mirror of https://github.com/moparisthebest/wget
[svn] Commit various hash table changes:
* hash.c (hash_table_map): Allow deletion and change of the element processed by MAPFUN. (string_hash): Use the function from glib. * hash.c (hash_table_remove): Rewrite to actually clear deleted entries instead of just marking them as deleted. Published in <sxsu23tvdur.fsf@florida.arsdigita.de>.
This commit is contained in:
hniksic
parent
452c0bb9f7
commit
eae28f142d
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@ -1,3 +1,7 @@
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2001-04-12 Hrvoje Niksic <hniksic@arsdigita.com>
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* configure.in: Check for inline.
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2001-04-11 Hrvoje Niksic <hniksic@arsdigita.com>
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* po/zh_TW.Big5.po: New file, submitted by Abel Cheung.
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@ -140,6 +140,7 @@ dnl
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dnl Checks for typedefs, structures, and compiler characteristics.
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dnl
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AC_C_CONST
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AC_C_INLINE
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AC_TYPE_SIZE_T
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AC_TYPE_PID_T
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dnl #### This generates a warning. What do I do to shut it up?
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@ -1,3 +1,19 @@
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2001-04-13 Hrvoje Niksic <hniksic@arsdigita.com>
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* cookies.c (unsigned_string_hash): Use the new code in
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string_hash as reference.
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* hash.c (hash_table_map): Allow deletion and change of the
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element processed by MAPFUN.
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(string_hash): Use the function from glib.
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2001-04-12 Hrvoje Niksic <hniksic@arsdigita.com>
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* config.h.in: Include #undef stub.
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* hash.c (hash_table_remove): Rewrite to actually clear deleted
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entries instead of just marking them as deleted.
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2001-04-12 Hrvoje Niksic <hniksic@arsdigita.com>
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* hash.h: Declare hash_table_get_pair and hash_table_count.
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@ -50,6 +50,9 @@ char *alloca ();
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/* Define to empty if the keyword does not work. */
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#undef const
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/* Define to empty or __inline__ or __inline. */
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#undef inline
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/* Define to `unsigned' if <sys/types.h> doesn't define. */
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#undef size_t
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@ -111,21 +111,15 @@ delete_cookie (struct cookie *cookie)
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case. */
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static unsigned long
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unsigned_string_hash (const void *sv)
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unsigned_string_hash (const void *key)
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{
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unsigned int h = 0;
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unsigned const char *x = (unsigned const char *) sv;
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while (*x)
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{
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unsigned int g;
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unsigned char c = TOLOWER (*x);
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h = (h << 4) + c;
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if ((g = h & 0xf0000000) != 0)
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h = (h ^ (g >> 24)) ^ g;
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++x;
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}
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const char *p = key;
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unsigned int h = TOLOWER (*p);
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if (h)
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for (p += 1; *p != '\0'; p++)
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h = (h << 5) - h + TOLOWER (*p);
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return h;
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}
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279
src/hash.c
279
src/hash.c
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@ -1,5 +1,5 @@
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/* Hash tables.
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Copyright (C) 2000 Free Software Foundation, Inc.
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Copyright (C) 2000, 2001 Free Software Foundation, Inc.
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This file is part of Wget.
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@ -86,13 +86,15 @@ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
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distinct value, only that non-distinct objects must produce the
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same values! For instance, a hash function that returns 0 for
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any given object is a perfectly valid (albeit extremely bad) hash
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function. A hash function that hashes a string by adding up all
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its characters is another example of a valid (but quite bad) hash
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function.
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The above stated rule is quite easy to enforce. For example, if
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your testing function compares strings case-insensitively, all
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your function needs to do is lower-case the string characters
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before calculating a hash. That way you have easily guaranteed
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that changes in case will not result in a different hash.
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that case differences will not result in a different hash.
