1/***************************************************************************
2 * _ _ ____ _
3 * Project ___| | | | _ \| |
4 * / __| | | | |_) | |
5 * | (__| |_| | _ <| |___
6 * \___|\___/|_| \_\_____|
7 *
8 * Copyright (C) 1997 - 2021, 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 ***************************************************************************/
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 */
40struct Curl_tree *Curl_splay(struct curltime i,
41 struct Curl_tree *t)
42{
43 struct Curl_tree N, *l, *r, *y;
44
45 if(!t)
46 return t;
47 N.smaller = N.larger = NULL;
48 l = r = &N;
49
50 for(;;) {
51 long comp = compare(i, t->key);
52 if(comp < 0) {
53 if(!t->smaller)
54 break;
55 if(compare(i, t->smaller->key) < 0) {
56 y = t->smaller; /* rotate smaller */
57 t->smaller = y->larger;
58 y->larger = t;
59 t = y;
60 if(!t->smaller)
61 break;
62 }
63 r->smaller = t; /* link smaller */
64 r = t;
65 t = t->smaller;
66 }
67 else if(comp > 0) {
68 if(!t->larger)
69 break;
70 if(compare(i, t->larger->key) > 0) {
71 y = t->larger; /* rotate larger */
72 t->larger = y->smaller;
73 y->smaller = t;
74 t = y;
75 if(!t->larger)
76 break;
77 }
78 l->larger = t; /* link larger */
79 l = t;
80 t = t->larger;
81 }
82 else
83 break;
84 }
85
86 l->larger = t->smaller; /* assemble */
87 r->smaller = t->larger;
88 t->smaller = N.larger;
89 t->larger = N.smaller;
90
91 return t;
92}
93
94/* Insert key i into the tree t. Return a pointer to the resulting tree or
95 * NULL if something went wrong.
96 *
97 * @unittest: 1309
98 */
99struct Curl_tree *Curl_splayinsert(struct curltime i,
100 struct Curl_tree *t,
101 struct Curl_tree *node)
102{
103 static const struct curltime KEY_NOTUSED = {
104 (time_t)-1, (unsigned int)-1
105 }; /* will *NEVER* appear */
106
107 if(!node)
108 return t;
109
110 if(t != NULL) {
111 t = Curl_splay(i, t);
112 if(compare(i, t->key) == 0) {
113 /* There already exists a node in the tree with the very same key. Build
114 a doubly-linked circular list of nodes. We add the new 'node' struct
115 to the end of this list. */
116
117 node->key = KEY_NOTUSED; /* we set the key in the sub node to NOTUSED
118 to quickly identify this node as a subnode */
119 node->samen = t;
120 node->samep = t->samep;
121 t->samep->samen = node;
122 t->samep = node;
123
124 return t; /* the root node always stays the same */
125 }
126 }
127
128 if(!t) {
129 node->smaller = node->larger = NULL;
130 }
131 else if(compare(i, t->key) < 0) {
132 node->smaller = t->smaller;
133 node->larger = t;
134 t->smaller = NULL;
135
136 }
137 else {
138 node->larger = t->larger;
139 node->smaller = t;
140 t->larger = NULL;
141 }
142 node->key = i;
143
144 /* no identical nodes (yet), we are the only one in the list of nodes */
145 node->samen = node;
146 node->samep = node;
147 return node;
148}
149
150/* Finds and deletes the best-fit node from the tree. Return a pointer to the
151 resulting tree. best-fit means the smallest node if it is not larger than
152 the key */
153struct Curl_tree *Curl_splaygetbest(struct curltime i,
154 struct Curl_tree *t,
155 struct Curl_tree **removed)
156{
157 static struct curltime tv_zero = {0, 0};
158 struct Curl_tree *x;
159
160 if(!t) {
161 *removed = NULL; /* none removed since there was no root */
162 return NULL;
163 }
164
165 /* find smallest */
166 t = Curl_splay(tv_zero, t);
167 if(compare(i, t->key) < 0) {
168 /* even the smallest is too big */
169 *removed = NULL;
170 return t;
171 }
172
173 /* FIRST! Check if there is a list with identical keys */
174 x = t->samen;
175 if(x != t) {
176 /* there is, pick one from the list */
177
178 /* 'x' is the new root node */
179
180 x->key = t->key;
181 x->larger = t->larger;
182 x->smaller = t->smaller;
183 x->samep = t->samep;
184 t->samep->samen = x;
185
186 *removed = t;
187 return x; /* new root */
188 }
189
190 /* we splayed the tree to the smallest element, there is no smaller */
191 x = t->larger;
192 *removed = t;
193
194 return x;
195}
196
197
198/* Deletes the very node we point out from the tree if it's there. Stores a
199 * pointer to the new resulting tree in 'newroot'.
200 *
201 * Returns zero on success and non-zero on errors!
202 * When returning error, it does not touch the 'newroot' pointer.
203 *
204 * NOTE: when the last node of the tree is removed, there's no tree left so
205 * 'newroot' will be made to point to NULL.
206 *
207 * @unittest: 1309
208 */
209int Curl_splayremove(struct Curl_tree *t,
210 struct Curl_tree *removenode,
211 struct Curl_tree **newroot)
212{
213 static const struct curltime KEY_NOTUSED = {
214 (time_t)-1, (unsigned int)-1
215 }; /* will *NEVER* appear */
216 struct Curl_tree *x;
217
218 if(!t || !removenode)
219 return 1;
220
221 if(compare(KEY_NOTUSED, removenode->key) == 0) {
222 /* Key set to NOTUSED means it is a subnode within a 'same' linked list
223 and thus we can unlink it easily. */
224 if(removenode->samen == removenode)
225 /* A non-subnode should never be set to KEY_NOTUSED */
226 return 3;
227
228 removenode->samep->samen = removenode->samen;
229 removenode->samen->samep = removenode->samep;
230
231 /* Ensures that double-remove gets caught. */
232 removenode->samen = removenode;
233
234 *newroot = t; /* return the same root */
235 return 0;
236 }
237
238 t = Curl_splay(removenode->key, t);
239
240 /* First make sure that we got the same root node as the one we want
241 to remove, as otherwise we might be trying to remove a node that
242 isn't actually in the tree.
243
244 We cannot just compare the keys here as a double remove in quick
245 succession of a node with key != KEY_NOTUSED && same != NULL
246 could return the same key but a different node. */
247 if(t != removenode)
248 return 2;
249
250 /* Check if there is a list with identical sizes, as then we're trying to
251 remove the root node of a list of nodes with identical keys. */
252 x = t->samen;
253 if(x != t) {
254 /* 'x' is the new root node, we just make it use the root node's
255 smaller/larger links */
256
257 x->key = t->key;
258 x->larger = t->larger;
259 x->smaller = t->smaller;
260 x->samep = t->samep;
261 t->samep->samen = x;
262 }
263 else {
264 /* Remove the root node */
265 if(!t->smaller)
266 x = t->larger;
267 else {
268 x = Curl_splay(removenode->key, t->smaller);
269 x->larger = t->larger;
270 }
271 }
272
273 *newroot = x; /* store new root pointer */
274
275 return 0;
276}
277