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1 /***************************************************************************
2  *                                  _   _ ____  _
3  *  Project                     ___| | | |  _ \| |
4  *                             / __| | | | |_) | |
5  *                            | (__| |_| |  _ <| |___
6  *                             \___|\___/|_| \_\_____|
7  *
8  * Copyright (C) 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.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  * SPDX-License-Identifier: curl
22  *
23  ***************************************************************************/
24 
25 #include "curl_setup.h"
26 
27 #include "splay.h"
28 
29 /*
30  * This macro compares two node keys i and j and returns:
31  *
32  *  negative value: when i is smaller than j
33  *  zero          : when i is equal   to   j
34  *  positive when : when i is larger  than j
35  */
36 #define compare(i,j) Curl_splaycomparekeys((i),(j))
37 
38 /*
39  * Splay using the key i (which may or may not be in the tree.) The starting
40  * root is t.
41  */
Curl_splay(struct curltime i,struct Curl_tree * t)42 struct Curl_tree *Curl_splay(struct curltime i,
43                              struct Curl_tree *t)
44 {
45   struct Curl_tree N, *l, *r, *y;
46 
47   if(!t)
48     return t;
49   N.smaller = N.larger = NULL;
50   l = r = &N;
51 
52   for(;;) {
53     long comp = compare(i, t->key);
54     if(comp < 0) {
55       if(!t->smaller)
56         break;
57       if(compare(i, t->smaller->key) < 0) {
58         y = t->smaller;                           /* rotate smaller */
59         t->smaller = y->larger;
60         y->larger = t;
61         t = y;
62         if(!t->smaller)
63           break;
64       }
65       r->smaller = t;                               /* link smaller */
66       r = t;
67       t = t->smaller;
68     }
69     else if(comp > 0) {
70       if(!t->larger)
71         break;
72       if(compare(i, t->larger->key) > 0) {
73         y = t->larger;                          /* rotate larger */
74         t->larger = y->smaller;
75         y->smaller = t;
76         t = y;
77         if(!t->larger)
78           break;
79       }
80       l->larger = t;                              /* link larger */
81       l = t;
82       t = t->larger;
83     }
84     else
85       break;
86   }
87 
88   l->larger = t->smaller;                                /* assemble */
89   r->smaller = t->larger;
90   t->smaller = N.larger;
91   t->larger = N.smaller;
92 
93   return t;
94 }
95 
96 /* Insert key i into the tree t.  Return a pointer to the resulting tree or
97  * NULL if something went wrong.
98  *
99  * @unittest: 1309
100  */
Curl_splayinsert(struct curltime i,struct Curl_tree * t,struct Curl_tree * node)101 struct Curl_tree *Curl_splayinsert(struct curltime i,
102                                    struct Curl_tree *t,
103                                    struct Curl_tree *node)
104 {
105   static const struct curltime KEY_NOTUSED = {
106     ~0, -1
107   }; /* will *NEVER* appear */
108 
109   if(!node)
110     return t;
111 
112   if(t) {
113     t = Curl_splay(i, t);
114     if(compare(i, t->key) == 0) {
115       /* There already exists a node in the tree with the very same key. Build
116          a doubly-linked circular list of nodes. We add the new 'node' struct
117          to the end of this list. */
118 
119       node->key = KEY_NOTUSED; /* we set the key in the sub node to NOTUSED
120                                   to quickly identify this node as a subnode */
121       node->samen = t;
122       node->samep = t->samep;
123       t->samep->samen = node;
124       t->samep = node;
125 
126       return t; /* the root node always stays the same */
127     }
128   }
129 
130   if(!t) {
131     node->smaller = node->larger = NULL;
132   }
133   else if(compare(i, t->key) < 0) {
134     node->smaller = t->smaller;
135     node->larger = t;
136     t->smaller = NULL;
137 
138   }
139   else {
140     node->larger = t->larger;
141     node->smaller = t;
142     t->larger = NULL;
143   }
144   node->key = i;
145 
146   /* no identical nodes (yet), we are the only one in the list of nodes */
147   node->samen = node;
