include/inline-hashtab.h

   1 /* Fully-inline hash table, used mainly for managing TLS descriptors.
   2    Copyright (C) 1999-2018 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Alexandre Oliva  <aoliva@redhat.com>
   5
   6    This file is derived from a 2003's version of libiberty's
   7    hashtab.c, contributed by Vladimir Makarov (vmakarov@cygnus.com),
   8    but with most adaptation points and support for deleting elements
   9    removed.
  10
  11    The GNU C Library is free software; you can redistribute it and/or
  12    modify it under the terms of the GNU Lesser General Public
  13    License as published by the Free Software Foundation; either
  14    version 2.1 of the License, or (at your option) any later version.
  15
  16    The GNU C Library is distributed in the hope that it will be useful,
  17    but WITHOUT ANY WARRANTY; without even the implied warranty of
  18    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19    Lesser General Public License for more details.
  20
  21    You should have received a copy of the GNU Lesser General Public
  22    License along with the GNU C Library; if not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 #ifndef INLINE_HASHTAB_H
  26 # define INLINE_HASHTAB_H 1
  27
  28 extern void weak_function free (void *ptr);
  29
  30 struct hashtab
  31 {
  32   /* Table itself.  */
  33   void **entries;
  34
  35   /* Current size (in entries) of the hash table */
  36   size_t size;
  37
  38   /* Current number of elements.  */
  39   size_t n_elements;
  40
  41   /* Free function for the entries array.  This may vary depending on
  42      how early the array was allocated.  If it is NULL, then the array
  43      can't be freed.  */
  44   void (*free) (void *ptr);
  45 };
  46
  47 inline static struct hashtab *
  48 htab_create (void)
  49 {
  50   struct hashtab *ht = malloc (sizeof (struct hashtab));
  51
  52   if (! ht)
  53     return NULL;
  54   ht->size = 3;
  55   ht->entries = malloc (sizeof (void *) * ht->size);
  56   ht->free = free;
  57   if (! ht->entries)
  58     {
  59       if (ht->free)
  60         ht->free (ht);
  61       return NULL;
  62     }
  63
  64   ht->n_elements = 0;
  65
  66   memset (ht->entries, 0, sizeof (void *) * ht->size);
  67
  68   return ht;
  69 }
  70
  71 /* This is only called from _dl_unmap, so it's safe to call
  72    free().  */
  73 inline static void
  74 htab_delete (struct hashtab *htab)
  75 {
  76   int i;
  77
  78   for (i = htab->size - 1; i >= 0; i--)
  79     free (htab->entries[i]);
  80
  81   if (htab->free)
  82     htab->free (htab->entries);
  83   free (htab);
  84 }
  85
  86 /* Similar to htab_find_slot, but without several unwanted side effects:
  87     - Does not call htab->eq_f when it finds an existing entry.
  88     - Does not change the count of elements/searches/collisions in the
  89       hash table.
  90    This function also assumes there are no deleted entries in the table.
  91    HASH is the hash value for the element to be inserted.  */
  92
  93 inline static void **
  94 find_empty_slot_for_expand (struct hashtab *htab, int hash)
  95 {
  96   size_t size = htab->size;
  97   unsigned int index = hash % size;
  98   void **slot = htab->entries + index;
  99   int hash2;
 100
 101   if (! *slot)
 102     return slot;
 103
 104   hash2 = 1 + hash % (size - 2);
 105   for (;;)
 106     {
 107       index += hash2;
 108       if (index >= size)
 109         index -= size;
 110
 111       slot = htab->entries + index;
 112       if (! *slot)
 113         return slot;
 114     }
 115 }
 116
 117 /* The following function changes size of memory allocated for the
 118    entries and repeatedly inserts the table elements.  The occupancy
 119    of the table after the call will be about 50%.  Naturally the hash
 120    table must already exist.  Remember also that the place of the
 121    table entries is changed.  If memory allocation failures are allowed,
 122    this function will return zero, indicating that the table could not be
 123    expanded.  If all goes well, it will return a non-zero value.  */
 124
 125 inline static int
 126 htab_expand (struct hashtab *htab, int (*hash_fn) (void *))
 127 {
 128   void **oentries;
 129   void **olimit;
 130   void **p;
 131   void **nentries;
 132   size_t nsize;
 133
 134   oentries = htab->entries;
 135   olimit = oentries + htab->size;
 136
 137   /* Resize only when table after removal of unused elements is either
 138      too full or too empty.  */
 139   if (htab->n_elements * 2 > htab->size)
 140     nsize = _dl_higher_prime_number (htab->n_elements * 2);
 141   else
 142     nsize = htab->size;
 143
 144   nentries = calloc (sizeof (void *), nsize);
 145   if (nentries == NULL)
 146     return 0;
 147   htab->entries = nentries;
 148   htab->size = nsize;
 149
 150   p = oentries;
 151   do
 152     {
 153       if (*p)
 154         *find_empty_slot_for_expand (htab, hash_fn (*p))
 155           = *p;
 156
 157       p++;
 158     }
 159   while (p < olimit);
 160
 161   /* Without recording the free corresponding to the malloc used to
 162      allocate the table, we couldn't tell whether this was allocated
 163      by the malloc() built into ld.so or the one in the main
 164      executable or libc.  Calling free() for something that was
 165      allocated by the early malloc(), rather than the final run-time
 166      malloc() could do Very Bad Things (TM).  We will waste memory
 167      allocated early as long as there's no corresponding free(), but
 168      this isn't so much memory as to be significant.  */
 169
 170   if (htab->free)
 171     htab->free (oentries);
 172
 173   /* Use the free() corresponding to the malloc() above to free this
 174      up.  */
 175   htab->free = free;
 176
 177   return 1;
 178 }
 179
 180 /* This function searches for a hash table slot containing an entry
 181    equal to the given element.  To delete an entry, call this with
 182    INSERT = 0, then call htab_clear_slot on the slot returned (possibly
 183    after doing some checks).  To insert an entry, call this with
 184    INSERT = 1, then write the value you want into the returned slot.
 185    When inserting an entry, NULL may be returned if memory allocation
 186    fails.  */
 187
 188 inline static void **
 189 htab_find_slot (struct hashtab *htab, void *ptr, int insert,
 190                 int (*hash_fn)(void *), int (*eq_fn)(void *, void *))
 191 {
 192   unsigned int index;
 193   int hash, hash2;
 194   size_t size;
 195   void **entry;
 196
 197   if (htab->size * 3 <= htab->n_elements * 4
 198       && htab_expand (htab, hash_fn) == 0)
 199     return NULL;
 200
 201   hash = hash_fn (ptr);
 202
 203   size = htab->size;
 204   index = hash % size;
 205
 206   entry = &htab->entries[index];
 207   if (!*entry)
 208     goto empty_entry;
 209   else if (eq_fn (*entry, ptr))
 210     return entry;
 211
 212   hash2 = 1 + hash % (size - 2);
 213   for (;;)
 214     {
 215       index += hash2;
 216       if (index >= size)
 217         index -= size;
 218
 219       entry = &htab->entries[index];
 220       if (!*entry)
 221         goto empty_entry;
 222       else if (eq_fn (*entry, ptr))
 223         return entry;
 224     }
 225
 226  empty_entry:
 227   if (!insert)
 228     return NULL;
 229
 230   htab->n_elements++;
 231   return entry;
 232 }
 233
 234 #endif /* INLINE_HASHTAB_H */