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 uint32_t *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     free (htab->entries[i]);
 146
 147   if (htab->free)
 148     htab->free (htab->entries);
 149   free (htab);
 150 }
 151
 152 /* Similar to htab_find_slot, but without several unwanted side effects:
 153     - Does not call htab->eq_f when it finds an existing entry.
 154     - Does not change the count of elements/searches/collisions in the
 155       hash table.
 156    This function also assumes there are no deleted entries in the table.
 157    HASH is the hash value for the element to be inserted.  */
 158
 159 inline static void **
 160 find_empty_slot_for_expand (struct hashtab *htab, int hash)
 161 {
 162   size_t size = htab->size;
 163   unsigned int index = hash % size;
 164   void **slot = htab->entries + index;
 165   int hash2;
 166
 167   if (! *slot)
 168     return slot;
 169
 170   hash2 = 1 + hash % (size - 2);
 171   for (;;)
 172     {
 173       index += hash2;
 174       if (index >= size)
 175         index -= size;
 176
 177       slot = htab->entries + index;
 178       if (! *slot)
 179         return slot;
 180     }
 181 }
 182
 183 /* The following function changes size of memory allocated for the
 184    entries and repeatedly inserts the table elements.  The occupancy
 185    of the table after the call will be about 50%.  Naturally the hash
 186    table must already exist.  Remember also that the place of the
 187    table entries is changed.  If memory allocation failures are allowed,
 188    this function will return zero, indicating that the table could not be
 189    expanded.  If all goes well, it will return a non-zero value.  */
 190
 191 inline static int
 192 htab_expand (struct hashtab *htab, int (*hash_fn) (void *))
 193 {
 194   void **oentries;
 195   void **olimit;
 196   void **p;
 197   void **nentries;
 198   size_t nsize;
 199
 200   oentries = htab->entries;
 201   olimit = oentries + htab->size;
 202
 203   /* Resize only when table after removal of unused elements is either
 204      too full or too empty.  */
 205   if (htab->n_elements * 2 > htab->size)
 206     nsize = higher_prime_number (htab->n_elements * 2);
 207   else
 208     nsize = htab->size;
 209
 210   nentries = malloc (sizeof (void *) * nsize);
 211   memset (nentries, 0, sizeof (void *) * nsize);
 212   if (nentries == NULL)
 213     return 0;
 214   htab->entries = nentries;
 215   htab->size = nsize;
 216
 217   p = oentries;
 218   do
 219     {
 220       if (*p)
 221         *find_empty_slot_for_expand (htab, hash_fn (*p))
 222           = *p;
 223
 224       p++;
 225     }
 226   while (p < olimit);
 227
 228   /* Without recording the free corresponding to the malloc used to
 229      allocate the table, we couldn't tell whether this was allocated
 230      by the malloc() built into ld.so or the one in the main
 231      executable or libc.  Calling free() for something that was
 232      allocated by the early malloc(), rather than the final run-time
 233      malloc() could do Very Bad Things (TM).  We will waste memory
 234      allocated early as long as there's no corresponding free(), but
 235      this isn't so much memory as to be significant.  */
 236
 237   if (htab->free)
 238     htab->free (oentries);
 239
 240   /* Use the free() corresponding to the malloc() above to free this
 241      up.  */
 242   htab->free = free;
 243
 244   return 1;
 245 }
 246
 247 /* This function searches for a hash table slot containing an entry
 248    equal to the given element.  To delete an entry, call this with
 249    INSERT = 0, then call htab_clear_slot on the slot returned (possibly
 250    after doing some checks).  To insert an entry, call this with
 251    INSERT = 1, then write the value you want into the returned slot.
 252    When inserting an entry, NULL may be returned if memory allocation
 253    fails.  */
 254
 255 inline static void **
 256 htab_find_slot (struct hashtab *htab, void *ptr, int insert,
 257                 int (*hash_fn)(void *), int (*eq_fn)(void *, void *))
 258 {
 259   unsigned int index;
 260   int hash, hash2;
 261   size_t size;
 262   void **entry;
 263
 264   if (htab->size * 3 <= htab->n_elements * 4
 265       && htab_expand (htab, hash_fn) == 0)
 266     return NULL;
 267
 268   hash = hash_fn (ptr);
 269
 270   size = htab->size;
 271   index = hash % size;
 272
 273   entry = &htab->entries[index];
 274   if (!*entry)
 275     goto empty_entry;
 276   else if (eq_fn (*entry, ptr))
 277     return entry;
 278
 279   hash2 = 1 + hash % (size - 2);
 280   for (;;)
 281     {
 282       index += hash2;
 283       if (index >= size)
 284         index -= size;
 285
 286       entry = &htab->entries[index];
 287       if (!*entry)
 288         goto empty_entry;
 289       else if (eq_fn (*entry, ptr))
 290         return entry;
 291     }
 292
 293  empty_entry:
 294   if (!insert)
 295     return NULL;
 296
 297   htab->n_elements++;
 298   return entry;
 299 }
 300
 301 #endif /* INLINE_HASHTAB_H */