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b168057a | 1 | /* Copyright (C) 1993-2015 Free Software Foundation, Inc. |
2c6fe0bd | 2 | This file is part of the GNU C Library. |
2604afb1 | 3 | Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, 1993. |
60478656 | 4 | |
2c6fe0bd | 5 | The GNU C Library is free software; you can redistribute it and/or |
41bdb6e2 AJ |
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. | |
60478656 | 9 | |
2c6fe0bd UD |
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 | |
41bdb6e2 | 13 | Lesser General Public License for more details. |
60478656 | 14 | |
41bdb6e2 | 15 | You should have received a copy of the GNU Lesser General Public |
59ba27a6 PE |
16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ | |
60478656 RM |
18 | |
19 | #include <errno.h> | |
20 | #include <malloc.h> | |
21 | #include <string.h> | |
22 | ||
23 | #include <search.h> | |
24 | ||
25 | /* [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986 | |
26 | [Knuth] The Art of Computer Programming, part 3 (6.4) */ | |
27 | ||
28 | ||
845dcb57 | 29 | /* The reentrant version has no static variables to maintain the state. |
60478656 RM |
30 | Instead the interface of all functions is extended to take an argument |
31 | which describes the current status. */ | |
32 | typedef struct _ENTRY | |
bbed653c | 33 | { |
d68171ed | 34 | unsigned int used; |
60478656 RM |
35 | ENTRY entry; |
36 | } | |
37 | _ENTRY; | |
38 | ||
39 | ||
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 */ | |
45 | static int | |
bbed653c | 46 | isprime (unsigned int number) |
60478656 RM |
47 | { |
48 | /* no even number will be passed */ | |
49 | unsigned int div = 3; | |
50 | ||
51 | while (div * div < number && number % div != 0) | |
52 | div += 2; | |
53 | ||
54 | return number % div != 0; | |
55 | } | |
56 | ||
57 | ||
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. | |
bbed653c | 62 | The contents of the table is zeroed, especially the field used |
60478656 RM |
63 | becomes zero. */ |
64 | int | |
65 | hcreate_r (nel, htab) | |
2c6fe0bd | 66 | size_t nel; |
60478656 RM |
67 | struct hsearch_data *htab; |
68 | { | |
69 | /* Test for correct arguments. */ | |
70 | if (htab == NULL) | |
71 | { | |
c4029823 | 72 | __set_errno (EINVAL); |
60478656 RM |
73 | return 0; |
74 | } | |
75 | ||
76 | /* There is still another table active. Return with error. */ | |
77 | if (htab->table != NULL) | |
78 | return 0; | |
79 | ||
8073a494 UD |
80 | /* We need a size of at least 3. Otherwise the hash functions we |
81 | use will not work. */ | |
82 | if (nel < 3) | |
83 | nel = 3; | |
60478656 RM |
84 | /* Change nel to the first prime number not smaller as nel. */ |
85 | nel |= 1; /* make odd */ | |
86 | while (!isprime (nel)) | |
87 | nel += 2; | |
88 | ||
89 | htab->size = nel; | |
90 | htab->filled = 0; | |
91 | ||
92 | /* allocate memory and zero out */ | |
93 | htab->table = (_ENTRY *) calloc (htab->size + 1, sizeof (_ENTRY)); | |
94 | if (htab->table == NULL) | |
95 | return 0; | |
96 | ||
97 | /* everything went alright */ | |
98 | return 1; | |
99 | } | |
a14f26ef | 100 | libc_hidden_def (hcreate_r) |
60478656 RM |
101 | |
102 | ||
103 | /* After using the hash table it has to be destroyed. The used memory can | |
104 | be freed and the local static variable can be marked as not used. */ | |
105 | void | |
106 | hdestroy_r (htab) | |
107 | struct hsearch_data *htab; | |
108 | { | |
109 | /* Test for correct arguments. */ | |
110 | if (htab == NULL) | |
111 | { | |
c4029823 | 112 | __set_errno (EINVAL); |
60478656 RM |
113 | return; |
114 | } | |
115 | ||
ee314200 UD |
116 | /* Free used memory. */ |
117 | free (htab->table); | |
60478656 | 118 | |
bbed653c | 119 | /* the sign for an existing table is an value != NULL in htable */ |
60478656 RM |
120 | htab->table = NULL; |
121 | } | |
a14f26ef | 122 | libc_hidden_def (hdestroy_r) |
