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("$FreeBSD$");
28
29 #define _SEARCH_PRIVATE
30 #include <search.h>
31 #include <stdlib.h>
32
33 #include "tsearch_path.h"
34
35 void *
tsearch(const void * key,void ** rootp,int (* compar)(const void *,const void *))36 tsearch(const void *key, void **rootp,
37 int (*compar)(const void *, const void *))
38 {
39 struct path path;
40 node_t *root, **base, **leaf, *result, *n, *x, *y, *z;
41 int cmp;
42
43 /* POSIX requires that tsearch() returns NULL if rootp is NULL. */
44 if (rootp == NULL)
45 return (NULL);
46 root = *rootp;
47
48 /*
49 * Find the leaf where the new key needs to be inserted. Return
50 * if we've found an existing entry. Keep track of the path that
51 * is taken to get to the node, as we will need it to adjust the
52 * balances.
53 */
54 path_init(&path);
55 base = &root;
56 leaf = &root;
57 while (*leaf != NULL) {
58 if ((*leaf)->balance != 0) {
59 /*
60 * If we reach a node that has a non-zero
61 * balance on the way, we know that we won't
62 * need to perform any rotations above this
63 * point. In this case rotations are always
64 * capable of keeping the subtree in balance.
65 * Make this the base node and reset the path.
66 */
67 base = leaf;
68 path_init(&path);
69 }
70 cmp = compar(key, (*leaf)->key);
71 if (cmp < 0) {
72 path_taking_left(&path);
73 leaf = &(*leaf)->llink;
74 } else if (cmp > 0) {
75 path_taking_right(&path);
76 leaf = &(*leaf)->rlink;
77 } else {
78 return (&(*leaf)->key);
79 }
80 }
81
82 /* Did not find a matching key in the tree. Insert a new node. */
83 result = *leaf = malloc(sizeof(**leaf));
84 if (result == NULL)
85 return (NULL);
86 result->key = (void *)key;
87 result->llink = NULL;
88 result->rlink = NULL;
89 result->balance = 0;
90
91 /*
92 * Walk along the same path a second time and adjust the
93 * balances. Except for the first node, all of these nodes must
94 * have a balance of zero, meaning that these nodes will not get
95 * out of balance.
96 */
97 for (n = *base; n != *leaf;) {
98 if (path_took_left(&path)) {
99 n->balance += 1;
100 n = n->llink;
101 } else {
102 n->balance -= 1;
103 n = n->rlink;
104 }
105 }
106
107 /*
108 * Adjusting the balances may have pushed the balance of the
109 * base node out of range. Perform a rotation to bring the
110 * balance back in range.
111 */
112 x = *base;
113 if (x->balance > 1) {
114 y = x->llink;
115 if (y->balance < 0) {
116 /*
117 * Left-right case.
118 *
119 * x
120 * / \ z
121 * y D / \
122 * / \ --> y x
123 * A z /| |\
124 * / \ A B C D
125 * B C
126 */
127 z = y->rlink;
128 y->rlink = z->llink;
129 z->llink = y;
130 x->llink = z->rlink;
131 z->rlink = x;
132 *base = z;
133
134 x->balance = z->balance > 0 ? -1 : 0;
135 y->balance = z->balance < 0 ? 1 : 0;
136 z->balance = 0;
137 } else {
138 /*
139 * Left-left case.
140 *
141 * x y
142 * / \ / \
143 * y C --> A x
144 * / \ / \
145 * A B B C
146 */
147 x->llink = y->rlink;
148 y->rlink = x;
149 *base = y;
150
151 x->balance = 0;
152 y->balance = 0;
153 }
154 } else if (x->balance < -1) {
155 y = x->rlink;
156 if (y->balance > 0) {
157 /*
158 * Right-left case.
159 *
160 * x
161 * / \ z
162 * A y / \
163 * / \ --> x y
164 * z D /| |\
165 * / \ A B C D
166 * B C
167 */
168 node_t *z = y->llink;
169 x->rlink = z->llink;
170 z->llink = x;
171 y->llink = z->rlink;
172 z->rlink = y;
173 *base = z;
174
175 x->balance = z->balance < 0 ? 1 : 0;
176 y->balance = z->balance > 0 ? -1 : 0;
177 z->balance = 0;
178 } else {
179 /*
180 * Right-right case.
181 *
182 * x y
183 * / \ / \
184 * A y --> x C
185 * / \ / \
186 * B C A B
187 */
188 x->rlink = y->llink;
189 y->llink = x;
190 *base = y;
191
192 x->balance = 0;
193 y->balance = 0;
194 }
195 }
196
197 /* Return the new entry. */
198 *rootp = root;
199 return (&result->key);
200 }
201