1 /*-
2 * Copyright (c) 2015 Nuxi, https://nuxi.nl/
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23 * SUCH DAMAGE.
24 */
25
26 #include <sys/cdefs.h>
27 __FBSDID("$FreeBSD: head/lib/libc/stdlib/hsearch_r.c 292767 2015-12-27 07:50:11Z ed $");
28
29 #include <errno.h>
30 #include <limits.h>
31 #include <search.h>
32 #include <stdint.h>
33 #include <stdlib.h>
34 #include <string.h>
35
36 #include "hsearch.h"
37
38 /*
39 * Look up an unused entry in the hash table for a given hash. For this
40 * implementation we use quadratic probing. Quadratic probing has the
41 * advantage of preventing primary clustering.
42 */
43 static ENTRY *
hsearch_lookup_free(struct __hsearch * hsearch,size_t hash)44 hsearch_lookup_free(struct __hsearch *hsearch, size_t hash)
45 {
46 size_t index, i;
47
48 for (index = hash, i = 0;; index += ++i) {
49 ENTRY *entry = &hsearch->entries[index & hsearch->index_mask];
50 if (entry->key == NULL)
51 return (entry);
52 }
53 }
54
55 /*
56 * Computes an FNV-1a hash of the key. Depending on the pointer size, this
57 * either uses the 32- or 64-bit FNV prime.
58 */
59 static size_t
hsearch_hash(size_t offset_basis,const char * str)60 hsearch_hash(size_t offset_basis, const char *str)
61 {
62 size_t hash;
63
64 hash = offset_basis;
65 while (*str != '\0') {
66 hash ^= (uint8_t)*str++;
67 if (sizeof(size_t) * CHAR_BIT <= 32)
68 hash *= UINT32_C(16777619);
69 else
70 hash *= UINT64_C(1099511628211);
71 }
72 return (hash);
73 }
74
75 int
hsearch_r(ENTRY item,ACTION action,ENTRY ** retval,struct hsearch_data * htab)76 hsearch_r(ENTRY item, ACTION action, ENTRY **retval, struct hsearch_data *htab)
77 {
78 struct __hsearch *hsearch;
79 ENTRY *entry, *old_entries, *new_entries;
80 size_t hash, index, i, old_hash, old_count, new_count;
81
82 hsearch = htab->__hsearch;
83 hash = hsearch_hash(hsearch->offset_basis, item.key);
84
85 /*
86 * Search the hash table for an existing entry for this key.
87 * Stop searching if we run into an unused hash table entry.
88 */
89 for (index = hash, i = 0;; index += ++i) {
90 entry = &hsearch->entries[index & hsearch->index_mask];
91 if (entry->key == NULL)
92 break;
93 if (strcmp(entry->key, item.key) == 0) {
94 *retval = entry;
95 return (1);
96 }
97 }
98
99 /* Only perform the insertion if action is set to ENTER. */
100 if (action == FIND) {
101 errno = ESRCH;
102 return (0);
103 }
104
105 if (hsearch->entries_used * 2 >= hsearch->index_mask) {
106 /* Preserve the old hash table entries. */
107 old_count = hsearch->index_mask + 1;
108 old_entries = hsearch->entries;
109
110 /*
111 * Allocate and install a new table if insertion would
112 * yield a hash table that is more than 50% used. By
113 * using 50% as a threshold, a lookup will only take up
114 * to two steps on average.
115 */
116 new_count = (hsearch->index_mask + 1) * 2;
117 new_entries = calloc(new_count, sizeof(ENTRY));
118 if (new_entries == NULL)
119 return (0);
120 hsearch->entries = new_entries;
121 hsearch->index_mask = new_count - 1;
122
123 /* Copy over the entries from the old table to the new table. */
124 for (i = 0; i < old_count; ++i) {
125 entry = &old_entries[i];
126 if (entry->key != NULL) {
127 old_hash = hsearch_hash(hsearch->offset_basis,
128 entry->key);
129 *hsearch_lookup_free(hsearch, old_hash) =
130 *entry;
131 }
132 }
133
134 /* Destroy the old hash table entries. */
135 free(old_entries);
136
137 /*
138 * Perform a new lookup for a free table entry, so that
139 * we insert the entry into the new hash table.
140 */
141 hsearch = htab->__hsearch;
142 entry = hsearch_lookup_free(hsearch, hash);
143 }
144
145 /* Insert the new entry into the hash table. */
146 *entry = item;
147 ++hsearch->entries_used;
148 *retval = entry;
149 return (1);
150 }
151