/src/curl/lib/splay.c

Source
/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * SPDX-License-Identifier: curl
 *
 ***************************************************************************/

#include "curl_setup.h"

#include "curlx/timeval.h"
#include "splay.h"

/*
 * This macro compares two node keys i and j and returns:
 *
 *  negative value: when i is smaller than j
 *  zero          : when i is equal   to   j
 *  positive when : when i is larger  than j
 */
#define compare(i, j) curlx_timediff_us(i, j)

/*
 * Splay using the key i (which may or may not be in the tree.) The starting
 * root is t.
 */
struct Curl_tree *Curl_splay(struct curltime i,
                             struct Curl_tree *t)
{
  struct Curl_tree N, *l, *r, *y;

  if(!t)
    return NULL;
  N.smaller = N.larger = NULL;
  l = r = &N;

  for(;;) {
    timediff_t comp = compare(i, t->key);
    if(comp < 0) {
      if(!t->smaller)
        break;
      if(compare(i, t->smaller->key) < 0) {
        y = t->smaller;                           /* rotate smaller */
        t->smaller = y->larger;
        y->larger = t;
        t = y;
        if(!t->smaller)
          break;
      }
      r->smaller = t;                               /* link smaller */
      r = t;
      t = t->smaller;
    }
    else if(comp > 0) {
      if(!t->larger)
        break;
      if(compare(i, t->larger->key) > 0) {
        y = t->larger;                          /* rotate larger */
        t->larger = y->smaller;
        y->smaller = t;
        t = y;
        if(!t->larger)
          break;
      }
      l->larger = t;                              /* link larger */
      l = t;
      t = t->larger;
    }
    else
      break;
  }

  l->larger = t->smaller;                                /* assemble */
  r->smaller = t->larger;
  t->smaller = N.larger;
  t->larger = N.smaller;

  return t;
}

static const struct curltime SPLAY_SUBNODE = {
  ~0, -1
};

/* Insert key i into the tree t. Return a pointer to the resulting tree or
 * NULL if something went wrong.
 *
 * @unittest: 1309
 */
struct Curl_tree *Curl_splayinsert(struct curltime i,
                                   struct Curl_tree *t,
                                   struct Curl_tree *node)
{
  DEBUGASSERT(node);

  if(t) {
    t = Curl_splay(i, t);
    DEBUGASSERT(t);
    if(compare(i, t->key) == 0) {
      /* There already exists a node in the tree with the same key. Build a
         doubly-linked circular list of nodes. We add the new 'node' struct to
         the end of this list. */

      node->key = SPLAY_SUBNODE; /* identify this node as a subnode */
      node->samen = t;
      node->samep = t->samep;
      t->samep->samen = node;
      t->samep = node;

      return t; /* the root node always stays the same */
    }
  }

  if(!t) {
    node->smaller = node->larger = NULL;
  }
  else if(compare(i, t->key) < 0) {
    node->smaller = t->smaller;
    node->larger = t;
    t->smaller = NULL;
  }
  else {
    node->larger = t->larger;
    node->smaller = t;
    t->larger = NULL;
  }
  node->key = i;

  /* no identical nodes (yet), we are the only one in the list of nodes */
  node->samen = node;
  node->samep = node;
  return node;
}

/* Finds and deletes the best-fit node from the tree. Return a pointer to the
   resulting tree. best-fit means the smallest node if it is not larger than
   the key */
struct Curl_tree *Curl_splaygetbest(struct curltime i,
                                    struct Curl_tree *t,
                                    struct Curl_tree **removed)
{
  static const struct curltime tv_zero = { 0, 0 };
  struct Curl_tree *x;

  if(!t) {
    *removed = NULL; /* none removed since there was no root */
    return NULL;
  }

  /* find smallest */
  t = Curl_splay(tv_zero, t);
  DEBUGASSERT(t);
  if(compare(i, t->key) < 0) {
    /* even the smallest is too big */
    *removed = NULL;
    return t;
  }

  /* FIRST! Check if there is a list with identical keys */
  x = t->samen;
  if(x != t) {
    /* there is, pick one from the list */

    /* 'x' is the new root node */

    x->key = t->key;
    x->larger = t->larger;
    x->smaller = t->smaller;
    x->samep = t->samep;
    t->samep->samen = x;

    *removed = t;
    return x; /* new root */
  }

  /* we splayed the tree to the smallest element, there is no smaller */
  x = t->larger;
  *removed = t;

  return x;
}

/* Deletes the node we point out from the tree if it is there. Stores a
 * pointer to the new resulting tree in 'newroot'.
 *
 * Returns zero on success and non-zero on errors!
 * When returning error, it does not touch the 'newroot' pointer.
 *
 * NOTE: when the last node of the tree is removed, there is no tree left so
 * 'newroot' will be made to point to NULL.
 *
 * @unittest: 1309
 */
int Curl_splayremove(struct Curl_tree *t,
                     struct Curl_tree *removenode,
                     struct Curl_tree **newroot)
{
  struct Curl_tree *x;

  if(!t)
    return 1;

