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