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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