1/***************************************************************************
2 * _ _ ____ _
3 * Project ___| | | | _ \| |
4 * / __| | | | |_) | |
5 * | (__| |_| | _ <| |___
6 * \___|\___/|_| \_\_____|
7 *
8 * Copyright (C) 1997 - 2022, Daniel Stenberg, <[email protected]>, 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 */
42struct 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 */
101struct 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 */
155struct 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 */
211int 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