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- (optional) Choose the hash function to get as good "spreading" as
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possible. A good hash function will react to even a small change
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@ -125,8 +127,8 @@ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
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Collisions make deletion tricky because finding collisions again
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relies on new empty spots not being created. That's why
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hash_table_remove only marks the spot as deleted rather than really
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making it empty. */
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hash_table_remove is careful to rehash the mappings that follow the
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deleted one. */
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struct mapping {
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void *key;
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@ -138,18 +140,20 @@ struct hash_table {
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int (*test_function) (const void *, const void *);
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int size; /* size of the array */
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int fullness; /* number of non-empty fields */
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int count; /* number of non-empty, non-deleted
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fields. */
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struct mapping *mappings;
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};
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#define ENTRY_DELETED ((void *)0xdeadbeef)
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#define ENTRY_EMPTY NULL
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#define EMPTY_MAPPING_P(mp) ((mp)->key == NULL)
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#define NEXT_MAPPING(mp, mappings, size) (mp == mappings + (size - 1) \
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? mappings : mp + 1)
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#define DELETED_ENTRY_P(ptr) ((ptr) == ENTRY_DELETED)
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#define EMPTY_ENTRY_P(ptr) ((ptr) == ENTRY_EMPTY)
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#define LOOP_NON_EMPTY(mp, mappings, size) \
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for (; !EMPTY_MAPPING_P (mp); mp = NEXT_MAPPING (mp, mappings, size))
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#define HASH_POSITION(ht, key) (ht->hash_function (key) % ht->size)
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/* Find a prime near, but greather than or equal to SIZE. */
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@ -190,7 +194,6 @@ hash_table_new (int initial_size,
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ht->hash_function = hash_function;
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ht->test_function = test_function;
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ht->size = prime_size (initial_size);
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ht->fullness = 0;
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ht->count = 0;
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ht->mappings = xmalloc (ht->size * sizeof (struct mapping));
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memset (ht->mappings, '\0', ht->size * sizeof (struct mapping));
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@ -208,31 +211,20 @@ hash_table_destroy (struct hash_table *ht)
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/* The heart of almost all functions in this file -- find the mapping
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whose KEY is equal to key, using a linear probing loop. Returns
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the offset of the mapping in ht->mappings. This should probably be
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declared inline. */
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the offset of the mapping in ht->mappings. */
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static int
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static inline struct mapping *
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find_mapping (struct hash_table *ht, const void *key)
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{
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struct mapping *mappings = ht->mappings;
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int size = ht->size;
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int location = ht->hash_function (key) % size;
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while (1)
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{
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struct mapping *mp = mappings + location;
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void *mp_key = mp->key;
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struct mapping *mp = mappings + HASH_POSITION (ht, key);
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int (*equals) (const void *, const void *) = ht->test_function;
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if (EMPTY_ENTRY_P (mp_key))
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return -1;
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else if (DELETED_ENTRY_P (mp_key)
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|| !ht->test_function (key, mp_key))
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{
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if (++location == size)
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location = 0;
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}
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else
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return location;
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}
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LOOP_NON_EMPTY (mp, mappings, size)
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if (equals (key, mp->key))
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return mp;
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return NULL;
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}
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/* Get the value that corresponds to the key KEY in the hash table HT.
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@ -245,11 +237,11 @@ find_mapping (struct hash_table *ht, const void *key)
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void *
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hash_table_get (struct hash_table *ht, const void *key)
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{
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int location = find_mapping (ht, key);
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if (location < 0)
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return NULL;
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struct mapping *mp = find_mapping (ht, key);
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if (mp)
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return mp->value;
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else
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return ht->mappings[location].value;
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return NULL;
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}
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/* Like hash_table_get, but writes out the pointers to both key and
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@ -259,18 +251,18 @@ int
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hash_table_get_pair (struct hash_table *ht, const void *lookup_key,
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void *orig_key, void *value)
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{
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int location = find_mapping (ht, lookup_key);
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if (location < 0)
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return 0;
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else
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struct mapping *mp = find_mapping (ht, lookup_key);
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if (mp)
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{
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struct mapping *mp = ht->mappings + location;
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if (orig_key)
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*(void **)orig_key = mp->key;
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if (value)
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*(void **)value = mp->value;
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return 1;
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}
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else
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return 0;
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}
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/* Return 1 if KEY exists in HT, 0 otherwise. */
