1/* Copyright (C) 1993-2020 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.
4
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.
9
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.
14
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 <https://www.gnu.org/licenses/>. */
18
19#include <errno.h>
20#include <malloc.h>
21#include <string.h>
22#include <stdint.h>
23#include <search.h>
24#include <limits.h>
25
26/* [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
27 [Knuth] The Art of Computer Programming, part 3 (6.4) */
28
29
30/* The reentrant version has no static variables to maintain the state.
31 Instead the interface of all functions is extended to take an argument
32 which describes the current status. */
33typedef struct _ENTRY
34{
35 unsigned int used;
36 ENTRY entry;
37}
38_ENTRY;
39
40
41/* For the used double hash method the table size has to be a prime. To
42 correct the user given table size we need a prime test. This trivial
43 algorithm is adequate because
44 a) the code is (most probably) called a few times per program run and
45 b) the number is small because the table must fit in the core */
46static int
47isprime (unsigned int number)
48{
49 /* no even number will be passed */
50 for (unsigned int div = 3; div <= number / div; div += 2)
51 if (number % div == 0)
52 return 0;
53 return 1;
54}
55
56/* Before using the hash table we must allocate memory for it.
57 Test for an existing table are done. We allocate one element
58 more as the found prime number says. This is done for more effective
59 indexing as explained in the comment for the hsearch function.
60 The contents of the table is zeroed, especially the field used
61 becomes zero. */
62int
63__hcreate_r (size_t nel, struct hsearch_data *htab)
64{
65 /* Test for correct arguments. */
66 if (htab == NULL)
67 {
68 __set_errno (EINVAL);
69 return 0;
70 }
71
72 /* There is still another table active. Return with error. */
73 if (htab->table != NULL)
74 return 0;
75
76 /* We need a size of at least 3. Otherwise the hash functions we
77 use will not work. */
78 if (nel < 3)
79 nel = 3;
80
81 /* Change nel to the first prime number in the range [nel, UINT_MAX - 2],
82 The '- 2' means 'nel += 2' cannot overflow. */
83 for (nel |= 1; ; nel += 2)
84 {
85 if (UINT_MAX - 2 < nel)
86 {
87 __set_errno (ENOMEM);
88 return 0;
89 }
90 if (isprime (nel))
91 break;
92 }
93
94 htab->size = nel;
95 htab->filled = 0;
96
97 /* allocate memory and zero out */
98 htab->table = (_ENTRY *) calloc (htab->size + 1, sizeof (_ENTRY));
99 if (htab->table == NULL)
100 return 0;
101
102 /* everything went alright */
103 return 1;
104}
105libc_hidden_def (__hcreate_r)
106weak_alias (__hcreate_r, hcreate_r)
107
108
109/* After using the hash table it has to be destroyed. The used memory can
110 be freed and the local static variable can be marked as not used. */
111void
112__hdestroy_r (struct hsearch_data *htab)
113{
114 /* Test for correct arguments. */
115 if (htab == NULL)
116 {
117 __set_errno (EINVAL);
118 return;
119 }
120
121 /* Free used memory. */
122 free (htab->table);
123
124 /* the sign for an existing table is an value != NULL in htable */
125 htab->table = NULL;
126}
127libc_hidden_def (__hdestroy_r)
128weak_alias (__hdestroy_r, hdestroy_r)
129
130
131/* This is the search function. It uses double hashing with open addressing.
132 The argument item.key has to be a pointer to an zero terminated, most
133 probably strings of chars. The function for generating a number of the
134 strings is simple but fast. It can be replaced by a more complex function
135 like ajw (see [Aho,Sethi,Ullman]) if the needs are shown.
136
137 We use an trick to speed up the lookup. The table is created by hcreate
138 with one more element available. This enables us to use the index zero
139 special. This index will never be used because we store the first hash
140 index in the field used where zero means not used. Every other value
141 means used. The used field can be used as a first fast comparison for
142 equality of the stored and the parameter value. This helps to prevent
143 unnecessary expensive calls of strcmp. */
144int
145__hsearch_r (ENTRY item, ACTION action, ENTRY **retval,
146 struct hsearch_data *htab)
147{
148 unsigned int hval;
149 unsigned int count;
150 unsigned int len = strlen (item.key);
151 unsigned int idx;
152
153 /* Compute an value for the given string. Perhaps use a better method. */
154 hval = len;
155 count = len;
156 while (count-- > 0)
157 {
158 hval <<= 4;
159 hval += item.key[count];
160 }
161 if (hval == 0)
162 ++hval;
163
164 /* First hash function: simply take the modul but prevent zero. */
165 idx = hval % htab->size + 1;
166
167 if (htab->table[idx].used)
168 {
169 /* Further action might be required according to the action value. */
170 if (htab->table[idx].used == hval
171 && strcmp (item.key, htab->table[idx].entry.key) == 0)
172 {
173 *retval = &htab->table[idx].entry;
174 return 1;
175 }
176
177 /* Second hash function, as suggested in [Knuth] */
178 unsigned int hval2 = 1 + hval % (htab->size - 2);
179 unsigned int first_idx = idx;
180
181 do
182 {
183 /* Because SIZE is prime this guarantees to step through all
184 available indeces. */
185 if (idx <= hval2)
186 idx = htab->size + idx - hval2;
187 else
188 idx -= hval2;
189
190 /* If we visited all entries leave the loop unsuccessfully. */
191 if (idx == first_idx)
192 break;
193
194 /* If entry is found use it. */
195 if (htab->table[idx].used == hval
196 && strcmp (item.key, htab->table[idx].entry.key) == 0)
197 {
198 *retval = &htab->table[idx].entry;
199 return 1;
200 }
201 }
202 while (htab->table[idx].used);
203 }
204
205 /* An empty bucket has been found. */
206 if (action == ENTER)
207 {
208 /* If table is full and another entry should be entered return
209 with error. */
210 if (htab->filled == htab->size)
211 {
212 __set_errno (ENOMEM);
213 *retval = NULL;
214 return 0;
215 }
216
217 htab->table[idx].used = hval;
218 htab->table[idx].entry = item;
219
220 ++htab->filled;
221
222 *retval = &htab->table[idx].entry;
223 return 1;
224 }
225
226 __set_errno (ESRCH);
227 *retval = NULL;
228 return 0;
229}
230libc_hidden_def (__hsearch_r)
231weak_alias (__hsearch_r, hsearch_r)
232