521, 1527114613, 1837299131, 2147483647 }; size_t i; for (i = *prime_offset; i < countof (primes); i++) if (primes[i] >= size) { /* Set the offset to the next prime. That is safe because, next time we are called, it will be with a larger SIZE, which means we could never return the same prime anyway. (If that is not the case, the caller can simply reset *prime_offset.) */ *prime_offset = i + 1; return primes[i]; } abort (); } static int cmp_pointer (const void *, const void *); /* Create a hash table with hash function HASH_FUNCTION and test function TEST_FUNCTION. The table is empty (its count is 0), but pre-allocated to store at least ITEMS items. ITEMS is the number of items that the table can accept without needing to resize. It is useful when creating a table that is to be immediately filled with a known number of items. In that case, the regrows are a waste of time, and specifying ITEMS correctly will avoid them altogether. Note that hash tables grow dynamically regardless of ITEMS. The only use of ITEMS is to preallocate the table and avoid unnecessary dynamic regrows. Don't bother making ITEMS prime because it's not used as size unchanged. To start with a small table that grows as needed, simply specify zero ITEMS. If hash and test callbacks are not specified, identity mapping is assumed, i.e. pointer values are used for key comparison. (Common Lisp calls such tables EQ hash tables, and Java calls them IdentityHashMaps.) If your keys require different comparison, specify hash and test functions. For easy use of C strings as hash keys, you can use the convenience functions make_string_hash_table and make_nocase_string_hash_table. */ struct hash_table * hash_table_new (int items, unsigned long (*hash_function) (const void *), int (*test_function) (const void *, const void *)) { int size; struct hash_table *ht = xnew (struct hash_table); ht->hash_function = hash_function ? hash_function : hash_pointer; ht->test_function = test_function ? test_function : cmp_pointer; /* If the size of struct hash_table ever becomes a concern, this field can go. (Wget doesn't create many hashes.) */ ht->prime_offset = 0; /* Calculate the size that ensures that the table will store at least ITEMS keys without the need to resize. */ size = (int) (1 + items / HASH_MAX_FULLNESS); size = prime_size (size, &ht->prime_offset); ht->size = size; ht->resize_threshold = (int) (size * HASH_MAX_FULLNESS); /*assert (ht->resize_threshold >= items);*/ ht->cells = xnew_array (struct cell, ht->size); /* Mark cells as empty. We use 0xff rather than 0 to mark empty keys because it allows us to use NULL/0 as keys. */ memset (ht->cells, INVALID_PTR_CHAR, size * sizeof (struct cell)); ht->count = 0; return ht; } /* Free the data associated with hash table HT. */ void hash_table_destroy (struct hash_table *ht) { xfree (ht->cells); xfree (ht); } /* The heart of most functions in this file -- find the cell whose KEY is equal to key, using linear probing. Returns the cell that matches KEY, or the first empty cell if none matches. */ static inline struct cell * find_cell (const struct hash_table *ht, const void *key) { struct cell *cells = ht->cells; int size = ht->size; struct cell *c = cells + HASH_POSITION (key, ht->hash_function, size); testfun_t equals = ht->test_function; FOREACH_OCCUPIED_ADJACENT (c, cells, size) if (equals (key, c->key)) break; return c; } /* Get the value that corresponds to the key KEY in the hash table HT. If no value is found, return NULL. Note that NULL is a legal value for value; if you are storing NULLs in your hash table, you can use hash_table_contains to be sure that a (possibly NULL) value exists in the table. Or, you can use hash_table_get_pair instead of this function. */ void * hash_table_get (const struct hash_table *ht, const void *key) { struct cell *c = find_cell (ht, key); if (CELL_OCCUPIED (c)) return c->value; else return NULL; } /* Like hash_table_get, but writes out the pointers to both key and value. Returns non-zero on success. */ int hash_table_get_pair (const struct hash_table *ht, const void *lookup_key, void *orig_key, void *value) { struct cell *c = find_cell (ht, lookup_key); if (CELL_OCCUPIED (c)) { if (orig_key) *(void **)orig_key = c->key; if (value) *(void **)value = c->value; return 1; } else return 0; } /* Return 1 if HT contains KEY, 0 otherwise. */ int hash_table_contains (const struct hash_table *ht, const void *key) { struct cell *c = find_cell (ht, key); return CELL_OCCUPIED (c); } /* Grow hash table HT as necessary, and rehash all the key-value mappings. */ static void grow_hash_table (struct hash_table *ht) { hashfun_t hasher = ht->hash_function; struct cell *old_cells = ht->cells; struct cell *old_end = ht->cells + ht->size; struct cell *c, *cells; int newsize; newsize = prime_size (ht->size * HASH_RESIZE_FACTOR, &ht->prime_offset); #if 0 printf ("growing from %d to %d; fullness %.2f%% to %.2f%%\n", ht->size, newsize, 100.0 * ht->count / ht->size, 100.0 * ht->count / newsize); #endif ht->size = newsize; ht->resize_threshold = (int) (newsize * HASH_MAX_FULLNESS); cells = xnew_array (struct cell, newsize); memset (cells, INVALID_PTR_CHAR, newsize * sizeof (struct cell)); ht->cells = cells; for (c = old_cells; c < old_end; c++) if (CELL_OCCUPIED (c)) { struct cell *new_c; /* We don't need to test for uniqueness of keys because they come from the hash table and are therefore known to be unique. */ new_c = cells + HASH_POSITION (c->key, hasher, newsize); FOREACH_OCCUPIED_ADJACENT (new_c, cells, newsize) ; *new_c = *c; } xfree (old_cells); } /* Put VALUE in the hash table HT under the key KEY. This regrows the table if necessary. */ void hash_table_put (struct hash_table *ht, const void *key, const void *value) { struct cell *c = find_cell (ht, key); if (CELL_OCCUPIED (c)) { /* update existing item */ c->key = (void *)key; /* const? */ c->value = (void *)value; return; } /* If adding the item would make the table exceed max. fullness, grow the table first. */ if (ht->count >= ht->resize_threshold) { grow_hash_table (ht); c = find_cell (ht, key); } /* add new item */ ++ht->count; c->key = (void *)key; /* const? */ c->value = (void *)value; } /* Remove KEY->value mapping from HT. Return 0 if there was no such entry; return 1 if an entry was removed. */ int hash_table_remove (struct hash_table *ht, const void *key) { struct cell *c = find_cell (ht, key); if (!CELL_OCCUPIED (c)) return 0; else { int size = ht->size; struct cell *cells = ht->cells; hashfun_t hasher = ht->hash_function; CLEAR_CELL (c); --ht->count; /* Rehash all the entries following C. The alternative approach is to mark the entry as deleted, i.e. create a "tombstone". That speeds up removal, but leaves a lot of garbage and slows down hash_table_get and hash_table_put. */ c = NEXT_CELL (c, cells, size); FOREACH_OCCUPIED_ADJACENT (c, cells, size) { const void *key2 = c->key; struct cell *c_new; /* Find the new location for the key. */ c_new = cells + HASH_POSITION (key2, hasher, size); FOREACH_OCCUPIED_ADJACENT (c_new, cells, size) if (key2 == c_new->key) /* The cell C (key2) is already where we want it (in C_NEW's "chain" of keys.) */ goto next_rehash; *c_new = *c; CLEAR_CELL (c); next_rehash: ; } return 1; } } /* Clear HT of all entries. After calling this function, the count and the fullness of the hash table will be zero. The size will remain unchanged. */ void hash_table_clear (struct hash_table *ht) { memset (ht->cells, INVALID_PTR_CHAR, ht->size * sizeof (struct cell)); ht->count = 0; } /* Call FN for each entry in HT. FN is called with three arguments: the key, the value, and ARG. When FN returns a non-zero value, the mapping stops. It is undefined what happens if you add or remove entries in the hash table while hash_table_for_each is running. The exception is the entry you're currently mapping over; you may call hash_table_put or hash_table_remove on that entry's key. That is also the reason why this function cannot be implemented in terms of hash_table_iterate. */ void hash_table_for_each (struct hash_table *ht, int (*fn) (void *, void *, void *), void *arg) { struct cell *c = ht->cells; struct cell *end = ht->cells + ht->size; for (; c < end; c++) if (CELL_OCCUPIED (c)) { void *key; repeat: key = c->key; if (fn (key, c->value, arg)) return; /* hash_table_remove might have moved the adjacent cells. */ if (c->key != key && CELL_OCCUPIED (c)) goto repeat; } } /* Initiate iteration over HT. Entries are obtained with hash_table_iter_next, a typical iteration loop looking like this: hash_table_iterator iter; for (hash_table_iterate (ht, &iter); hash_table_iter_next (&iter); ) ... do something with iter.key and iter.value ... The iterator does not need to be deallocated after use. The hash table must not be modified while being iterated over. */ void hash_table_iterate (struct hash_table *ht, hash_table_iterator *iter) { iter->pos = ht->cells; iter->end = ht->cells + ht->size; } /* Get the next hash table entry. ITER is an iterator object initialized using hash_table_iterate. While there are more entries, the key and value pointers are stored to ITER->key and ITER->value respectively and 1 is returned. When there are no more entries, 0 is returned. If the hash table is modified between calls to this function, the result is undefined. */ int hash_table_iter_next (hash_table_iterator *iter) { struct cell *c = iter->pos; struct cell *end = iter->end; for (; c < end; c++) if (CELL_OCCUPIED (c)) { iter->key = c->key; iter->value = c->value; iter->pos = c + 1; return 1; } return 0; } /* Return the number of elements in the hash table. This is not the same as the physical size of the hash table, which is always greater than the number of elements. */ int hash_table_count (const struct hash_table *ht) { return ht->count; } /* Functions from this point onward are meant for convenience and don't strictly belong to this file. However, this is as good a place for them as any. */ /* Guidelines for creating custom hash and test functions: - The test function returns non-zero for keys that are considered "equal", zero otherwise. - The hash function returns a number