  DEBUGASSERT(removenode);

  if(compare(SPLAY_SUBNODE, removenode->key) == 0) {
    /* It is a subnode within a 'same' linked list and thus we can unlink it
       easily. */
    DEBUGASSERT(removenode->samen != removenode);
    if(removenode->samen == removenode)
      /* A non-subnode should never be set to SPLAY_SUBNODE */
      return 3;

    removenode->samep->samen = removenode->samen;
    removenode->samen->samep = removenode->samep;

    /* Ensures that double-remove gets caught. */
    removenode->samen = removenode;

    *newroot = t; /* return the same root */
    return 0;
  }

  t = Curl_splay(removenode->key, t);
  DEBUGASSERT(t);

  /* First make sure that we got the same root node as the one we want
     to remove, as otherwise we might be trying to remove a node that
     is not actually in the tree.

     We cannot just compare the keys here as a double remove in quick
     succession of a node with key != SPLAY_SUBNODE && same != NULL
     could return the same key but a different node. */
  DEBUGASSERT(t == removenode);
  if(t != removenode)
    return 2;

  /* Check if there is a list with identical sizes, as then we are trying to
     remove the root node of a list of nodes with identical keys. */
  x = t->samen;
  if(x != t) {
    /* 'x' is the new root node, we just make it use the root node's
       smaller/larger links */

    x->key = t->key;
    x->larger = t->larger;
    x->smaller = t->smaller;
    x->samep = t->samep;
    t->samep->samen = x;
  }
  else {
    /* Remove the root node */
    if(!t->smaller)
      x = t->larger;
    else {
      x = Curl_splay(removenode->key, t->smaller);
      DEBUGASSERT(x);
      x->larger = t->larger;
    }
  }

  *newroot = x; /* store new root pointer */

  return 0;
}

/* set and get the custom payload for this tree node */
void Curl_splayset(struct Curl_tree *node, void *payload)
{
  DEBUGASSERT(node);
  node->ptr = payload;
}

void *Curl_splayget(struct Curl_tree *node)
{
  DEBUGASSERT(node);
  return node->ptr;
}

