/* Hash tables.
- Copyright (C) 2000 Free Software Foundation, Inc.
+ Copyright (C) 2000, 2001 Free Software Foundation, Inc.
-This file is part of Wget.
+This file is part of GNU Wget.
-This program is free software; you can redistribute it and/or modify
+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 2 of the License, or (at
your option) any later version.
-This program is distributed in the hope that it will be useful,
+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 this program; if not, write to the Free Software
+along with Wget; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
#ifdef HAVE_CONFIG_H
The basics are all covered. hash_table_new creates a hash table,
and hash_table_destroy deletes it. hash_table_put establishes a
mapping between a key and a value. hash_table_get retrieves the
- value that corresponds to a key. hash_table_exists queries whether
- a key is stored in a table at all. hash_table_remove removes a
- mapping that corresponds to a key. hash_table_map allows you to
- map through all the entries in a hash table. hash_table_clear
- clears all the entries from the hash table.
+ value that corresponds to a key. hash_table_contains queries
+ whether a key is stored in a table at all. hash_table_remove
+ removes a mapping that corresponds to a key. hash_table_map allows
+ you to map through all the entries in a hash table.
+ hash_table_clear clears all the entries from the hash table.
The number of mappings in a table is not limited, except by the
amount of memory. As you add new elements to a table, it regrows
The hashing and equality functions are normally provided by the
user. For the special (and frequent) case of hashing strings, you
- can use the pre-canned make_string_hash_table(), which provides the
- string hashing function from the Dragon Book, and a string equality
- wrapper around strcmp().
+ can use the pre-canned make_string_hash_table(), which provides an
+ efficient string hashing function, and a string equality wrapper
+ around strcmp().
When specifying your own hash and test functions, make sure the
following holds true:
distinct value, 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 quite bad) hash
function.
The above stated rule is quite easy to enforce. For example, if
your testing function compares strings case-insensitively, all
your function needs to do is lower-case the string characters
before calculating a hash. That way you have easily guaranteed
- that changes in case will not result in a different hash.
+ that case differences will not result in a different hash.
- (optional) Choose the hash function to get as good "spreading" as
possible. A good hash function will react to even a small change
Collisions make deletion tricky because finding collisions again
relies on new empty spots not being created. That's why
- hash_table_remove only marks the spot as deleted rather than really
- making it empty. */
+ hash_table_remove is careful to rehash the mappings that follow the
+ deleted one. */
struct mapping {
void *key;
};
struct hash_table {
- unsigned long (*hash_function) (const void *);
- int (*test_function) (const void *, const void *);
+ unsigned long (*hash_function) PARAMS ((const void *));
+ int (*test_function) PARAMS ((const void *, const void *));
int size; /* size of the array */
- int fullness; /* number of non-empty fields */
int count; /* number of non-empty, non-deleted
fields. */
+ int resize_threshold; /* after size exceeds this number of
+ entries, resize the table. */
+
struct mapping *mappings;
};
-#define ENTRY_DELETED ((void *)0xdeadbeef)
-#define ENTRY_EMPTY NULL
+#define EMPTY_MAPPING_P(mp) ((mp)->key == NULL)
+#define NEXT_MAPPING(mp, mappings, size) (mp == mappings + (size - 1) \
+ ? mappings : mp + 1)
+
+#define LOOP_NON_EMPTY(mp, mappings, size) \
+ for (; !EMPTY_MAPPING_P (mp); mp = NEXT_MAPPING (mp, mappings, size))
-#define DELETED_ENTRY_P(ptr) ((ptr) == ENTRY_DELETED)
-#define EMPTY_ENTRY_P(ptr) ((ptr) == ENTRY_EMPTY)
+/* #### We might want to multiply with the "golden ratio" here to get
+ better randomness for keys that do not result from a good hash
+ function. This is currently not a problem in Wget because we only
+ use the string hash tables. */
+
+#define HASH_POSITION(ht, key) (ht->hash_function (key) % ht->size)
/* Find a prime near, but greather than or equal to SIZE. */
-int
+static int
prime_size (int size)
{
static const unsigned long primes [] = {
10445899, 13579681, 17653589, 22949669, 29834603, 38784989,
50420551, 65546729, 85210757, 110774011, 144006217, 187208107,
243370577, 316381771, 411296309, 534685237, 695090819, 903618083,
- 1174703521, 1527114613, 1985248999, 2580823717UL, 3355070839UL
+ 1174703521, 1527114613, 1985248999,
+ (unsigned long)0x99d43ea5, (unsigned long)0xc7fa5177
};
int i;
for (i = 0; i < ARRAY_SIZE (primes); i++)
}
/* Create a hash table of INITIAL_SIZE with hash function
- HASH_FUNCTION and test function TEST_FUNCTION. If you wish to
- start out with a "small" table which will be regrown as needed,
- specify 0 as INITIAL_SIZE. */
+ HASH_FUNCTION and test function TEST_FUNCTION. INITIAL_SIZE will
+ be rounded to the next prime, so you don't have to worry about it
+ being a prime number.
