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