291 lines
6.6 KiB
C
291 lines
6.6 KiB
C
/* Implement simple hashing table with string based keys.
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Copyright (C) 1994-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published
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by the Free Software Foundation; version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, see <https://www.gnu.org/licenses/>. */
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#ifdef HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include <inttypes.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdint.h>
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#include <sys/types.h>
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#include <obstack.h>
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#ifdef HAVE_VALUES_H
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# include <values.h>
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#endif
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#include "simple-hash.h"
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#define obstack_chunk_alloc malloc
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#define obstack_chunk_free free
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#ifndef BITSPERBYTE
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# define BITSPERBYTE 8
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#endif
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#define hashval_t uint32_t
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#include "hashval.h"
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#include <programs/xmalloc.h>
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typedef struct hash_entry
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{
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unsigned long used;
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const void *key;
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size_t keylen;
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void *data;
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struct hash_entry *next;
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}
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hash_entry;
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/* Prototypes for local functions. */
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static void insert_entry_2 (hash_table *htab, const void *key, size_t keylen,
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unsigned long hval, size_t idx, void *data);
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static size_t lookup (const hash_table *htab, const void *key, size_t keylen,
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unsigned long int hval);
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static int is_prime (unsigned long int candidate);
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int
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init_hash (hash_table *htab, unsigned long int init_size)
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{
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/* We need the size to be a prime. */
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init_size = next_prime (init_size);
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/* Initialize the data structure. */
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htab->size = init_size;
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htab->filled = 0;
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htab->first = NULL;
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htab->table = (void *) xcalloc (init_size + 1, sizeof (hash_entry));
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if (htab->table == NULL)
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return -1;
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obstack_init (&htab->mem_pool);
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return 0;
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}
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int
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delete_hash (hash_table *htab)
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{
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free (htab->table);
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obstack_free (&htab->mem_pool, NULL);
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return 0;
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}
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int
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insert_entry (hash_table *htab, const void *key, size_t keylen, void *data)
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{
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unsigned long int hval = compute_hashval (key, keylen);
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hash_entry *table = (hash_entry *) htab->table;
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size_t idx = lookup (htab, key, keylen, hval);
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if (table[idx].used)
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/* We don't want to overwrite the old value. */
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return -1;
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else
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{
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/* An empty bucket has been found. */
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insert_entry_2 (htab, obstack_copy (&htab->mem_pool, key, keylen),
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keylen, hval, idx, data);
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return 0;
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}
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}
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static void
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insert_entry_2 (hash_table *htab, const void *key, size_t keylen,
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unsigned long int hval, size_t idx, void *data)
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{
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hash_entry *table = (hash_entry *) htab->table;
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table[idx].used = hval;
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table[idx].key = key;
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table[idx].keylen = keylen;
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table[idx].data = data;
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/* List the new value in the list. */
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if ((hash_entry *) htab->first == NULL)
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{
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table[idx].next = &table[idx];
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htab->first = &table[idx];
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}
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else
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{
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table[idx].next = ((hash_entry *) htab->first)->next;
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((hash_entry *) htab->first)->next = &table[idx];
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htab->first = &table[idx];
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}
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++htab->filled;
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if (100 * htab->filled > 75 * htab->size)
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{
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/* Table is filled more than 75%. Resize the table.
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Experiments have shown that for best performance, this threshold
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must lie between 40% and 85%. */
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unsigned long int old_size = htab->size;
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htab->size = next_prime (htab->size * 2);
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htab->filled = 0;
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htab->first = NULL;
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htab->table = (void *) xcalloc (1 + htab->size, sizeof (hash_entry));
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for (idx = 1; idx <= old_size; ++idx)
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if (table[idx].used)
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insert_entry_2 (htab, table[idx].key, table[idx].keylen,
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table[idx].used,
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lookup (htab, table[idx].key, table[idx].keylen,
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table[idx].used),
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table[idx].data);
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free (table);
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}
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}
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int
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find_entry (const hash_table *htab, const void *key, size_t keylen,
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void **result)
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{
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hash_entry *table = (hash_entry *) htab->table;
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size_t idx = lookup (htab, key, keylen, compute_hashval (key, keylen));
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if (table[idx].used == 0)
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return -1;
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*result = table[idx].data;
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return 0;
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}
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int
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set_entry (hash_table *htab, const void *key, size_t keylen, void *newval)
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{
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hash_entry *table = (hash_entry *) htab->table;
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size_t idx = lookup (htab, key, keylen, compute_hashval (key, keylen));
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if (table[idx].used == 0)
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return -1;
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table[idx].data = newval;
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return 0;
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}
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int
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iterate_table (const hash_table *htab, void **ptr, const void **key,
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size_t *keylen, void **data)
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{
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if (*ptr == NULL)
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{
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if (htab->first == NULL)
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return -1;
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*ptr = (void *) ((hash_entry *) htab->first)->next;
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}
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else
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{
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if (*ptr == htab->first)
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return -1;
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*ptr = (void *) (((hash_entry *) *ptr)->next);
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}
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*key = ((hash_entry *) *ptr)->key;
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*keylen = ((hash_entry *) *ptr)->keylen;
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*data = ((hash_entry *) *ptr)->data;
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return 0;
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}
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/* References:
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[Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
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[Knuth] The Art of Computer Programming, part3 (6.4) */
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static size_t
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lookup (const hash_table *htab, const void *key, size_t keylen,
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unsigned long int hval)
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{
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unsigned long int hash;
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size_t idx;
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hash_entry *table = (hash_entry *) htab->table;
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/* First hash function: simply take the modul but prevent zero. */
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hash = 1 + hval % htab->size;
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idx = hash;
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if (table[idx].used)
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{
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if (table[idx].used == hval && table[idx].keylen == keylen
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&& memcmp (table[idx].key, key, keylen) == 0)
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return idx;
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/* Second hash function as suggested in [Knuth]. */
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hash = 1 + hval % (htab->size - 2);
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do
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{
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if (idx <= hash)
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idx = htab->size + idx - hash;
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else
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idx -= hash;
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/* If entry is found use it. */
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if (table[idx].used == hval && table[idx].keylen == keylen
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&& memcmp (table[idx].key, key, keylen) == 0)
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return idx;
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}
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while (table[idx].used);
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}
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return idx;
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}
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unsigned long int
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next_prime (unsigned long int seed)
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{
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/* Make it definitely odd. */
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seed |= 1;
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while (!is_prime (seed))
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seed += 2;
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return seed;
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}
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static int
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is_prime (unsigned long int candidate)
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{
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/* No even number and none less than 10 will be passed here. */
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unsigned long int divn = 3;
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unsigned long int sq = divn * divn;
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while (sq < candidate && candidate % divn != 0)
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{
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++divn;
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sq += 4 * divn;
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++divn;
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}
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return candidate % divn != 0;
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}
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