+++ /dev/null
-/* Copyright (C) 1993, 1995, 1996, 1997 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, 1993.
-
- 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; see the file COPYING.LIB. If not,
- write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
- Boston, MA 02111-1307, USA. */
-
-#include <errno.h>
-#include <malloc.h>
-#include <string.h>
-
-#define __USE_GNU
-#ifndef __set_errno
-#define __set_errno(e) errno = (e)
-#endif
-#include <search.h>
-
-/* [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
- [Knuth] The Art of Computer Programming, part 3 (6.4) */
-
-
-/* The reentrant version has no static variables to maintain the state.
- Instead the interface of all functions is extended to take an argument
- which describes the current status. */
-typedef struct _ENTRY
-{
- unsigned int used;
- ENTRY entry;
-}
-_ENTRY;
-
-
-/* For the used double hash method the table size has to be a prime. To
- correct the user given table size we need a prime test. This trivial
- algorithm is adequate because
- a) the code is (most probably) called a few times per program run and
- b) the number is small because the table must fit in the core */
-static int
-isprime (unsigned int number)
-{
- /* no even number will be passed */
- unsigned int div = 3;
-
- while (div * div < number && number % div != 0)
- div += 2;
-
- return number % div != 0;
-}
-
-
-/* Before using the hash table we must allocate memory for it.
- Test for an existing table are done. We allocate one element
- more as the found prime number says. This is done for more effective
- indexing as explained in the comment for the hsearch function.
- The contents of the table is zeroed, especially the field used
- becomes zero. */
-int
-hcreate_r (nel, htab)
- size_t nel;
- struct hsearch_data *htab;
-{
- /* Test for correct arguments. */
- if (htab == NULL)
- {
- __set_errno (EINVAL);
- return 0;
- }
-
- /* There is still another table active. Return with error. */
- if (htab->table != NULL)
- return 0;
-
- /* Change nel to the first prime number not smaller as nel. */
- nel |= 1; /* make odd */
- while (!isprime (nel))
- nel += 2;
-
- htab->size = nel;
- htab->filled = 0;
-
- /* allocate memory and zero out */
- htab->table = (_ENTRY *) calloc (htab->size + 1, sizeof (_ENTRY));
- if (htab->table == NULL)
- return 0;
-
- /* everything went alright */
- return 1;
-}
-
-
-/* After using the hash table it has to be destroyed. The used memory can
- be freed and the local static variable can be marked as not used. */
-void
-hdestroy_r (htab)
- struct hsearch_data *htab;
-{
- /* Test for correct arguments. */
- if (htab == NULL)
- {
- __set_errno (EINVAL);
- return;
- }
-
- if (htab->table != NULL)
- /* free used memory */
- free (htab->table);
-
- /* the sign for an existing table is an value != NULL in htable */
- htab->table = NULL;
-}
-
-
-/* This is the search function. It uses double hashing with open addressing.
- The argument item.key has to be a pointer to an zero terminated, most
- probably strings of chars. The function for generating a number of the
- strings is simple but fast. It can be replaced by a more complex function
- like ajw (see [Aho,Sethi,Ullman]) if the needs are shown.
-
- We use an trick to speed up the lookup. The table is created by hcreate
- with one more element available. This enables us to use the index zero
- special. This index will never be used because we store the first hash
- index in the field used where zero means not used. Every other value
- means used. The used field can be used as a first fast comparison for
- equality of the stored and the parameter value. This helps to prevent
- unnecessary expensive calls of strcmp. */
-int
-hsearch_r (item, action, retval, htab)
- ENTRY item;
- ACTION action;
- ENTRY **retval;
- struct hsearch_data *htab;
-{
- unsigned int hval;
- unsigned int count;
- unsigned int len = strlen (item.key);
- unsigned int idx;
-
- /* Compute an value for the given string. Perhaps use a better method. */
- hval = len;
- count = len;
- while (count-- > 0)
- {
- hval <<= 4;
- hval += item.key[count];
- }
-
- /* First hash function: simply take the modulo but prevent zero. */
- hval %= htab->size;
- if (hval == 0)
- ++hval;
-
- /* The first index tried. */
- idx = hval;
-
- if (htab->table[idx].used)
- {
- /* Further action might be required according to the action value. */
- unsigned hval2;
-
- if (htab->table[idx].used == hval
- && strcmp (item.key, htab->table[idx].entry.key) == 0)
- {
- if (action == ENTER)
- htab->table[idx].entry.data = item.data;
-
- *retval = &htab->table[idx].entry;
- return 1;
- }
-
- /* Second hash function, as suggested in [Knuth] */
- hval2 = 1 + hval % (htab->size - 2);
-
- do
- {
- /* Because SIZE is prime this guarantees to step through all
- available indexes. */
- if (idx <= hval2)
- idx = htab->size + idx - hval2;
- else
- idx -= hval2;
-
- /* If we visited all entries leave the loop unsuccessfully. */
- if (idx == hval)
- break;
-
- /* If entry is found use it. */
- if (htab->table[idx].used == hval
- && strcmp (item.key, htab->table[idx].entry.key) == 0)
- {
- if (action == ENTER)
- htab->table[idx].entry.data = item.data;
-
- *retval = &htab->table[idx].entry;
- return 1;
- }
- }
- while (htab->table[idx].used);
- }
-
- /* An empty bucket has been found. */
- if (action == ENTER)
- {
- /* If table is full and another entry should be entered return
- with error. */
- if (action == ENTER && htab->filled == htab->size)
- {
- __set_errno (ENOMEM);
- *retval = NULL;
- return 0;
- }
-
- htab->table[idx].used = hval;
- htab->table[idx].entry = item;
-
- ++htab->filled;
-
- *retval = &htab->table[idx].entry;
- return 1;
- }
-
- __set_errno (ESRCH);
- *retval = NULL;
- return 0;
-}
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