glibc/locale/programs/simple-hash.c

354 lines
8.0 KiB
C

/* Implement simple hashing table with string based keys.
Copyright (C) 1994-1997, 2000, 2001 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, October 1994.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#if HAVE_OBSTACK
# include <obstack.h>
#else
# include "obstack.h"
#endif
#ifdef HAVE_VALUES_H
# include <values.h>
#endif
#include "simple-hash.h"
#define obstack_chunk_alloc malloc
#define obstack_chunk_free free
#ifndef BITSPERBYTE
# define BITSPERBYTE 8
#endif
#ifndef LONGBITS
# define LONGBITS (sizeof (long) * BITSPERBYTE)
#endif
#ifndef bcopy
# define bcopy(s, d, n) memcpy ((d), (s), (n))
#endif
extern void *xmalloc (size_t __n);
extern void *xcalloc (size_t __n, size_t __m);
typedef struct hash_entry
{
unsigned long used;
const void *key;
size_t keylen;
void *data;
struct hash_entry *next;
}
hash_entry;
/* Prototypes for local functions. */
static void insert_entry_2 (hash_table *htab, const void *key, size_t keylen,
unsigned long hval, size_t idx, void *data);
static size_t lookup (const hash_table *htab, const void *key, size_t keylen,
unsigned long int hval);
static unsigned long compute_hashval (const void *key, size_t keylen);
static int is_prime (unsigned long int candidate);
int
init_hash (htab, init_size)
hash_table *htab;
unsigned long int init_size;
{
/* We need the size to be a prime. */
init_size = next_prime (init_size);
/* Initialize the data structure. */
htab->size = init_size;
htab->filled = 0;
htab->first = NULL;
htab->table = (void *) xcalloc (init_size + 1, sizeof (hash_entry));
if (htab->table == NULL)
return -1;
obstack_init (&htab->mem_pool);
return 0;
}
int
delete_hash (htab)
hash_table *htab;
{
free (htab->table);
obstack_free (&htab->mem_pool, NULL);
return 0;
}
int
insert_entry (htab, key, keylen, data)
hash_table *htab;
const void *key;
size_t keylen;
void *data;
{
unsigned long int hval = compute_hashval (key, keylen);
hash_entry *table = (hash_entry *) htab->table;
size_t idx = lookup (htab, key, keylen, hval);
if (table[idx].used)
/* We don't want to overwrite the old value. */
return -1;
else
{
/* An empty bucket has been found. */
insert_entry_2 (htab, obstack_copy (&htab->mem_pool, key, keylen),
keylen, hval, idx, data);
return 0;
}
}
static void
insert_entry_2 (htab, key, keylen, hval, idx, data)
hash_table *htab;
const void *key;
size_t keylen;
unsigned long int hval;
size_t idx;
void *data;
{
hash_entry *table = (hash_entry *) htab->table;
table[idx].used = hval;
table[idx].key = key;
table[idx].keylen = keylen;
table[idx].data = data;
/* List the new value in the list. */
if ((hash_entry *) htab->first == NULL)
{
table[idx].next = &table[idx];
*(hash_entry **) &htab->first = &table[idx];
}
else
{
table[idx].next = ((hash_entry *) htab->first)->next;
((hash_entry *) htab->first)->next = &table[idx];
*(hash_entry **) &htab->first = &table[idx];
}
++htab->filled;
if (100 * htab->filled > 75 * htab->size)
{
/* Table is filled more than 75%. Resize the table.
Experiments have shown that for best performance, this threshold
must lie between 40% and 85%. */
unsigned long int old_size = htab->size;
htab->size = next_prime (htab->size * 2);
htab->filled = 0;
htab->first = NULL;
htab->table = (void *) xcalloc (1 + htab->size, sizeof (hash_entry));
for (idx = 1; idx <= old_size; ++idx)
if (table[idx].used)
insert_entry_2 (htab, table[idx].key, table[idx].keylen,
table[idx].used,
lookup (htab, table[idx].key, table[idx].keylen,
table[idx].used),
table[idx].data);
free (table);
}
}
int
find_entry (htab, key, keylen, result)
const hash_table *htab;
const void *key;
size_t keylen;
void **result;
{
hash_entry *table = (hash_entry *) htab->table;
size_t idx = lookup (htab, key, keylen, compute_hashval (key, keylen));
if (table[idx].used == 0)
return -1;
*result = table[idx].data;
return 0;
}
int
set_entry (htab, key, keylen, newval)
hash_table *htab;
const void *key;
size_t keylen;
void *newval;
{
hash_entry *table = (hash_entry *) htab->table;
size_t idx = lookup (htab, key, keylen, compute_hashval (key, keylen));
if (table[idx].used == 0)
return -1;
table[idx].data = newval;
return 0;
}
int
iterate_table (htab, ptr, key, keylen, data)
const hash_table *htab;
void **ptr;
const void **key;
size_t *keylen;
void **data;
{
if (*ptr == NULL)
{
if (htab->first == NULL)
return -1;
*ptr = (void *) ((hash_entry *) htab->first)->next;
}
else
{
if (*ptr == htab->first)
return -1;
*ptr = (void *) (((hash_entry *) *ptr)->next);
}
*key = ((hash_entry *) *ptr)->key;
*keylen = ((hash_entry *) *ptr)->keylen;
*data = ((hash_entry *) *ptr)->data;
return 0;
}
/* References:
[Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
[Knuth] The Art of Computer Programming, part3 (6.4) */
static size_t
lookup (htab, key, keylen, hval)
const hash_table *htab;
const void *key;
size_t keylen;
unsigned long int hval;
{
unsigned long int hash;
size_t idx;
hash_entry *table = (hash_entry *) htab->table;
/* First hash function: simply take the modul but prevent zero. */
hash = 1 + hval % htab->size;
idx = hash;
if (table[idx].used)
{
if (table[idx].used == hval && table[idx].keylen == keylen
&& memcmp (table[idx].key, key, keylen) == 0)
return idx;
/* Second hash function as suggested in [Knuth]. */
hash = 1 + hval % (htab->size - 2);
do
{
if (idx <= hash)
idx = htab->size + idx - hash;
else
idx -= hash;
/* If entry is found use it. */
if (table[idx].used == hval && table[idx].keylen == keylen
&& memcmp (table[idx].key, key, keylen) == 0)
return idx;
}
while (table[idx].used);
}
return idx;
}
static unsigned long
compute_hashval (key, keylen)
const void *key;
size_t keylen;
{
size_t cnt;
unsigned long int hval;
/* Compute the hash value for the given string. The algorithm
is taken from [Aho,Sethi,Ullman], modified to reduce the number of
collisions for short strings with very varied bit patterns.
See http://www.clisp.org/haible/hashfunc.html. */
cnt = 0;
hval = keylen;
while (cnt < keylen)
{
hval = (hval << 9) | (hval >> (LONGBITS - 9));
hval += (unsigned long int) *(((char *) key) + cnt++);
}
return hval != 0 ? hval : ~((unsigned long) 0);
}
unsigned long
next_prime (seed)
unsigned long int seed;
{
/* Make it definitely odd. */
seed |= 1;
while (!is_prime (seed))
seed += 2;
return seed;
}
static int
is_prime (candidate)
unsigned long int candidate;
{
/* No even number and none less than 10 will be passed here. */
unsigned long int divn = 3;
unsigned long int sq = divn * divn;
while (sq < candidate && candidate % divn != 0)
{
++divn;
sq += 4 * divn;
++divn;
}
return candidate % divn != 0;
}