1 /***************************************************************************
2 * _ _ ____ _
3 * Project ___| | | | _ \| |
4 * / __| | | | |_) | |
5 * | (__| |_| | _ <| |___
6 * \___|\___/|_| \_\_____|
7 *
8 * Copyright (C) 1997 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
9 *
10 * This software is licensed as described in the file COPYING, which
11 * you should have received as part of this distribution. The terms
12 * are also available at https://curl.haxx.se/docs/copyright.html.
13 *
14 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
15 * copies of the Software, and permit persons to whom the Software is
16 * furnished to do so, under the terms of the COPYING file.
17 *
18 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
19 * KIND, either express or implied.
20 *
21 ***************************************************************************/
22
23 #include "curl_setup.h"
24
25 #include "splay.h"
26
27 /*
28 * This macro compares two node keys i and j and returns:
29 *
30 * negative value: when i is smaller than j
31 * zero : when i is equal to j
32 * positive when : when i is larger than j
33 */
34 #define compare(i,j) Curl_splaycomparekeys((i),(j))
35
36 /*
37 * Splay using the key i (which may or may not be in the tree.) The starting
38 * root is t.
39 */
Curl_splay(struct curltime i,struct Curl_tree * t)40 struct Curl_tree *Curl_splay(struct curltime i,
41 struct Curl_tree *t)
42 {
43 struct Curl_tree N, *l, *r, *y;
44 long comp;
45
46 if(t == NULL)
47 return t;
48 N.smaller = N.larger = NULL;
49 l = r = &N;
50
51 for(;;) {
52 comp = compare(i, t->key);
53 if(comp < 0) {
54 if(t->smaller == NULL)
55 break;
56 if(compare(i, t->smaller->key) < 0) {
57 y = t->smaller; /* rotate smaller */
58 t->smaller = y->larger;
59 y->larger = t;
60 t = y;
61 if(t->smaller == NULL)
62 break;
63 }
64 r->smaller = t; /* link smaller */
65 r = t;
66 t = t->smaller;
67 }
68 else if(comp > 0) {
69 if(t->larger == NULL)
70 break;
71 if(compare(i, t->larger->key) > 0) {
72 y = t->larger; /* rotate larger */
73 t->larger = y->smaller;
74 y->smaller = t;
75 t = y;
76 if(t->larger == NULL)
77 break;
78 }
79 l->larger = t; /* link larger */
80 l = t;
81 t = t->larger;
82 }
83 else
84 break;
85 }
86
87 l->larger = t->smaller; /* assemble */
88 r->smaller = t->larger;
89 t->smaller = N.larger;
90 t->larger = N.smaller;
91
92 return t;
93 }
94
95 /* Insert key i into the tree t. Return a pointer to the resulting tree or
96 * NULL if something went wrong.
97 *
98 * @unittest: 1309
99 */
Curl_splayinsert(struct curltime i,struct Curl_tree * t,struct Curl_tree * node)100 struct Curl_tree *Curl_splayinsert(struct curltime i,
101 struct Curl_tree *t,
102 struct Curl_tree *node)
103 {
104 static const struct curltime KEY_NOTUSED = {
105 (time_t)-1, (unsigned int)-1
106 }; /* will *NEVER* appear */
107
108 if(node == NULL)
109 return t;
110
111 if(t != NULL) {
112 t = Curl_splay(i, t);
113 if(compare(i, t->key) == 0) {
114 /* There already exists a node in the tree with the very same key. Build
115 a doubly-linked circular list of nodes. We add the new 'node' struct
116 to the end of this list. */
117
118 node->key = KEY_NOTUSED; /* we set the key in the sub node to NOTUSED
119 to quickly identify this node as a subnode */
120 node->samen = t;
121 node->samep = t->samep;
122 t->samep->samen = node;
123 t->samep = node;
124
125 return t; /* the root node always stays the same */
126 }
127 }
128
129 if(t == NULL) {
130 node->smaller = node->larger = NULL;
131 }
132 else if(compare(i, t->key) < 0) {
133 node->smaller = t->smaller;
134 node->larger = t;
135 t->smaller = NULL;
136
137 }
138 else {
139 node->larger = t->larger;
140 node->smaller = t;
141 t->larger = NULL;
142 }
143 node->key = i;
144
145 /* no identical nodes (yet), we are the only one in the list of nodes */
146 node->samen = node;
