locale/programs/simple-hash.c

   1 /* Implement simple hashing table with string based keys.
   2    Copyright (C) 1994-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published
   7    by the Free Software Foundation; version 2 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #ifdef HAVE_CONFIG_H
  19 # include <config.h>
  20 #endif
  21
  22 #include <inttypes.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <stdint.h>
  27 #include <sys/types.h>
  28
  29 #include <obstack.h>
  30
  31 #ifdef HAVE_VALUES_H
  32 # include <values.h>
  33 #endif
  34
  35 #include "simple-hash.h"
  36
  37 #define obstack_chunk_alloc malloc
  38 #define obstack_chunk_free free
  39
  40 #ifndef BITSPERBYTE
  41 # define BITSPERBYTE 8
  42 #endif
  43
  44 #define hashval_t uint32_t
  45 #include "hashval.h"
  46
  47 #include <programs/xmalloc.h>
  48
  49 typedef struct hash_entry
  50 {
  51   unsigned long used;
  52   const void *key;
  53   size_t keylen;
  54   void *data;
  55   struct hash_entry *next;
  56 }
  57 hash_entry;
  58
  59 /* Prototypes for local functions.  */
  60 static void insert_entry_2 (hash_table *htab, const void *key, size_t keylen,
  61                             unsigned long hval, size_t idx, void *data);
  62 static size_t lookup (const hash_table *htab, const void *key, size_t keylen,
  63                       unsigned long int hval);
  64 static int is_prime (unsigned long int candidate);
  65
  66
  67 int
  68 init_hash (hash_table *htab, unsigned long int init_size)
  69 {
  70   /* We need the size to be a prime.  */
  71   init_size = next_prime (init_size);
  72
  73   /* Initialize the data structure.  */
  74   htab->size = init_size;
  75   htab->filled = 0;
  76   htab->first = NULL;
  77   htab->table = (void *) xcalloc (init_size + 1, sizeof (hash_entry));
  78   if (htab->table == NULL)
  79     return -1;
  80
  81   obstack_init (&htab->mem_pool);
  82
  83   return 0;
  84 }
  85
  86
  87 int
  88 delete_hash (hash_table *htab)
  89 {
  90   free (htab->table);
  91   obstack_free (&htab->mem_pool, NULL);
  92   return 0;
  93 }
  94
  95
  96 int
  97 insert_entry (hash_table *htab, const void *key, size_t keylen, void *data)
  98 {
  99   unsigned long int hval = compute_hashval (key, keylen);
 100   hash_entry *table = (hash_entry *) htab->table;
 101   size_t idx = lookup (htab, key, keylen, hval);
 102
 103   if (table[idx].used)
 104     /* We don't want to overwrite the old value.  */
 105     return -1;
 106   else
 107     {
 108       /* An empty bucket has been found.  */
 109       insert_entry_2 (htab, obstack_copy (&htab->mem_pool, key, keylen),
 110                       keylen, hval, idx, data);
 111       return 0;
 112     }
 113 }
 114
 115 static void
 116 insert_entry_2 (hash_table *htab, const void *key, size_t keylen,
 117                 unsigned long int hval, size_t idx, void *data)
 118 {
 119   hash_entry *table = (hash_entry *) htab->table;
 120
 121   table[idx].used = hval;
 122   table[idx].key = key;
 123   table[idx].keylen = keylen;
 124   table[idx].data = data;
 125
 126       /* List the new value in the list.  */
 127   if ((hash_entry *) htab->first == NULL)
 128     {
 129       table[idx].next = &table[idx];
 130       htab->first = &table[idx];
 131     }
 132   else
 133     {
 134       table[idx].next = ((hash_entry *) htab->first)->next;
 135       ((hash_entry *) htab->first)->next = &table[idx];
 136       htab->first = &table[idx];
 137     }
 138
 139   ++htab->filled;
 140   if (100 * htab->filled > 75 * htab->size)
 141     {
 142       /* Table is filled more than 75%.  Resize the table.