that represents the "distinctness" of the object. In more precise terms, it means that for any two objects that test "equal" under the test function, the hash function MUST produce the same result. This does not mean that all different objects must produce different values (that would be "perfect" hashing), only that non-distinct objects must produce the same values! For instance, a hash function that returns 0 for any given object is a perfectly valid (albeit extremely bad) hash function. A hash function that hashes a string by adding up all its characters is another example of a valid (but still quite bad) hash function. It is not hard to make hash and test functions agree about equality. For example, if the test function compares strings case-insensitively, the hash function can lower-case the characters when calculating the hash value. That ensures that two strings differing only in case will hash the same. - To prevent performance degradation, choose a hash function with as good "spreading" as possible. A good hash function will use all the bits of the input when calculating the hash, and will react to even small changes in input with a completely different output. But don't make the hash function itself overly slow, because you'll be incurring a non-negligible overhead to all hash table operations. */ /* * Support for hash tables whose keys are strings. * */ /* Base 31 hash function. Taken from Gnome's glib, modified to use standard C types. We used to use the popular hash function from the Dragon Book, but this one seems to perform much better, both by being faster and by generating less collisions. */ #ifdef __clang__ __attribute__((no_sanitize("integer"))) #endif static unsigned long hash_string (const void *key) { const char *p = key; unsigned int h = *p; if (h) for (p += 1; *p != '\0'; p++) h = (h << 5) - h + *p; return h; } /* Frontend for strcmp usable for hash tables. */ static int cmp_string (const void *s1, const void *s2) { return !strcmp ((const char *)s1, (const char *)s2); } /* Return a hash table of preallocated to store at least ITEMS items suitable to use strings as keys. */ struct hash_table * make_string_hash_table (int items) { return hash_table_new (items, hash_string, cmp_string); } /* * Support for hash tables whose keys are strings, but which are * compared case-insensitively. * */ /* Like hash_string, but produce the same hash regardless of the case. */ #ifdef __clang__ __attribute__((no_sanitize("integer"))) #endif static unsigned long hash_string_nocase (const void *key) { const char *p = key; unsigned int h = c_tolower (*p); if (h) for (p += 1; *p != '\0'; p++) h = (h << 5) - h + c_tolower (*p); return h; } /* Like string_cmp, but doing case-insensitive comparison. */ static int string_cmp_nocase (const void *s1, const void *s2) { return !strcasecmp ((const char *)s1, (const char *)s2); } /* Like make_string_hash_table, but uses string_hash_nocase and string_cmp_nocase. */ struct hash_table * make_nocase_string_hash_table (int items) { return hash_table_new (items, hash_string_nocase, string_cmp_nocase); } /* Hashing of numeric values, such as pointers and integers. This implementation is the Robert Jenkins' 32 bit Mix Function, with a simple adaptation for 64-bit values. According to Jenkins it should offer excellent spreading of values. Unlike the popular Knuth's multiplication hash, this function doesn't need to know the hash table size to work. */ #ifdef __clang__ __attribute__((no_sanitize("integer"))) #endif unsigned long hash_pointer (const void *ptr) { uintptr_t key = (uintptr_t) ptr; key += (key << 12); key ^= (key >> 22); key += (key << 4); key ^= (key >> 9); key += (key << 10); key ^= (key >> 2); key += (key << 7); key ^= (key >> 12); #if SIZEOF_VOID_P > 4 key += (key << 44); key ^= (key >> 54); key += (key << 36); key ^= (key >> 41); key += (key << 42); key ^= (key >> 34); key += (key << 39); key ^= (key >> 44); #endif return (unsigned long) key; } static int cmp_pointer (const void *ptr1, const void *ptr2) { return ptr1 == ptr2; } #ifdef TEST #include #include void print_hash (struct hash_table *sht) { hash_table_iterator iter; int count = 0; for (hash_table_iterate (sht, &iter); hash_table_iter_next (&iter); ++count) printf ("%s: %s\n", iter.key, iter.value); assert (count == sht->count); } int main (void) { struct hash_table *ht = make_string_hash_table (0); char line[80]; #ifdef ENABLE_NLS /* Set the current locale. */ setlocale (LC_ALL, ""); /* Set the text message domain. */ bindtextdomain ("wget", LOCALEDIR); textdomain ("wget"); #endif /* ENABLE_NLS */ while ((fgets (line, sizeof (line), stdin))) { int len = strlen (line); if (len <= 1) continue; line[--len] = '\0'; if (!hash_table_contains (ht, line)) hash_table_put (ht, strdup (line), "here I am!"); #if 1 if (len % 5 == 0) { char *line_copy; if (hash_table_get_pair (ht, line, &line_copy, NULL)) { hash_table_remove (ht, line); xfree (line_copy); } } #endif } #if 0 print_hash (ht); #endif #if 1 printf ("%d %d\n", ht->count, ht->size); #endif return 0; } #endif /* TEST */