+
+ Consequently, if you wish to start out with a "small" table which
+ will be regrown as needed, specify INITIAL_SIZE 0. */
struct hash_table *
hash_table_new (int initial_size,
{
struct hash_table *ht
= (struct hash_table *)xmalloc (sizeof (struct hash_table));
+
ht->hash_function = hash_function;
ht->test_function = test_function;
+
ht->size = prime_size (initial_size);
- ht->fullness = 0;
+ ht->resize_threshold = ht->size * 3 / 4;
+
ht->count = 0;
+
ht->mappings = xmalloc (ht->size * sizeof (struct mapping));
memset (ht->mappings, '\0', ht->size * sizeof (struct mapping));
+
return ht;
}
}
/* The heart of almost all functions in this file -- find the mapping
- whose KEY is equal to key, using a linear probing loop. Returns
- the offset of the mapping in ht->mappings. This should probably be
- declared inline. */
+ whose KEY is equal to key, using linear probing. Returns the
+ mapping that matches KEY, or NULL if none matches. */
-static int
+static inline struct mapping *
find_mapping (struct hash_table *ht, const void *key)
{
struct mapping *mappings = ht->mappings;
int size = ht->size;
- int location = ht->hash_function (key) % size;
- while (1)
- {
- struct mapping *mp = mappings + location;
- void *mp_key = mp->key;
+ struct mapping *mp = mappings + HASH_POSITION (ht, key);
+ int (*equals) PARAMS ((const void *, const void *)) = ht->test_function;
- if (EMPTY_ENTRY_P (mp_key))
- return -1;
- else if (DELETED_ENTRY_P (mp_key)
- || !ht->test_function (key, mp_key))
- {
- if (++location == size)
- location = 0;
- }
- else
- return location;
- }
+ LOOP_NON_EMPTY (mp, mappings, size)
+ if (equals (key, mp->key))
+ return mp;
+ return NULL;
}
/* 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_exists to be sure that a (possibly NULL) value exists in
- the table. Or, you can use hash_table_get_pair instead of this
+ 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 (struct hash_table *ht, const void *key)
{
- int location = find_mapping (ht, key);
- if (location < 0)
- return NULL;
+ struct mapping *mp = find_mapping (ht, key);
+ if (mp)
+ return mp->value;
else
- return ht->mappings[location].value;
+ return NULL;
}
/* Like hash_table_get, but writes out the pointers to both key and
hash_table_get_pair (struct hash_table *ht, const void *lookup_key,
void *orig_key, void *value)
{
- int location = find_mapping (ht, lookup_key);
- if (location < 0)
- return 0;
- else
+ struct mapping *mp = find_mapping (ht, lookup_key);
+
+ if (mp)
{
- struct mapping *mp = ht->mappings + location;
if (orig_key)
*(void **)orig_key = mp->key;
if (value)
*(void **)value = mp->value;
return 1;
}
+ else
+ return 0;
}
-/* Return 1 if KEY exists in HT, 0 otherwise. */
+/* Return 1 if HT contains KEY, 0 otherwise. */
int
-hash_table_exists (struct hash_table *ht, const void *key)
+hash_table_contains (struct hash_table *ht, const void *key)
{
- return find_mapping (ht, key) >= 0;
+ return find_mapping (ht, key) != NULL;
}
-#define MAX(i, j) (((i) >= (j)) ? (i) : (j))
-
/* Grow hash table HT as necessary, and rehash all the key-value
mappings. */
static void
