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6d7e8eda | 1 | /* Copyright (C) 1993-2023 Free Software Foundation, Inc. |
2c6fe0bd | 2 | This file is part of the GNU C Library. |
60478656 | 3 | |
2c6fe0bd | 4 | The GNU C Library is free software; you can redistribute it and/or |
41bdb6e2 AJ |
5 | modify it under the terms of the GNU Lesser General Public |
6 | License as published by the Free Software Foundation; either | |
7 | version 2.1 of the License, or (at your option) any later version. | |
60478656 | 8 | |
2c6fe0bd UD |
9 | The GNU C Library is distributed in the hope that it will be useful, |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
41bdb6e2 | 12 | Lesser General Public License for more details. |
60478656 | 13 | |
41bdb6e2 | 14 | You should have received a copy of the GNU Lesser General Public |
59ba27a6 | 15 | License along with the GNU C Library; if not, see |
5a82c748 | 16 | <https://www.gnu.org/licenses/>. */ |
60478656 RM |
17 | |
18 | #include <errno.h> | |
19 | #include <malloc.h> | |
20 | #include <string.h> | |
2f5c1750 | 21 | #include <stdint.h> |
60478656 | 22 | #include <search.h> |
1d2a8245 | 23 | #include <limits.h> |
60478656 RM |
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 */ | |
bae7c7c7 FW |
49 | for (unsigned int div = 3; div <= number / div; div += 2) |
50 | if (number % div == 0) | |
51 | return 0; | |
52 | return 1; | |
60478656 RM |
53 | } |
54 | ||
60478656 RM |
55 | /* Before using the hash table we must allocate memory for it. |
56 | Test for an existing table are done. We allocate one element | |
57 | more as the found prime number says. This is done for more effective | |
58 | indexing as explained in the comment for the hsearch function. | |
bbed653c | 59 | The contents of the table is zeroed, especially the field used |
60478656 RM |
60 | becomes zero. */ |
61 | int | |
9d46370c | 62 | __hcreate_r (size_t nel, struct hsearch_data *htab) |
60478656 RM |
63 | { |
64 | /* Test for correct arguments. */ | |
65 | if (htab == NULL) | |
66 | { | |
c4029823 | 67 | __set_errno (EINVAL); |
60478656 RM |
68 | return 0; |
69 | } | |
70 | ||
71 | /* There is still another table active. Return with error. */ | |
72 | if (htab->table != NULL) | |
73 | return 0; | |
74 | ||
8073a494 UD |
75 | /* We need a size of at least 3. Otherwise the hash functions we |
76 | use will not work. */ | |
77 | if (nel < 3) | |
78 | nel = 3; | |
bae7c7c7 FW |
79 | |
80 | /* Change nel to the first prime number in the range [nel, UINT_MAX - 2], | |
81 | The '- 2' means 'nel += 2' cannot overflow. */ | |
82 | for (nel |= 1; ; nel += 2) | |
83 | { | |
84 | if (UINT_MAX - 2 < nel) | |
85 | { | |
86 | __set_errno (ENOMEM); | |
87 | return 0; | |
88 | } | |
89 | if (isprime (nel)) | |
90 | break; | |
91 | } | |
60478656 RM |
92 | |
93 | htab->size = nel; | |
94 | htab->filled = 0; | |
95 | ||
96 | /* allocate memory and zero out */ | |
97 | htab->table = (_ENTRY *) calloc (htab->size + 1, sizeof (_ENTRY)); | |
98 | if (htab->table == NULL) | |
99 | return 0; | |
100 | ||
101 | /* everything went alright */ | |
102 | return 1; | |
103 | } | |
4ffb1771 JM |
104 | libc_hidden_def (__hcreate_r) |
105 | weak_alias (__hcreate_r, hcreate_r) | |
60478656 RM |
106 | |
107 | ||
108 | /* After using the hash table it has to be destroyed. The used memory can | |
109 | be freed and the local static variable can be marked as not used. */ | |
110 | void | |
9d46370c | 111 | __hdestroy_r (struct hsearch_data *htab) |
60478656 RM |
112 | { |
113 | /* Test for correct arguments. */ | |
114 | if (htab == NULL) | |
115 | { | |
c4029823 | 116 | __set_errno (EINVAL); |
60478656 RM |
117 | return; |
118 | } | |
119 | ||
ee314200 UD |
120 | /* Free used memory. */ |
121 | free (htab->table); | |
60478656 | 122 | |
bbed653c | 123 | /* the sign for an existing table is an value != NULL in htable */ |
60478656 RM |
124 | htab->table = NULL; |
125 | } | |
4ffb1771 JM |
126 | libc_hidden_def (__hdestroy_r) |
