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 <errno.h>
27#include <limits.h>
28#include <search.h>
29#include <stdint.h>
30#include <stdlib.h>
31#include <string.h>
32
33#include "hsearch.h"
34
35/*
36 * Look up an unused entry in the hash table for a given hash. For this
37 * implementation we use quadratic probing. Quadratic probing has the
38 * advantage of preventing primary clustering.
39 */
40static ENTRY *
41hsearch_lookup_free(struct __hsearch *hsearch, size_t hash)
42{
43	size_t index, i;
44
45	for (index = hash, i = 0;; index += ++i) {
46		ENTRY *entry = &hsearch->entries[index & hsearch->index_mask];
47		if (entry->key == NULL)
48			return (entry);
49	}
50}
51
52/*
53 * Computes an FNV-1a hash of the key. Depending on the pointer size, this
54 * either uses the 32- or 64-bit FNV prime.
55 */
56static size_t
57hsearch_hash(size_t offset_basis, const char *str)
58{
59	size_t hash;
60
61	hash = offset_basis;
62	while (*str != '\0') {
63		hash ^= (uint8_t)*str++;
64		if (sizeof(size_t) * CHAR_BIT <= 32)
65			hash *= UINT32_C(16777619);
66		else
67			hash *= UINT64_C(1099511628211);
68	}
69	return (hash);
70}
71
72int
73hsearch_r(ENTRY item, ACTION action, ENTRY **retval, struct hsearch_data *htab)
74{
75	struct __hsearch *hsearch;
76	ENTRY *entry, *old_entries, *new_entries;
77	size_t hash, index, i, old_hash, old_count, new_count;
78
79	hsearch = htab->__hsearch;
80	hash = hsearch_hash(hsearch->offset_basis, item.key);
81
82	/*
83	 * Search the hash table for an existing entry for this key.
84	 * Stop searching if we run into an unused hash table entry.
85	 */
86	for (index = hash, i = 0;; index += ++i) {
87		entry = &hsearch->entries[index & hsearch->index_mask];
88		if (entry->key == NULL)
89			break;
90		if (strcmp(entry->key, item.key) == 0) {
91			*retval = entry;
92			return (1);
93		}
94	}
95
96	/* Only perform the insertion if action is set to ENTER. */
97	if (action == FIND) {
98		errno = ESRCH;
99		return (0);
100	}
101
102	if (hsearch->entries_used * 2 >= hsearch->index_mask) {
103		/* Preserve the old hash table entries. */
104		old_count = hsearch->index_mask + 1;
105		old_entries = hsearch->entries;
106
107		/*
108		 * Allocate and install a new table if insertion would
109		 * yield a hash table that is more than 50% used. By
110		 * using 50% as a threshold, a lookup will only take up
111		 * to two steps on average.
112		 */
113		new_count = (hsearch->index_mask + 1) * 2;
114		new_entries = calloc(new_count, sizeof(ENTRY));
115		if (new_entries == NULL)
116			return (0);
117		hsearch->entries = new_entries;
118		hsearch->index_mask = new_count - 1;
119
120		/* Copy over the entries from the old table to the new table. */
121		for (i = 0; i < old_count; ++i) {
122			entry = &old_entries[i];
123			if (entry->key != NULL) {
124				old_hash = hsearch_hash(hsearch->offset_basis,
125				    entry->key);
126				*hsearch_lookup_free(hsearch, old_hash) =
127				    *entry;
128			}
129		}
130
131		/* Destroy the old hash table entries. */
132		free(old_entries);
133
134		/*
135		 * Perform a new lookup for a free table entry, so that
136		 * we insert the entry into the new hash table.
137		 */
138		hsearch = htab->__hsearch;
139		entry = hsearch_lookup_free(hsearch, hash);
140	}
141
142	/* Insert the new entry into the hash table. */
143	*entry = item;
144	++hsearch->entries_used;
145	*retval = entry;
146	return (1);
147}
148