include/inline-hashtab.h

   1 /* Fully-inline hash table, used mainly for managing TLS descriptors.
   2
   3    Copyright (C) 1999, 2000, 2001, 2002, 2003, 2005, 2008
   4      Free Software Foundation, Inc.
   5    This file is part of the GNU C Library.
   6    Contributed by Alexandre Oliva  <aoliva@redhat.com>
   7
   8    This file is derived from a 2003's version of libiberty's
   9    hashtab.c, contributed by Vladimir Makarov (vmakarov@cygnus.com),
  10    but with most adaptation points and support for deleting elements
  11    removed.
  12
  13    The GNU C Library is free software; you can redistribute it and/or
  14    modify it under the terms of the GNU Lesser General Public
  15    License as published by the Free Software Foundation; either
  16    version 2.1 of the License, or (at your option) any later version.
  17
  18    The GNU C Library is distributed in the hope that it will be useful,
  19    but WITHOUT ANY WARRANTY; without even the implied warranty of
  20    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  21    Lesser General Public License for more details.
  22
  23    You should have received a copy of the GNU Lesser General Public
  24    License along with the GNU C Library; if not, write to the Free
  25    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  26    02111-1307 USA.  */
  27
  28 #ifndef INLINE_HASHTAB_H
  29 # define INLINE_HASHTAB_H 1
  30
  31 extern void weak_function free (void *ptr);
  32
  33 inline static unsigned long
  34 higher_prime_number (unsigned long n)
  35 {
  36   /* These are primes that are near, but slightly smaller than, a
  37      power of two.  */
  38   static const uint32_t primes[] = {
  39     UINT32_C (7),
  40     UINT32_C (13),
  41     UINT32_C (31),
  42     UINT32_C (61),
  43     UINT32_C (127),
  44     UINT32_C (251),
  45     UINT32_C (509),
  46     UINT32_C (1021),
  47     UINT32_C (2039),
  48     UINT32_C (4093),
  49     UINT32_C (8191),
  50     UINT32_C (16381),
  51     UINT32_C (32749),
  52     UINT32_C (65521),
  53     UINT32_C (131071),
  54     UINT32_C (262139),
  55     UINT32_C (524287),
  56     UINT32_C (1048573),
  57     UINT32_C (2097143),
  58     UINT32_C (4194301),
  59     UINT32_C (8388593),
  60     UINT32_C (16777213),
  61     UINT32_C (33554393),
  62     UINT32_C (67108859),
  63     UINT32_C (134217689),
  64     UINT32_C (268435399),
  65     UINT32_C (536870909),
  66     UINT32_C (1073741789),
  67     UINT32_C (2147483647),
  68                                         /* 4294967291L */
  69     UINT32_C (2147483647) + UINT32_C (2147483644)
  70   };
  71
  72   const uint32_t *low = &primes[0];
  73   const uint32_t *high = &primes[sizeof (primes) / sizeof (primes[0])];
  74
  75   while (low != high)
  76     {
  77       const unsigned long *mid = low + (high - low) / 2;
  78       if (n > *mid)
  79         low = mid + 1;
  80       else
  81         high = mid;
  82     }
  83
  84 #if 0
  85   /* If we've run out of primes, abort.  */
  86   if (n > *low)
  87     {
  88       fprintf (stderr, "Cannot find prime bigger than %lu\n", n);
  89       abort ();
  90     }
  91 #endif
  92
  93   return *low;
  94 }
  95
  96 struct hashtab
  97 {
  98   /* Table itself.  */
  99   void **entries;
 100
 101   /* Current size (in entries) of the hash table */
 102   size_t size;
 103
 104   /* Current number of elements.  */
 105   size_t n_elements;
 106
 107   /* Free function for the entries array.  This may vary depending on
 108      how early the array was allocated.  If it is NULL, then the array
 109      can't be freed.  */
 110   void (*free) (void *ptr);
 111 };
 112
 113 inline static struct hashtab *
 114 htab_create (void)
 115 {
 116   struct hashtab *ht = malloc (sizeof (struct hashtab));
 117
 118   if (! ht)
 119     return NULL;
 120   ht->size = 3;
 121   ht->entries = malloc (sizeof (void *) * ht->size);
 122   ht->free = free;
 123   if (! ht->entries)
 124     {
 125       if (ht->free)
 126         ht->free (ht);
 127       return NULL;
 128     }
 129
 130   ht->n_elements = 0;
 131
 132   memset (ht->entries, 0, sizeof (void *) * ht->size);
 133
 134   return ht;
 135 }
 136
 137 /* This is only called from _dl_unmap, so it's safe to call
 138    free().  */
 139 inline static void
 140 htab_delete (struct hashtab *htab)
 141 {
 142   int i;
 143
 144   for (i = htab->size - 1; i >= 0; i--)
 145     if (htab->entries[i])
 146       free (htab->entries[i]);
 147
 148   if (htab->free)
 149     htab->free (htab->entries);
 150   free (htab);
 151 }
 152
 153 /* Similar to htab_find_slot, but without several unwanted side effects:
 154     - Does not call htab->eq_f when it finds an existing entry.
