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/* Fully-inline hash table, used mainly for managing TLS descriptors.
Copyright (C) 1999-2014 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Alexandre Oliva <>
This file is derived from a 2003's version of libiberty's
hashtab.c, contributed by Vladimir Makarov (,
but with most adaptation points and support for deleting elements
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<>. */
extern void weak_function free (void *ptr);
struct hashtab
/* Table itself. */
void **entries;
/* Current size (in entries) of the hash table */
size_t size;
/* Current number of elements. */
size_t n_elements;
/* Free function for the entries array. This may vary depending on
how early the array was allocated. If it is NULL, then the array
can't be freed. */
void (*free) (void *ptr);
inline static struct hashtab *
htab_create (void)
struct hashtab *ht = malloc (sizeof (struct hashtab));
if (! ht)
return NULL;
ht->size = 3;
ht->entries = malloc (sizeof (void *) * ht->size);
ht->free = free;
if (! ht->entries)
if (ht->free)
ht->free (ht);
return NULL;
ht->n_elements = 0;
memset (ht->entries, 0, sizeof (void *) * ht->size);
return ht;
/* This is only called from _dl_unmap, so it's safe to call
free(). */
inline static void
htab_delete (struct hashtab *htab)
int i;
for (i = htab->size - 1; i >= 0; i--)
free (htab->entries[i]);
if (htab->free)
htab->free (htab->entries);
free (htab);
/* Similar to htab_find_slot, but without several unwanted side effects:
- Does not call htab->eq_f when it finds an existing entry.
- Does not change the count of elements/searches/collisions in the
hash table.
This function also assumes there are no deleted entries in the table.
HASH is the hash value for the element to be inserted. */
inline static void **
find_empty_slot_for_expand (struct hashtab *htab, int hash)
size_t size = htab->size;
unsigned int index = hash % size;
void **slot = htab->entries + index;
int hash2;
if (! *slot)
return slot;
hash2 = 1 + hash % (size - 2);
for (;;)
index += hash2;
if (index >= size)
index -= size;
slot = htab->entries + index;
if (! *slot)
return slot;
/* The following function changes size of memory allocated for the
entries and repeatedly inserts the table elements. The occupancy
of the table after the call will be about 50%. Naturally the hash
table must already exist. Remember also that the place of the
table entries is changed. If memory allocation failures are allowed,
this function will return zero, indicating that the table could not be
expanded. If all goes well, it will return a non-zero value. */
inline static int
htab_expand (struct hashtab *htab, int (*hash_fn) (void *))
void **oentries;
void **olimit;
void **p;
void **nentries;
size_t nsize;
oentries = htab->entries;
olimit = oentries + htab->size;
/* Resize only when table after removal of unused elements is either
too full or too empty. */
if (htab->n_elements * 2 > htab->size)
nsize = _dl_higher_prime_number (htab->n_elements * 2);
nsize = htab->size;
nentries = calloc (sizeof (void *), nsize);
if (nentries == NULL)
return 0;
htab->entries = nentries;
htab->size = nsize;
p = oentries;
if (*p)
*find_empty_slot_for_expand (htab, hash_fn (*p))
= *p;
while (p < olimit);
/* Without recording the free corresponding to the malloc used to
allocate the table, we couldn't tell whether this was allocated
by the malloc() built into or the one in the main
executable or libc. Calling free() for something that was
allocated by the early malloc(), rather than the final run-time
malloc() could do Very Bad Things (TM). We will waste memory
allocated early as long as there's no corresponding free(), but
this isn't so much memory as to be significant. */
if (htab->free)
htab->free (oentries);
/* Use the free() corresponding to the malloc() above to free this
up. */
htab->free = free;
return 1;
/* This function searches for a hash table slot containing an entry
equal to the given element. To delete an entry, call this with
INSERT = 0, then call htab_clear_slot on the slot returned (possibly
after doing some checks). To insert an entry, call this with
INSERT = 1, then write the value you want into the returned slot.
When inserting an entry, NULL may be returned if memory allocation
fails. */
inline static void **
htab_find_slot (struct hashtab *htab, void *ptr, int insert,
int (*hash_fn)(void *), int (*eq_fn)(void *, void *))
unsigned int index;
int hash, hash2;
size_t size;
void **entry;
if (htab->size * 3 <= htab->n_elements * 4
&& htab_expand (htab, hash_fn) == 0)
return NULL;
hash = hash_fn (ptr);
size = htab->size;
index = hash % size;
entry = &htab->entries[index];
if (!*entry)
goto empty_entry;
else if (eq_fn (*entry, ptr))
return entry;
hash2 = 1 + hash % (size - 2);
for (;;)
index += hash2;
if (index >= size)
index -= size;
entry = &htab->entries[index];
if (!*entry)
goto empty_entry;
else if (eq_fn (*entry, ptr))
return entry;
if (!insert)
return NULL;
return entry;
#endif /* INLINE_HASHTAB_H */