148   node->samep = node;
149   return node;
150 }
151 
152 /* Finds and deletes the best-fit node from the tree. Return a pointer to the
153    resulting tree.  best-fit means the smallest node if it is not larger than
154    the key */
Curl_splaygetbest(struct curltime i,struct Curl_tree * t,struct Curl_tree ** removed)155 struct Curl_tree *Curl_splaygetbest(struct curltime i,
156                                     struct Curl_tree *t,
157                                     struct Curl_tree **removed)
158 {
159   static const struct curltime tv_zero = {0, 0};
160   struct Curl_tree *x;
161 
162   if(!t) {
163     *removed = NULL; /* none removed since there was no root */
164     return NULL;
165   }
166 
167   /* find smallest */
168   t = Curl_splay(tv_zero, t);
169   if(compare(i, t->key) < 0) {
170     /* even the smallest is too big */
171     *removed = NULL;
172     return t;
173   }
174 
175   /* FIRST! Check if there is a list with identical keys */
176   x = t->samen;
177   if(x != t) {
178     /* there is, pick one from the list */
179 
180     /* 'x' is the new root node */
181 
182     x->key = t->key;
183     x->larger = t->larger;
184     x->smaller = t->smaller;
185     x->samep = t->samep;
186     t->samep->samen = x;
187 
188     *removed = t;
189     return x; /* new root */
190   }
191 
192   /* we splayed the tree to the smallest element, there is no smaller */
193   x = t->larger;
194   *removed = t;
195 
196   return x;
197 }
198 
199 
200 /* Deletes the very node we point out from the tree if it's there. Stores a
201  * pointer to the new resulting tree in 'newroot'.
202  *
203  * Returns zero on success and non-zero on errors!
204  * When returning error, it does not touch the 'newroot' pointer.
205  *
206  * NOTE: when the last node of the tree is removed, there's no tree left so
207  * 'newroot' will be made to point to NULL.
208  *
209  * @unittest: 1309
210  */
Curl_splayremove(struct Curl_tree * t,struct Curl_tree * removenode,struct Curl_tree ** newroot)211 int Curl_splayremove(struct Curl_tree *t,
212                      struct Curl_tree *removenode,
213                      struct Curl_tree **newroot)
214 {
215   static const struct curltime KEY_NOTUSED = {
216     ~0, -1
217   }; /* will *NEVER* appear */
218   struct Curl_tree *x;
219 
220   if(!t || !removenode)
221     return 1;
222 
223   if(compare(KEY_NOTUSED, removenode->key) == 0) {
224     /* Key set to NOTUSED means it is a subnode within a 'same' linked list
225        and thus we can unlink it easily. */
226     if(removenode->samen == removenode)
227       /* A non-subnode should never be set to KEY_NOTUSED */
228       return 3;
229 
230     removenode->samep->samen = removenode->samen;
231     removenode->samen->samep = removenode->samep;
232 
233     /* Ensures that double-remove gets caught. */
234     removenode->samen = removenode;
235 
236     *newroot = t; /* return the same root */
237     return 0;
238   }
239 
240   t = Curl_splay(removenode->key, t);
241 
242   /* First make sure that we got the same root node as the one we want
243      to remove, as otherwise we might be trying to remove a node that
244      isn't actually in the tree.
245 
246      We cannot just compare the keys here as a double remove in quick
247      succession of a node with key != KEY_NOTUSED && same != NULL
248      could return the same key but a different node. */
249   if(t != removenode)
250     return 2;
251 
252   /* Check if there is a list with identical sizes, as then we're trying to
253      remove the root node of a list of nodes with identical keys. */
254   x = t->samen;
255   if(x != t) {
256     /* 'x' is the new root node, we just make it use the root node's
257        smaller/larger links */
258 
259     x->key = t->key;
260     x->larger = t->larger;
261     x->smaller = t->smaller;
262     x->samep = t->samep;
263     t->samep->samen = x;
264   }
265   else {
266     /* Remove the root node */
267     if(!t->smaller)
268       x = t->larger;
269     else {
270       x = Curl_splay(removenode->key, t->smaller);
271       x->larger = t->larger;
272     }
273   }
274 
275   *newroot = x; /* store new root pointer */
276 
277   return 0;
278 }
279