 155     - Does not change the count of elements/searches/collisions in the
 156       hash table.
 157    This function also assumes there are no deleted entries in the table.
 158    HASH is the hash value for the element to be inserted.  */
 159
 160 inline static void **
 161 find_empty_slot_for_expand (struct hashtab *htab, int hash)
 162 {
 163   size_t size = htab->size;
 164   unsigned int index = hash % size;
 165   void **slot = htab->entries + index;
 166   int hash2;
 167
 168   if (! *slot)
 169     return slot;
 170
 171   hash2 = 1 + hash % (size - 2);
 172   for (;;)
 173     {
 174       index += hash2;
 175       if (index >= size)
 176         index -= size;
 177
 178       slot = htab->entries + index;
 179       if (! *slot)
 180         return slot;
 181     }
 182 }
 183
 184 /* The following function changes size of memory allocated for the
 185    entries and repeatedly inserts the table elements.  The occupancy
 186    of the table after the call will be about 50%.  Naturally the hash
 187    table must already exist.  Remember also that the place of the
 188    table entries is changed.  If memory allocation failures are allowed,
 189    this function will return zero, indicating that the table could not be
 190    expanded.  If all goes well, it will return a non-zero value.  */
 191
 192 inline static int
 193 htab_expand (struct hashtab *htab, int (*hash_fn) (void *))
 194 {
 195   void **oentries;
 196   void **olimit;
 197   void **p;
 198   void **nentries;
 199   size_t nsize;
 200
 201   oentries = htab->entries;
 202   olimit = oentries + htab->size;
 203
 204   /* Resize only when table after removal of unused elements is either
 205      too full or too empty.  */
 206   if (htab->n_elements * 2 > htab->size)
 207     nsize = higher_prime_number (htab->n_elements * 2);
 208   else
 209     nsize = htab->size;
 210
 211   nentries = malloc (sizeof (void *) * nsize);
 212   memset (nentries, 0, sizeof (void *) * nsize);
 213   if (nentries == NULL)
 214     return 0;
 215   htab->entries = nentries;
 216   htab->size = nsize;
 217
 218   p = oentries;
 219   do
 220     {
 221       if (*p)
 222         *find_empty_slot_for_expand (htab, hash_fn (*p))
 223           = *p;
 224
 225       p++;
 226     }
 227   while (p < olimit);
 228
 229   /* Without recording the free corresponding to the malloc used to
 230      allocate the table, we couldn't tell whether this was allocated
 231      by the malloc() built into ld.so or the one in the main
 232      executable or libc.  Calling free() for something that was
 233      allocated by the early malloc(), rather than the final run-time
 234      malloc() could do Very Bad Things (TM).  We will waste memory
 235      allocated early as long as there's no corresponding free(), but
 236      this isn't so much memory as to be significant.  */
 237
 238   if (htab->free)
 239     htab->free (oentries);
 240
 241   /* Use the free() corresponding to the malloc() above to free this
 242      up.  */
 243   htab->free = free;
 244
 245   return 1;
 246 }
 247
 248 /* This function searches for a hash table slot containing an entry
 249    equal to the given element.  To delete an entry, call this with
 250    INSERT = 0, then call htab_clear_slot on the slot returned (possibly
 251    after doing some checks).  To insert an entry, call this with
 252    INSERT = 1, then write the value you want into the returned slot.
 253    When inserting an entry, NULL may be returned if memory allocation
 254    fails.  */
 255
 256 inline static void **
 257 htab_find_slot (struct hashtab *htab, void *ptr, int insert,
 258                 int (*hash_fn)(void *), int (*eq_fn)(void *, void *))
 259 {
 260   unsigned int index;
 261   int hash, hash2;
 262   size_t size;
 263   void **entry;
 264
 265   if (htab->size * 3 <= htab->n_elements * 4
 266       && htab_expand (htab, hash_fn) == 0)
 267     return NULL;
 268
 269   hash = hash_fn (ptr);
 270
 271   size = htab->size;
 272   index = hash % size;
 273
 274   entry = &htab->entries[index];
 275   if (!*entry)
 276     goto empty_entry;
 277   else if (eq_fn (*entry, ptr))
 278     return entry;
 279
 280   hash2 = 1 + hash % (size - 2);
 281   for (;;)
 282     {
 283       index += hash2;
 284       if (index >= size)
 285         index -= size;
 286
 287       entry = &htab->entries[index];
 288       if (!*entry)
 289         goto empty_entry;
 290       else if (eq_fn (*entry, ptr))
 291         return entry;
 292     }
 293
 294  empty_entry:
 295   if (!insert)
 296     return NULL;
 297
 298   htab->n_elements++;
 299   return entry;
 300 }
 301
 302 #endif /* INLINE_HASHTAB_H */