grow_hash_table (struct hash_table *ht)
{
- int i;
struct mapping *old_mappings = ht->mappings;
- int old_count = ht->count; /* for assert() below */
- int old_size = ht->size;
-
- /* To minimize the number of regrowth, we'd like to resize the hash
- table exponentially. Normally, this would be done by doubling
- ht->size (and round it to next prime) on each regrow:
-
- ht->size = prime_size (ht->size * 2);
-
- But it is possible that the table has large fullness because of
- the many deleted entries. If that is the case, we don't want to
- blindly grow the table; we just want to rehash it. For that
- reason, we use ht->count as the relevant parameter. MAX is used
- only because we don't want to actually shrink the table. (But
- maybe that's wrong.) */
-
- int needed_size = prime_size (ht->count * 3);
- ht->size = MAX (old_size, needed_size);
+ struct mapping *old_end = ht->mappings + ht->size;
+ struct mapping *mp, *mappings;
+ int newsize;
+ newsize = prime_size (ht->size * 2);
#if 0
- printf ("growing from %d to %d\n", old_size, ht->size);
+ printf ("growing from %d to %d\n", ht->size, newsize);
#endif
- ht->mappings = xmalloc (ht->size * sizeof (struct mapping));
- memset (ht->mappings, '\0', ht->size * sizeof (struct mapping));
-
- /* Need to reset these two; hash_table_put will reinitialize them. */
- ht->fullness = 0;
- ht->count = 0;
- for (i = 0; i < old_size; i++)
- {
- struct mapping *mp = old_mappings + i;
- void *mp_key = mp->key;
+ ht->size = newsize;
+ ht->resize_threshold = newsize * 3 / 4;
+
+ mappings = xmalloc (ht->size * sizeof (struct mapping));
+ memset (mappings, '\0', ht->size * sizeof (struct mapping));
+ ht->mappings = mappings;
+
+ for (mp = old_mappings; mp < old_end; mp++)
+ if (!EMPTY_MAPPING_P (mp))
+ {
+ struct mapping *new_mp = mappings + HASH_POSITION (ht, mp->key);
+ /* We don't need to call test function and worry about
+ collisions because all the keys come from the hash table
+ and are therefore guaranteed to be unique. */
+ LOOP_NON_EMPTY (new_mp, mappings, newsize)
+ ;
+ *new_mp = *mp;
+ }
- if (!EMPTY_ENTRY_P (mp_key)
- && !DELETED_ENTRY_P (mp_key))
- hash_table_put (ht, mp_key, mp->value);
- }
- assert (ht->count == old_count);
xfree (old_mappings);
}
void
hash_table_put (struct hash_table *ht, const void *key, void *value)
{
- /* Cannot use find_mapping here because we're actually looking for
- an *empty* entry. */
-
struct mapping *mappings = ht->mappings;
int size = ht->size;
- int location = ht->hash_function (key) % size;
- while (1)
- {
- struct mapping *mp = mappings + location;
- void *mp_key = mp->key;
+ int (*equals) PARAMS ((const void *, const void *)) = ht->test_function;
- if (EMPTY_ENTRY_P (mp_key))
- {
- ++ht->fullness;
- ++ht->count;
- just_insert:
- mp->key = (void *)key; /* const? */
- mp->value = value;
- break;
- }
- else if (DELETED_ENTRY_P (mp_key)
- || !ht->test_function (key, mp_key))
- {
- if (++location == size)
- location = 0;
- }
- else /* equal to key and not deleted */
- {
- /* We're replacing an existing entry, so ht->count and
- ht->fullness remain unchanged. */
- goto just_insert;