 143          Experiments have shown that for best performance, this threshold
 144          must lie between 40% and 85%.  */
 145       unsigned long int old_size = htab->size;
 146
 147       htab->size = next_prime (htab->size * 2);
 148       htab->filled = 0;
 149       htab->first = NULL;
 150       htab->table = (void *) xcalloc (1 + htab->size, sizeof (hash_entry));
 151
 152       for (idx = 1; idx <= old_size; ++idx)
 153         if (table[idx].used)
 154           insert_entry_2 (htab, table[idx].key, table[idx].keylen,
 155                           table[idx].used,
 156                           lookup (htab, table[idx].key, table[idx].keylen,
 157                                   table[idx].used),
 158                           table[idx].data);
 159
 160       free (table);
 161     }
 162 }
 163
 164
 165 int
 166 find_entry (const hash_table *htab, const void *key, size_t keylen,
 167             void **result)
 168 {
 169   hash_entry *table = (hash_entry *) htab->table;
 170   size_t idx = lookup (htab, key, keylen, compute_hashval (key, keylen));
 171
 172   if (table[idx].used == 0)
 173     return -1;
 174
 175   *result = table[idx].data;
 176   return 0;
 177 }
 178
 179
 180 int
 181 set_entry (hash_table *htab, const void *key, size_t keylen, void *newval)
 182 {
 183   hash_entry *table = (hash_entry *) htab->table;
 184   size_t idx = lookup (htab, key, keylen, compute_hashval (key, keylen));
 185
 186   if (table[idx].used == 0)
 187     return -1;
 188
 189   table[idx].data = newval;
 190   return 0;
 191 }
 192
 193
 194 int
 195 iterate_table (const hash_table *htab, void **ptr, const void **key,
 196                size_t *keylen, void **data)
 197 {
 198   if (*ptr == NULL)
 199     {
 200       if (htab->first == NULL)
 201         return -1;
 202       *ptr = (void *) ((hash_entry *) htab->first)->next;
 203     }
 204   else
 205     {
 206       if (*ptr == htab->first)
 207         return -1;
 208       *ptr = (void *) (((hash_entry *) *ptr)->next);
 209     }
 210
 211   *key = ((hash_entry *) *ptr)->key;
 212   *keylen = ((hash_entry *) *ptr)->keylen;
 213   *data = ((hash_entry *) *ptr)->data;
 214   return 0;
 215 }
 216
 217
 218 /* References:
 219    [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
 220    [Knuth]            The Art of Computer Programming, part3 (6.4) */
 221
 222 static size_t
 223 lookup (const hash_table *htab, const void *key, size_t keylen,
 224         unsigned long int hval)
 225 {
 226   unsigned long int hash;
 227   size_t idx;
 228   hash_entry *table = (hash_entry *) htab->table;
 229
 230   /* First hash function: simply take the modul but prevent zero.  */
 231   hash = 1 + hval % htab->size;
 232
 233   idx = hash;
 234
 235   if (table[idx].used)
 236     {
 237       if (table[idx].used == hval && table[idx].keylen == keylen
 238           && memcmp (table[idx].key, key, keylen) == 0)
 239         return idx;
 240
 241       /* Second hash function as suggested in [Knuth].  */
 242       hash = 1 + hval % (htab->size - 2);
 243
 244       do
 245         {
 246           if (idx <= hash)
 247             idx = htab->size + idx - hash;
 248           else
 249             idx -= hash;
 250
 251           /* If entry is found use it.  */
 252           if (table[idx].used == hval && table[idx].keylen == keylen
 253               && memcmp (table[idx].key, key, keylen) == 0)
 254             return idx;
 255         }
 256       while (table[idx].used);
 257     }
 258   return idx;
 259 }
 260
 261
 262 unsigned long int
 263 next_prime (unsigned long int seed)
 264 {
 265   /* Make it definitely odd.  */
 266   seed |= 1;
 267
 268   while (!is_prime (seed))
 269     seed += 2;
 270
 271   return seed;
 272 }
 273
 274
 275 static int
 276 is_prime (unsigned long int candidate)
 277 {
 278   /* No even number and none less than 10 will be passed here.  */
 279   unsigned long int divn = 3;
 280   unsigned long int sq = divn * divn;
 281
 282   while (sq < candidate && candidate % divn != 0)
 283     {
 284       ++divn;
 285       sq += 4 * divn;
 286       ++divn;
 287     }
 288
 289   return candidate % divn != 0;
 290 }