60478656 RM |
123 | |
124 | ||
6d52618b | 125 | /* This is the search function. It uses double hashing with open addressing. |
60478656 RM |
126 | The argument item.key has to be a pointer to an zero terminated, most |
127 | probably strings of chars. The function for generating a number of the | |
128 | strings is simple but fast. It can be replaced by a more complex function | |
129 | like ajw (see [Aho,Sethi,Ullman]) if the needs are shown. | |
bbed653c | 130 | |
60478656 RM |
131 | We use an trick to speed up the lookup. The table is created by hcreate |
132 | with one more element available. This enables us to use the index zero | |
133 | special. This index will never be used because we store the first hash | |
134 | index in the field used where zero means not used. Every other value | |
135 | means used. The used field can be used as a first fast comparison for | |
136 | equality of the stored and the parameter value. This helps to prevent | |
137 | unnecessary expensive calls of strcmp. */ | |
138 | int | |
139 | hsearch_r (item, action, retval, htab) | |
140 | ENTRY item; | |
141 | ACTION action; | |
142 | ENTRY **retval; | |
143 | struct hsearch_data *htab; | |
144 | { | |
145 | unsigned int hval; | |
146 | unsigned int count; | |
147 | unsigned int len = strlen (item.key); | |
148 | unsigned int idx; | |
149 | ||
60478656 RM |
150 | /* Compute an value for the given string. Perhaps use a better method. */ |
151 | hval = len; | |
152 | count = len; | |
153 | while (count-- > 0) | |
154 | { | |
155 | hval <<= 4; | |
156 | hval += item.key[count]; | |
157 | } | |
c2d5bd5b UD |
158 | if (hval == 0) |
159 | ++hval; | |
60478656 RM |
160 | |
161 | /* First hash function: simply take the modul but prevent zero. */ | |
64647f9a | 162 | idx = hval % htab->size + 1; |
60478656 RM |
163 | |
164 | if (htab->table[idx].used) | |
165 | { | |
166 | /* Further action might be required according to the action value. */ | |
60478656 RM |
167 | if (htab->table[idx].used == hval |
168 | && strcmp (item.key, htab->table[idx].entry.key) == 0) | |
169 | { | |
60478656 RM |
170 | *retval = &htab->table[idx].entry; |
171 | return 1; | |
172 | } | |
173 | ||
174 | /* Second hash function, as suggested in [Knuth] */ | |
64647f9a UD |
175 | unsigned int hval2 = 1 + hval % (htab->size - 2); |
176 | unsigned int first_idx = idx; | |
bbed653c | 177 | |
60478656 RM |
178 | do |
179 | { | |
180 | /* Because SIZE is prime this guarantees to step through all | |
181 | available indeces. */ | |
182 | if (idx <= hval2) | |
183 | idx = htab->size + idx - hval2; | |
184 | else | |
185 | idx -= hval2; | |
186 | ||
6973fc01 | 187 | /* If we visited all entries leave the loop unsuccessfully. */ |
64647f9a | 188 | if (idx == first_idx) |
6973fc01 UD |
189 | break; |
190 | ||
60478656 RM |
191 | /* If entry is found use it. */ |
192 | if (htab->table[idx].used == hval | |
193 | && strcmp (item.key, htab->table[idx].entry.key) == 0) | |
194 | { | |
60478656 RM |
195 | *retval = &htab->table[idx].entry; |
196 | return 1; | |
197 | } | |
198 | } | |
199 | while (htab->table[idx].used); | |
200 | } | |
201 | ||
202 | /* An empty bucket has been found. */ | |
203 | if (action == ENTER) | |
204 | { | |
2604afb1 UD |
205 | /* If table is full and another entry should be entered return |
206 | with error. */ | |
71b8b018 | 207 | if (htab->filled == htab->size) |
2604afb1 UD |
208 | { |
209 | __set_errno (ENOMEM); | |
210 | *retval = NULL; | |
211 | return 0; | |
212 | } | |
213 | ||
60478656 RM |
214 | htab->table[idx].used = hval; |
215 | htab->table[idx].entry = item; | |
216 | ||
217 | ++htab->filled; | |
218 | ||
219 | *retval = &htab->table[idx].entry; | |
220 | return 1; | |
221 | } | |
222 | ||
c4029823 | 223 | __set_errno (ESRCH); |
60478656 RM |
224 | *retval = NULL; |
225 | return 0; | |
226 | } | |
509d1b68 | 227 | libc_hidden_def (hsearch_r) |