file, but you are not obligated to do so. If you do not wish to do
so, delete this exception statement from your version. */
-#ifdef HAVE_CONFIG_H
+/* With -DSTANDALONE, this file can be compiled outside Wget source
+ tree. To test, also use -DTEST. */
+
+#ifndef STANDALONE
# include <config.h>
+# ifdef HAVE_STRING_H
+# include <string.h>
+# else
+# include <strings.h>
+# endif
+# ifdef HAVE_LIMITS_H
+# include <limits.h>
+# endif
+#else
+/* If running without Autoconf, go ahead and assume presence of
+ standard C89 headers. */
+# include <string.h>
+# include <limits.h>
#endif
-#ifdef HAVE_STRING_H
-# include <string.h>
-#else
-# include <strings.h>
-#endif /* HAVE_STRING_H */
+#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
-#include "wget.h"
-#include "utils.h"
-
-#include "hash.h"
-
-#ifdef STANDALONE
-# undef xmalloc
-# undef xrealloc
-# undef xfree
-
-# define xmalloc malloc
-# define xrealloc realloc
+#ifndef STANDALONE
+/* Get Wget's utility headers. */
+# include "wget.h"
+# include "utils.h"
+#else
+/* Make do without them. */
+# define xnew(x) xmalloc (sizeof (x))
+# define xnew_array(type, x) xmalloc (sizeof (type) * (x))
+# define xmalloc malloc /* or something that exits
+ if not enough memory */
# define xfree free
-
-# undef TOLOWER
+# define countof(x) (sizeof (x) / sizeof ((x)[0]))
# define TOLOWER(x) ('A' <= (x) && (x) <= 'Z' ? (x) - 32 : (x))
+# define PARAMS(x) x
#endif
+#include "hash.h"
+
/* INTERFACE:
Hash tables are a technique used to implement mapping between
The hash table is implemented as an open-addressed table with
linear probing collision resolution.
- For those not up to CS parlance, it means that all the hash entries
- (pairs of pointers key and value) are stored in a contiguous array.
- The position of each mapping 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 placed at the next empty position following the
- occupied place. This collision resolution technique is called
- "linear probing".
+ The above means that all the hash entries (pairs of pointers, key
+ and value) are stored in a contiguous array. The position of each
+ mapping 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
+ placed at the next empty position following the occupied place.
+ 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
the prime table. */
};
-/* We use all-bit-set marker to mean that a mapping is empty. It is
- (hopefully) illegal as a pointer, and it allows the users to use
- NULL (as well as any non-negative integer) as key. */
-#define NON_EMPTY(mp) (mp->key != (void *)~(unsigned long)0)
+/* We use the all-bits-set constant (INVALID_PTR) marker to mean that
+ a mapping is empty. It is unaligned and therefore illegal as a
+ pointer. INVALID_PTR_BYTE (0xff) is the one-byte value used to
+ initialize the mappings 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 *) ~(unsigned long)0)
+#ifndef UCHAR_MAX
+# define UCHAR_MAX 0xff
+#endif
+#define INVALID_PTR_BYTE UCHAR_MAX
+
+#define NON_EMPTY(mp) ((mp)->key != INVALID_PTR)
+#define MARK_AS_EMPTY(mp) ((mp)->key = INVALID_PTR)
/* "Next" mapping is the mapping after MP, but wrapping back to
MAPPINGS when MP would reach MAPPINGS+SIZE. */
for (; NON_EMPTY (mp); mp = NEXT_MAPPING (mp, mappings, size))
/* Return the position of KEY in hash table SIZE large, hash function
- being HASHFUN. #### Some implementations multiply HASHFUN's output
- with the table's "golden ratio" to get better spreading of keys.
- I'm not sure if that is necessary with our hash functions. */
+ being HASHFUN. */
#define HASH_POSITION(key, hashfun, size) ((hashfun) (key) % size)
-/* Find a prime near, but greather than or equal to SIZE. Of course,
- the primes are not calculated, but looked up from a table. The
- table does not contain all primes in range, just a selection useful
+/* Find a prime near, but greather 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
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. If,
- instead of that, you want strings with equal contents to hash the
- same, use make_string_hash_table. */
+ 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,
/*assert (ht->resize_threshold >= items);*/
ht->mappings = xnew_array (struct mapping, ht->size);
+
/* Mark mappings as empty. We use 0xff rather than 0 to mark empty
- keys because it allows us to store NULL keys to the table. */
- memset (ht->mappings, 0xff, size * sizeof (struct mapping));
+ keys because it allows us to use NULL/0 as keys. */
+ memset (ht->mappings, INVALID_PTR_BYTE, size * sizeof (struct mapping));
ht->count = 0;
ht->resize_threshold = newsize * HASH_MAX_FULLNESS;
mappings = xnew_array (struct mapping, newsize);
- memset (mappings, 0xff, newsize * sizeof (struct mapping));
+ memset (mappings, INVALID_PTR_BYTE, newsize * sizeof (struct mapping));
ht->mappings = mappings;
for (mp = old_mappings; mp < old_end; mp++)
struct mapping *mappings = ht->mappings;
hashfun_t hasher = ht->hash_function;
- mp->key = NULL;
+ MARK_AS_EMPTY (mp);
--ht->count;
/* Rehash all the entries following MP. The alternative
goto next_rehash;
*mp_new = *mp;
- mp->key = NULL;
+ MARK_AS_EMPTY (mp);
next_rehash:
;
void
hash_table_clear (struct hash_table *ht)
{
- memset (ht->mappings, 0xff, ht->size * sizeof (struct mapping));
+ memset (ht->mappings, INVALID_PTR_BYTE, ht->size * sizeof (struct mapping));
ht->count = 0;
}
return hash_table_new (items, string_hash_nocase, string_cmp_nocase);
}
-/* Hashing of pointers. Used for hash tables that are keyed by
- pointer identity. (Common Lisp calls them EQ hash tables, and Java
- calls them IdentityHashMaps.) */
+/* 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. It offers excellent
+ spreading of values and doesn't need to know the hash table size to
+ work (unlike the very popular Knuth's multiplication hash). */
static unsigned long
ptrhash (const void *ptr)
return ptr1 == ptr2;
}
\f
-#ifdef STANDALONE
+#ifdef TEST
#include <stdio.h>
#include <string.h>
#endif
return 0;
}
-#endif
+#endif /* TEST */
projects / wget / blobdiff