147 node->samep = node;
148 return node;
149 }
150
151 /* Finds and deletes the best-fit node from the tree. Return a pointer to the
152 resulting tree. best-fit means the smallest node if it is not larger than
153 the key */
Curl_splaygetbest(struct curltime i,struct Curl_tree * t,struct Curl_tree ** removed)154 struct Curl_tree *Curl_splaygetbest(struct curltime i,
155 struct Curl_tree *t,
156 struct Curl_tree **removed)
157 {
158 static struct curltime tv_zero = {0, 0};
159 struct Curl_tree *x;
160
161 if(!t) {
162 *removed = NULL; /* none removed since there was no root */
163 return NULL;
164 }
165
166 /* find smallest */
167 t = Curl_splay(tv_zero, t);
168 if(compare(i, t->key) < 0) {
169 /* even the smallest is too big */
170 *removed = NULL;
171 return t;
172 }
173
174 /* FIRST! Check if there is a list with identical keys */
175 x = t->samen;
176 if(x != t) {
177 /* there is, pick one from the list */
178
179 /* 'x' is the new root node */
180
181 x->key = t->key;
182 x->larger = t->larger;
183 x->smaller = t->smaller;
184 x->samep = t->samep;
185 t->samep->samen = x;
186
187 *removed = t;
188 return x; /* new root */
189 }
190
191 /* we splayed the tree to the smallest element, there is no smaller */
192 x = t->larger;
193 *removed = t;
194
195 return x;
196 }
197
198
199 /* Deletes the very node we point out from the tree if it's there. Stores a
200 * pointer to the new resulting tree in 'newroot'.
201 *
202 * Returns zero on success and non-zero on errors! TODO: document error codes.
203 * When returning error, it does not touch the 'newroot' pointer.
204 *
205 * NOTE: when the last node of the tree is removed, there's no tree left so
206 * 'newroot' will be made to point to NULL.
207 *
208 * @unittest: 1309
209 */
Curl_splayremovebyaddr(struct Curl_tree * t,struct Curl_tree * removenode,struct Curl_tree ** newroot)210 int Curl_splayremovebyaddr(struct Curl_tree *t,
211 struct Curl_tree *removenode,
212 struct Curl_tree **newroot)
213 {
214 static const struct curltime KEY_NOTUSED = {
215 (time_t)-1, (unsigned int)-1
216 }; /* will *NEVER* appear */
217 struct Curl_tree *x;
218
219 if(!t || !removenode)
220 return 1;
221
222 if(compare(KEY_NOTUSED, removenode->key) == 0) {
223 /* Key set to NOTUSED means it is a subnode within a 'same' linked list
224 and thus we can unlink it easily. */
225 if(removenode->samen == removenode)
226 /* A non-subnode should never be set to KEY_NOTUSED */
227 return 3;
228
229 removenode->samep->samen = removenode->samen;
230 removenode->samen->samep = removenode->samep;
231
232 /* Ensures that double-remove gets caught. */
233 removenode->samen = removenode;
234
235 *newroot = t; /* return the same root */
236 return 0;
237 }
238
239 t = Curl_splay(removenode->key, t);
240
241 /* First make sure that we got the same root node as the one we want
242 to remove, as otherwise we might be trying to remove a node that
243 isn't actually in the tree.
244
245 We cannot just compare the keys here as a double remove in quick
246 succession of a node with key != KEY_NOTUSED && same != NULL
247 could return the same key but a different node. */
248 if(t != removenode)
249 return 2;
250
251 /* Check if there is a list with identical sizes, as then we're trying to
252 remove the root node of a list of nodes with identical keys. */
253 x = t->samen;
254 if(x != t) {
255 /* 'x' is the new root node, we just make it use the root node's
256 smaller/larger links */
257
258 x->key = t->key;
259 x->larger = t->larger;
260 x->smaller = t->smaller;
261 x->samep = t->samep;
262 t->samep->samen = x;
263 }
264 else {
265 /* Remove the root node */
266 if(t->smaller == NULL)
267 x = t->larger;
268 else {
269 x = Curl_splay(removenode->key, t->smaller);
270 x->larger = t->larger;
271 }
272 }
273
274 *newroot = x; /* store new root pointer */
275
276 return 0;
277 }
278
279