hsearch_r.c revision 302408 
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: stable/11/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 */
43static ENTRY *
44hsearch_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 */
59static size_t
60hsearch_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
75int
76hsearch_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