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@ -278,7 +270,7 @@ hash_table_get_pair (struct hash_table *ht, const void *lookup_key,
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int
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hash_table_exists (struct hash_table *ht, const void *key)
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{
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return find_mapping (ht, key) >= 0;
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return find_mapping (ht, key) != NULL;
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}
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#define MAX(i, j) (((i) >= (j)) ? (i) : (j))
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@ -289,46 +281,27 @@ hash_table_exists (struct hash_table *ht, const void *key)
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static void
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grow_hash_table (struct hash_table *ht)
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{
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int i;
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struct mapping *old_mappings = ht->mappings;
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struct mapping *old_end = ht->mappings + ht->size;
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struct mapping *mp;
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int old_count = ht->count; /* for assert() below */
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int old_size = ht->size;
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/* To minimize the number of regrowth, we'd like to resize the hash
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table exponentially. Normally, this would be done by doubling
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ht->size (and round it to next prime) on each regrow:
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ht->size = prime_size (ht->size * 2);
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But it is possible that the table has large fullness because of
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the many deleted entries. If that is the case, we don't want to
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blindly grow the table; we just want to rehash it. For that
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reason, we use ht->count as the relevant parameter. MAX is used
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only because we don't want to actually shrink the table. (But
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maybe that's wrong.) */
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int needed_size = prime_size (ht->count * 3);
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ht->size = MAX (old_size, needed_size);
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#if 0
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printf ("growing from %d to %d\n", old_size, ht->size);
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printf ("growing from %d to %d\n", ht->size, prime_size (ht->size * 2));
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#endif
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ht->size = prime_size (ht->size * 2);
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ht->mappings = xmalloc (ht->size * sizeof (struct mapping));
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memset (ht->mappings, '\0', ht->size * sizeof (struct mapping));
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/* Need to reset these two; hash_table_put will reinitialize them. */
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ht->fullness = 0;
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/* Need to reset this; hash_table_put will reinitialize it. */
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ht->count = 0;
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for (i = 0; i < old_size; i++)
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{
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struct mapping *mp = old_mappings + i;
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void *mp_key = mp->key;
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if (!EMPTY_ENTRY_P (mp_key)
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&& !DELETED_ENTRY_P (mp_key))
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hash_table_put (ht, mp_key, mp->value);
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}
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for (mp = old_mappings; mp < old_end; mp++)
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if (!EMPTY_MAPPING_P (mp))
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hash_table_put (ht, mp->key, mp->value);
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assert (ht->count == old_count);
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xfree (old_mappings);
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}
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@ -339,86 +312,71 @@ grow_hash_table (struct hash_table *ht)
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void
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hash_table_put (struct hash_table *ht, const void *key, void *value)
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{
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/* Cannot use find_mapping here because we're actually looking for
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an *empty* entry. */
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struct mapping *mappings = ht->mappings;
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int size = ht->size;
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int location = ht->hash_function (key) % size;
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while (1)
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{
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struct mapping *mp = mappings + location;
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void *mp_key = mp->key;
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int (*equals) (const void *, const void *) = ht->test_function;
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if (EMPTY_ENTRY_P (mp_key))
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{
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++ht->fullness;
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++ht->count;
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just_insert:
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mp->key = (void *)key; /* const? */
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mp->value = value;
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break;
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}
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else if (DELETED_ENTRY_P (mp_key)
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|| !ht->test_function (key, mp_key))
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{
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if (++location == size)
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location = 0;
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}
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else /* equal to key and not deleted */
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{
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/* We're replacing an existing entry, so ht->count and
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ht->fullness remain unchanged. */
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goto just_insert;
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}
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}
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if (ht->fullness * 4 > ht->size * 3)
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/* When fullness exceeds 75% of size, regrow the table. */
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struct mapping *mp = mappings + HASH_POSITION (ht, key);
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LOOP_NON_EMPTY (mp, mappings, size)
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if (equals (key, mp->key))
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{
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mp->key = (void *)key; /* const? */
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mp->value = value;
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return;
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}
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++ht->count;
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mp->key = (void *)key; /* const? */
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mp->value = value;
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if (ht->count > ht->size * 3 / 4)
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/* When table is 75% full, regrow it. */
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grow_hash_table (ht);
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}
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/* Remove KEY from HT. */
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/* Remove a mapping that matches KEY from HT. Return 0 if there was
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no such entry; return 1 if an entry was removed. */
