1 /* Copyright (C) 1993-2015 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, 1993.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library 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 GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
25 /* [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
26 [Knuth] The Art of Computer Programming, part 3 (6.4) */
29 /* The reentrant version has no static variables to maintain the state.
30 Instead the interface of all functions is extended to take an argument
31 which describes the current status. */
40 /* For the used double hash method the table size has to be a prime. To
41 correct the user given table size we need a prime test. This trivial
42 algorithm is adequate because
43 a) the code is (most probably) called a few times per program run and
44 b) the number is small because the table must fit in the core */
46 isprime (unsigned int number
)
48 /* no even number will be passed */
51 while (div
* div
< number
&& number
% div
!= 0)
54 return number
% div
!= 0;
58 /* Before using the hash table we must allocate memory for it.
59 Test for an existing table are done. We allocate one element
60 more as the found prime number says. This is done for more effective
61 indexing as explained in the comment for the hsearch function.
62 The contents of the table is zeroed, especially the field used
65 __hcreate_r (nel
, htab
)
67 struct hsearch_data
*htab
;
69 /* Test for correct arguments. */
76 if (nel
>= SIZE_MAX
/ sizeof (_ENTRY
))
83 /* There is still another table active. Return with error. */
84 if (htab
->table
!= NULL
)
87 /* We need a size of at least 3. Otherwise the hash functions we
91 /* Change nel to the first prime number not smaller as nel. */
92 nel
|= 1; /* make odd */
93 while (!isprime (nel
))
99 /* allocate memory and zero out */
100 htab
->table
= (_ENTRY
*) calloc (htab
->size
+ 1, sizeof (_ENTRY
));
101 if (htab
->table
== NULL
)
104 /* everything went alright */
107 libc_hidden_def (__hcreate_r
)
108 weak_alias (__hcreate_r
, hcreate_r
)
111 /* After using the hash table it has to be destroyed. The used memory can
112 be freed and the local static variable can be marked as not used. */
115 struct hsearch_data
*htab
;
117 /* Test for correct arguments. */
120 __set_errno (EINVAL
);
124 /* Free used memory. */
127 /* the sign for an existing table is an value != NULL in htable */
130 libc_hidden_def (__hdestroy_r
)
131 weak_alias (__hdestroy_r
, hdestroy_r
)
134 /* This is the search function. It uses double hashing with open addressing.
135 The argument item.key has to be a pointer to an zero terminated, most
136 probably strings of chars. The function for generating a number of the
137 strings is simple but fast. It can be replaced by a more complex function
138 like ajw (see [Aho,Sethi,Ullman]) if the needs are shown.
140 We use an trick to speed up the lookup. The table is created by hcreate
141 with one more element available. This enables us to use the index zero
142 special. This index will never be used because we store the first hash
143 index in the field used where zero means not used. Every other value
144 means used. The used field can be used as a first fast comparison for
145 equality of the stored and the parameter value. This helps to prevent
146 unnecessary expensive calls of strcmp. */
148 __hsearch_r (item
, action
, retval
, htab
)
152 struct hsearch_data
*htab
;
156 unsigned int len
= strlen (item
.key
);
159 /* Compute an value for the given string. Perhaps use a better method. */
165 hval
+= item
.key
[count
];
170 /* First hash function: simply take the modul but prevent zero. */
171 idx
= hval
% htab
->size
+ 1;
173 if (htab
->table
[idx
].used
)
175 /* Further action might be required according to the action value. */
176 if (htab
->table
[idx
].used
== hval
177 && strcmp (item
.key
, htab
->table
[idx
].entry
.key
) == 0)
179 *retval
= &htab
->table
[idx
].entry
;
183 /* Second hash function, as suggested in [Knuth] */
184 unsigned int hval2
= 1 + hval
% (htab
->size
- 2);
185 unsigned int first_idx
= idx
;
189 /* Because SIZE is prime this guarantees to step through all
190 available indeces. */
192 idx
= htab
->size
+ idx
- hval2
;
196 /* If we visited all entries leave the loop unsuccessfully. */
197 if (idx
== first_idx
)
200 /* If entry is found use it. */
201 if (htab
->table
[idx
].used
== hval
202 && strcmp (item
.key
, htab
->table
[idx
].entry
.key
) == 0)
204 *retval
= &htab
->table
[idx
].entry
;
208 while (htab
->table
[idx
].used
);
211 /* An empty bucket has been found. */
214 /* If table is full and another entry should be entered return
216 if (htab
->filled
== htab
->size
)
218 __set_errno (ENOMEM
);
223 htab
->table
[idx
].used
= hval
;
224 htab
->table
[idx
].entry
= item
;
228 *retval
= &htab
->table
[idx
].entry
;
236 libc_hidden_def (__hsearch_r
)
237 weak_alias (__hsearch_r
, hsearch_r
)