- }
- }
- if (ht->fullness * 4 > ht->size * 3)
- /* When fullness exceeds 75% of size, regrow the table. */
+ struct mapping *mp = mappings + HASH_POSITION (ht, key);
+
+ LOOP_NON_EMPTY (mp, mappings, size)
+ if (equals (key, mp->key))
+ {
+ mp->key = (void *)key; /* const? */
+ mp->value = value;
+ return;
+ }
+
+ ++ht->count;
+ mp->key = (void *)key; /* const? */
+ mp->value = value;
+
+ if (ht->count > ht->resize_threshold)
+ /* When table is 75% full, regrow it. */
grow_hash_table (ht);
}
-/* Remove KEY from HT. */
+/* Remove a mapping that matches KEY 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)
{
- int location = find_mapping (ht, key);
- if (location < 0)
+ struct mapping *mp = find_mapping (ht, key);
+ if (!mp)
return 0;
else
{
+ int size = ht->size;
struct mapping *mappings = ht->mappings;
- struct mapping *mp = mappings + location;
- /* We don't really remove an entry from the hash table: we just
- mark it as deleted. This is because there may be other
- entries located after this entry whose hash points to a
- location before this entry. (Example: keys A, B and C have
- the same hash. If you were to really *delete* B from the
- table, C could no longer be found.) */
-
- /* Optimization addendum: if the mapping that follows LOCATION
- is already empty, that is a sure sign that nobody depends on
- LOCATION being non-empty. (This is because we're using
- linear probing. This would not be the case with double
- hashing.) In that case, we may safely delete the mapping. */
-
- /* This could be generalized so that the all the non-empty
- locations following LOCATION are simply shifted leftward. It
- would make deletion a bit slower, but it would remove the
- ugly DELETED_ENTRY_P checks from all the rest of the code,
- making the whole thing faster. */
- int location_after = (location + 1) == ht->size ? 0 : location + 1;
- struct mapping *mp_after = mappings + location_after;
-
- if (EMPTY_ENTRY_P (mp_after->key))
- {
- mp->key = ENTRY_EMPTY;
- --ht->fullness;
- }
- else
- mp->key = ENTRY_DELETED;
+ mp->key = NULL;
--ht->count;
+
+ /* Rehash all the entries following MP. The alternative
+ approach is to mark the entry as deleted, i.e. create a
+ "tombstone". That makes remove faster, but leaves a lot of
+ garbage and slows down hash_table_get and hash_table_put. */
+
+ mp = NEXT_MAPPING (mp, mappings, size);
+ LOOP_NON_EMPTY (mp, mappings, size)
+ {
+ const void *key2 = mp->key;
+ struct mapping *mp_new = mappings + HASH_POSITION (ht, key2);
+
+ /* Find the new location for the key. */
+
+ LOOP_NON_EMPTY (mp_new, mappings, size)
+ if (key2 == mp_new->key)
+ /* The mapping MP (key2) is already where we want it (in
+ MP_NEW's "chain" of keys.) */
+ goto next_rehash;
+
+ *mp_new = *mp;
+ mp->key = NULL;
+
+ next_rehash:
+ ;
+ }
return 1;
}
}
hash_table_clear (struct hash_table *ht)
{
memset (ht->mappings, '\0', ht->size * sizeof (struct mapping));
- ht->fullness = 0;
- ht->count = 0;
+ ht->count = 0;
}
/* Map MAPFUN over all the mappings in hash table HT. MAPFUN is
called with three arguments: the key, the value, and the CLOSURE.