127 | weak_alias (__hdestroy_r, hdestroy_r) | |
60478656 RM |
128 | |
129 | ||
6d52618b | 130 | /* This is the search function. It uses double hashing with open addressing. |
60478656 RM |
131 | The argument item.key has to be a pointer to an zero terminated, most |
132 | probably strings of chars. The function for generating a number of the | |
133 | strings is simple but fast. It can be replaced by a more complex function | |
134 | like ajw (see [Aho,Sethi,Ullman]) if the needs are shown. | |
bbed653c | 135 | |
60478656 RM |
136 | We use an trick to speed up the lookup. The table is created by hcreate |
137 | with one more element available. This enables us to use the index zero | |
138 | special. This index will never be used because we store the first hash | |
139 | index in the field used where zero means not used. Every other value | |
140 | means used. The used field can be used as a first fast comparison for | |
141 | equality of the stored and the parameter value. This helps to prevent | |
142 | unnecessary expensive calls of strcmp. */ | |
143 | int | |
f63f2bfd JM |
144 | __hsearch_r (ENTRY item, ACTION action, ENTRY **retval, |
145 | struct hsearch_data *htab) | |
60478656 RM |
146 | { |
147 | unsigned int hval; | |
148 | unsigned int count; | |
149 | unsigned int len = strlen (item.key); | |
150 | unsigned int idx; | |
151 | ||
60478656 RM |
152 | /* Compute an value for the given string. Perhaps use a better method. */ |
153 | hval = len; | |
154 | count = len; | |
155 | while (count-- > 0) | |
156 | { | |
157 | hval <<= 4; | |
158 | hval += item.key[count]; | |
159 | } | |
c2d5bd5b UD |
160 | if (hval == 0) |
161 | ++hval; | |
60478656 RM |
162 | |
163 | /* First hash function: simply take the modul but prevent zero. */ | |
64647f9a | 164 | idx = hval % htab->size + 1; |
60478656 RM |
165 | |
166 | if (htab->table[idx].used) | |
167 | { | |
168 | /* Further action might be required according to the action value. */ | |
60478656 RM |
169 | if (htab->table[idx].used == hval |
170 | && strcmp (item.key, htab->table[idx].entry.key) == 0) | |
171 | { | |
60478656 RM |
172 | *retval = &htab->table[idx].entry; |
173 | return 1; | |
174 | } | |
175 | ||
176 | /* Second hash function, as suggested in [Knuth] */ | |
64647f9a UD |
177 | unsigned int hval2 = 1 + hval % (htab->size - 2); |
178 | unsigned int first_idx = idx; | |
bbed653c | 179 | |
60478656 RM |
180 | do |
181 | { | |
182 | /* Because SIZE is prime this guarantees to step through all | |
14ef9c18 | 183 | available indices. */ |
60478656 RM |
184 | if (idx <= hval2) |
185 | idx = htab->size + idx - hval2; | |
186 | else | |
187 | idx -= hval2; | |
188 | ||
6973fc01 | 189 | /* If we visited all entries leave the loop unsuccessfully. */ |
64647f9a | 190 | if (idx == first_idx) |
6973fc01 UD |
191 | break; |
192 | ||
60478656 RM |
193 | /* If entry is found use it. */ |
194 | if (htab->table[idx].used == hval | |
195 | && strcmp (item.key, htab->table[idx].entry.key) == 0) | |
196 | { | |
60478656 RM |
197 | *retval = &htab->table[idx].entry; |
198 | return 1; | |
199 | } | |
200 | } | |
201 | while (htab->table[idx].used); | |
202 | } | |
203 | ||
204 | /* An empty bucket has been found. */ | |
205 | if (action == ENTER) | |
206 | { | |
2604afb1 UD |
207 | /* If table is full and another entry should be entered return |
208 | with error. */ | |
71b8b018 | 209 | if (htab->filled == htab->size) |
2604afb1 UD |
210 | { |
211 | __set_errno (ENOMEM); | |
212 | *retval = NULL; | |
213 | return 0; | |
214 | } | |
215 | ||
60478656 RM |
216 | htab->table[idx].used = hval; |
217 | htab->table[idx].entry = item; | |
218 | ||
219 | ++htab->filled; | |
220 | ||
221 | *retval = &htab->table[idx].entry; | |
222 | return 1; | |
223 | } | |
224 | ||
c4029823 | 225 | __set_errno (ESRCH); |
60478656 RM |
226 | *retval = NULL; |
227 | return 0; | |
228 | } | |
4ffb1771 JM |
229 | libc_hidden_def (__hsearch_r) |
230 | weak_alias (__hsearch_r, hsearch_r) |