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int
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hash_table_remove (struct hash_table *ht, const void *key)
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{
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int location = find_mapping (ht, key);
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if (location < 0)
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struct mapping *mp = find_mapping (ht, key);
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if (!mp)
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return 0;
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else
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{
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int size = ht->size;
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struct mapping *mappings = ht->mappings;
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struct mapping *mp = mappings + location;
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/* We don't really remove an entry from the hash table: we just
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mark it as deleted. This is because there may be other
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entries located after this entry whose hash points to a
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location before this entry. (Example: keys A, B and C have
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the same hash. If you were to really *delete* B from the
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table, C could no longer be found.) */
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/* Optimization addendum: if the mapping that follows LOCATION
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is already empty, that is a sure sign that nobody depends on
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LOCATION being non-empty. (This is because we're using
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linear probing. This would not be the case with double
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hashing.) In that case, we may safely delete the mapping. */
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/* This could be generalized so that the all the non-empty
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locations following LOCATION are simply shifted leftward. It
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would make deletion a bit slower, but it would remove the
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ugly DELETED_ENTRY_P checks from all the rest of the code,
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making the whole thing faster. */
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int location_after = (location + 1) == ht->size ? 0 : location + 1;
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struct mapping *mp_after = mappings + location_after;
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if (EMPTY_ENTRY_P (mp_after->key))
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{
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mp->key = ENTRY_EMPTY;
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--ht->fullness;
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}
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else
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mp->key = ENTRY_DELETED;
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mp->key = NULL;
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--ht->count;
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/* Rehash all the entries following MP. The alternative
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approach is to mark entry as deleted, but that leaves a lot
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of garbage. More importantly, this method makes
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hash_table_get and hash_table_put measurably faster. */
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mp = NEXT_MAPPING (mp, mappings, size);
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LOOP_NON_EMPTY (mp, mappings, size)
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{
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const void *key2 = mp->key;
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struct mapping *mp_new = mappings + HASH_POSITION (ht, key2);
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/* Find the new location for the key. */
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LOOP_NON_EMPTY (mp_new, mappings, size)
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if (key2 == mp_new->key)
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/* The mapping MP (key2) is already where we want it (in
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MP_NEW's "chain" of keys.) */
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goto next_rehash;
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*mp_new = *mp;
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mp->key = NULL;
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next_rehash:
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;
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}
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return 1;
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}
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}
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@ -431,32 +389,36 @@ void
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hash_table_clear (struct hash_table *ht)
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{
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memset (ht->mappings, '\0', ht->size * sizeof (struct mapping));
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ht->fullness = 0;
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ht->count = 0;
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}
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/* Map MAPFUN over all the mappings in hash table HT. MAPFUN is
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called with three arguments: the key, the value, and the CLOSURE.
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Don't add or remove entries from HT while hash_table_map is being
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called, or strange things may happen. */
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|
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It is undefined what happens if you add or remove entries in the
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hash table while hash_table_map is running. The exception is the
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entry you're currently mapping over; you may remove or change that
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entry. */
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void
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hash_table_map (struct hash_table *ht,
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int (*mapfun) (void *, void *, void *),
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void *closure)
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{
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struct mapping *mappings = ht->mappings;
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int i;
|
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for (i = 0; i < ht->size; i++)
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{
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struct mapping *mp = mappings + i;
|
||||
void *mp_key = mp->key;
|
||||
struct mapping *mp = ht->mappings;
|
||||
struct mapping *end = ht->mappings + ht->size;
|
||||
|
||||
if (!EMPTY_ENTRY_P (mp_key)
|
||||
&& !DELETED_ENTRY_P (mp_key))
|
||||
if (mapfun (mp_key, mp->value, closure))
|
||||
for (; mp < end; mp++)
|
||||
if (!EMPTY_MAPPING_P (mp))
|
||||
{
|
||||
void *key;
|
||||
repeat:
|
||||
key = mp->key;
|
||||
if (mapfun (key, mp->value, closure))
|
||||
return;
|
||||
}
|
||||
if (mp->key != key && !EMPTY_MAPPING_P (mp))
|
||||
goto repeat;
|
||||
}
|
||||
}
|
||||
|
||||
/* Return the number of elements in the hash table. This is not the
|
||||
|
|
@ -470,21 +432,18 @@ hash_table_count (struct hash_table *ht)
|
|||
|
||||
/* Support for hash tables whose keys are strings. */
|
||||
|
||||
/* supposedly from the Dragon Book P436. */
|
||||
/* 31 bit hash function. Taken from Gnome's glib. This seems to
|
||||
perform much better than the above. */
|
||||
unsigned long
|
||||
string_hash (const void *sv)
|
||||
string_hash (const void *key)
|
||||
{
|
||||
unsigned int h = 0;
|
||||
unsigned const char *x = (unsigned const char *) sv;
|
||||
|
||||
while (*x)
|
||||
{
|
||||
unsigned int g;
|
||||
h = (h << 4) + *x++;
|
||||
if ((g = h & 0xf0000000) != 0)
|
||||
h = (h ^ (g >> 24)) ^ g;
|
||||
}
|
||||
|
||||
const char *p = key;
|
||||
unsigned int h = *p;
|
||||
|
||||
if (h)
|
||||
for (p += 1; *p != '\0'; p++)
|
||||
h = (h << 5) - h + *p;
|
||||
|
||||
return h;
|
||||
}
|
||||
|
||||
|
|
@ -557,7 +516,7 @@ main (void)
|
|||
if (!hash_table_exists (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))
|
||||
|
|
@ -572,7 +531,7 @@ main (void)
|
|||
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;
|
||||
}
|
||||
|
|
|
|||
Loading…
Reference in New Issue