- Don't add or remove entries from HT while hash_table_map is being
- called, or strange things may happen. */
+
+ It is undefined what happens if you add or remove entries in the
+ hash table while hash_table_map is running. The exception is the
+ entry you're currently mapping over; you may remove or change that
+ entry. */
void
hash_table_map (struct hash_table *ht,
int (*mapfun) (void *, void *, void *),
void *closure)
{
- struct mapping *mappings = ht->mappings;
- int i;
- for (i = 0; i < ht->size; i++)
- {
- struct mapping *mp = mappings + i;
- void *mp_key = mp->key;
-
- if (!EMPTY_ENTRY_P (mp_key)
- && !DELETED_ENTRY_P (mp_key))
- if (mapfun (mp_key, mp->value, closure))
+ struct mapping *mp = ht->mappings;
+ struct mapping *end = ht->mappings + ht->size;
+
+ for (; mp < end; mp++)
+ if (!EMPTY_MAPPING_P (mp))
+ {
+ void *key;
+ repeat:
+ key = mp->key;
+ if (mapfun (key, mp->value, closure))
return;
- }
+ /* hash_table_remove might have moved the adjacent
+ mappings. */
+ if (mp->key != key && !EMPTY_MAPPING_P (mp))
+ goto repeat;
+ }
}
/* 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 (struct hash_table *ht)
{
return ht->count;
}
\f
-/* Support for hash tables whose keys are strings. */
+/* 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. */
+
+/* ========
+ Support for hash tables whose keys are strings.
+ ======== */
+
+/* 31 bit 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. */
-/* supposedly from the Dragon Book P436. */
unsigned long
-string_hash (const void *sv)
+string_hash (const void *key)
{
- unsigned int h = 0;
- unsigned const char *x = (unsigned const char *) sv;
+ const char *p = key;
+ unsigned int h = *p;
+
+ if (h)
+ for (p += 1; *p != '\0'; p++)
+ h = (h << 5) - h + *p;
+
+ return h;
+}
- while (*x)
- {
- unsigned int g;
- h = (h << 4) + *x++;
- if ((g = h & 0xf0000000) != 0)
- h = (h ^ (g >> 24)) ^ g;
- }
+/* Frontend for strcmp usable for hash tables. */
+
+int
+string_cmp (const void *s1, const void *s2)
+{
+ return !strcmp ((const char *)s1, (const char *)s2);
+}
+
+/* Return a hash table of initial size INITIAL_SIZE suitable to use
+ strings as keys. */
+
+struct hash_table *
+make_string_hash_table (int initial_size)
+{
+ return hash_table_new (initial_size, string_hash, string_cmp);
+}
+/* ========
+ Support for hash tables whose keys are strings, but which are
+ compared case-insensitively.
+ ======== */
+
+/* Like string_hash, but produce the same hash regardless of the case. */
+
+static unsigned long
+string_hash_nocase (const void *key)
+{
+ const char *p = key;
+ unsigned int h = TOLOWER (*p);
+
+ if (h)
+ for (p += 1; *p != '\0'; p++)
+ h = (h << 5) - h + TOLOWER (*p);
+
return h;
}
+/* Like string_cmp, but doing case-insensitive compareison. */
+
+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 initial_size)
+{
+ return hash_table_new (initial_size, string_hash_nocase, string_cmp_nocase);
+}
+
#if 0
/* If I ever need it: hashing of integers. */
return key;
}
#endif
-
-int
-string_cmp (const void *s1, const void *s2)
-{
- return !strcmp ((const char *)s1, (const char *)s2);
-}
-
-/* Return a hash table of initial size INITIAL_SIZE suitable to use
- strings as keys. */
-
-struct hash_table *
-make_string_hash_table (int initial_size)
-{
- return hash_table_new (initial_size, string_hash, string_cmp);
-}
-
\f
#ifdef STANDALONE
if (len <= 1)
continue;
line[--len] = '\0';
- if (!hash_table_exists (ht, line))
+ if (!hash_table_contains (ht, line))
hash_table_put (ht, strdup (line), "here I am!");
#if 1
- if (len % 3)
+ if (len % 5 == 0)
{
char *line_copy;
if (hash_table_get_pair (ht, line, &line_copy, NULL))
print_hash (ht);
#endif
#if 1
- printf ("%d %d %d\n", ht->count, ht->fullness, ht->size);
+ printf ("%d %d\n", ht->count, ht->size);
#endif
return 0;
}
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