Coverage Report

Created: 2025-12-04 06:52

Line	Count	Source
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 "curlx/timeval.h"
28		#include "splay.h"
29
30		/*
31		* This macro compares two node keys i and j and returns:
32		*
33		* negative value: when i is smaller than j
34		* zero : when i is equal to j
35		* positive when : when i is larger than j
36		*/
37	0	#define compare(i, j) curlx_timediff_us(i, j)
38
39		/*
40		* Splay using the key i (which may or may not be in the tree.) The starting
41		* root is t.
42		*/
43		struct Curl_tree *Curl_splay(struct curltime i,
44		struct Curl_tree *t)
45	0	{
46	0	struct Curl_tree N, l, r, *y;
47
48	0	if(!t)
49	0	return NULL;
50	0	N.smaller = N.larger = NULL;
51	0	l = r = &N;
52
53	0	for(;;) {
54	0	timediff_t comp = compare(i, t->key);
55	0	if(comp < 0) {
56	0	if(!t->smaller)
57	0	break;
58	0	if(compare(i, t->smaller->key) < 0) {
59	0	y = t->smaller; /* rotate smaller */
60	0	t->smaller = y->larger;
61	0	y->larger = t;
62	0	t = y;
63	0	if(!t->smaller)
64	0	break;
65	0	}
66	0	r->smaller = t; /* link smaller */
67	0	r = t;
68	0	t = t->smaller;
69	0	}
70	0	else if(comp > 0) {
71	0	if(!t->larger)
72	0	break;
73	0	if(compare(i, t->larger->key) > 0) {
74	0	y = t->larger; /* rotate larger */
75	0	t->larger = y->smaller;
76	0	y->smaller = t;
77	0	t = y;
78	0	if(!t->larger)
79	0	break;
80	0	}
81	0	l->larger = t; /* link larger */
82	0	l = t;
83	0	t = t->larger;
84	0	}
85	0	else
86	0	break;
87	0	}
88
89	0	l->larger = t->smaller; /* assemble */
90	0	r->smaller = t->larger;
91	0	t->smaller = N.larger;
92	0	t->larger = N.smaller;
93
94	0	return t;
95	0	}
96
97		static const struct curltime SPLAY_SUBNODE = {
98		~0, -1
99		};
100
101		/* Insert key i into the tree t. Return a pointer to the resulting tree or
102		* NULL if something went wrong.
103		*
104		* @unittest: 1309
105		*/
106		struct Curl_tree *Curl_splayinsert(struct curltime i,
107		struct Curl_tree *t,
108		struct Curl_tree *node)
109	0	{
110	0	DEBUGASSERT(node);
111
112	0	if(t) {
113	0	t = Curl_splay(i, t);
114	0	DEBUGASSERT(t);
115	0	if(compare(i, t->key) == 0) {
116		/* There already exists a node in the tree with the same key. Build a
117		doubly-linked circular list of nodes. We add the new 'node' struct to
118		the end of this list. */
119
120	0	node->key = SPLAY_SUBNODE; /* identify this node as a subnode */
121	0	node->samen = t;
122	0	node->samep = t->samep;
123	0	t->samep->samen = node;
124	0	t->samep = node;
125
126	0	return t; /* the root node always stays the same */
127	0	}
128	0	}
129
130	0	if(!t) {
131	0	node->smaller = node->larger = NULL;
132	0	}
133	0	else if(compare(i, t->key) < 0) {
134	0	node->smaller = t->smaller;
135	0	node->larger = t;
136	0	t->smaller = NULL;
137	0	}
138	0	else {
139	0	node->larger = t->larger;
140	0	node->smaller = t;
141	0	t->larger = NULL;
142	0	}
143	0	node->key = i;
144
145		/* no identical nodes (yet), we are the only one in the list of nodes */
146	0	node->samen = node;
147	0	node->samep = node;
148	0	return node;
149	0	}
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 */
154		struct Curl_tree *Curl_splaygetbest(struct curltime i,
155		struct Curl_tree *t,
156		struct Curl_tree **removed)
157	0	{
158	0	static const struct curltime tv_zero = { 0, 0 };
159	0	struct Curl_tree *x;
160
161	0	if(!t) {
162	0	removed = NULL; / none removed since there was no root */
163	0	return NULL;
164	0	}
165
166		/* find smallest */
167	0	t = Curl_splay(tv_zero, t);
168	0	DEBUGASSERT(t);
169	0	if(compare(i, t->key) < 0) {
170		/* even the smallest is too big */
171	0	*removed = NULL;
172	0	return t;
173	0	}
174
175		/* FIRST! Check if there is a list with identical keys */
176	0	x = t->samen;
177	0	if(x != t) {
178		/* there is, pick one from the list */
179
180		/* 'x' is the new root node */
181
182	0	x->key = t->key;
183	0	x->larger = t->larger;
184	0	x->smaller = t->smaller;
185	0	x->samep = t->samep;
186	0	t->samep->samen = x;
187
188	0	*removed = t;
189	0	return x; /* new root */
190	0	}
191
192		/* we splayed the tree to the smallest element, there is no smaller */
193	0	x = t->larger;
194	0	*removed = t;
195
196	0	return x;
197	0	}
198
199		/* Deletes the node we point out from the tree if it is there. Stores a
200		* pointer to the new resulting tree in 'newroot'.
201		*
202		* Returns zero on success and non-zero on errors!
203		* When returning error, it does not touch the 'newroot' pointer.
204		*
205		* NOTE: when the last node of the tree is removed, there is no tree left so
206		* 'newroot' will be made to point to NULL.
207		*
208		* @unittest: 1309
209		*/
210		int Curl_splayremove(struct Curl_tree *t,
211		struct Curl_tree *removenode,
212		struct Curl_tree **newroot)
213	0	{
214	0	struct Curl_tree *x;
215
216	0	if(!t)
217	0	return 1;
218
219	0	DEBUGASSERT(removenode);
220
221	0	if(compare(SPLAY_SUBNODE, removenode->key) == 0) {
222		/* It is a subnode within a 'same' linked list and thus we can unlink it
223		easily. */
224	0	DEBUGASSERT(removenode->samen != removenode);
225	0	if(removenode->samen == removenode)
226		/* A non-subnode should never be set to SPLAY_SUBNODE */
227	0	return 3;
228
229	0	removenode->samep->samen = removenode->samen;
230	0	removenode->samen->samep = removenode->samep;
231
232		/* Ensures that double-remove gets caught. */
233	0	removenode->samen = removenode;
234
235	0	newroot = t; / return the same root */
236	0	return 0;
237	0	}
238
239	0	t = Curl_splay(removenode->key, t);
240	0	DEBUGASSERT(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		is not 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 != SPLAY_SUBNODE && same != NULL
248		could return the same key but a different node. */
249	0	DEBUGASSERT(t == removenode);
250	0	if(t != removenode)
251	0	return 2;
252
253		/* Check if there is a list with identical sizes, as then we are trying to
254		remove the root node of a list of nodes with identical keys. */
255	0	x = t->samen;
256	0	if(x != t) {
257		/* 'x' is the new root node, we just make it use the root node's
258		smaller/larger links */
259
260	0	x->key = t->key;
261	0	x->larger = t->larger;
262	0	x->smaller = t->smaller;
263	0	x->samep = t->samep;
264	0	t->samep->samen = x;
265	0	}
266	0	else {
267		/* Remove the root node */
268	0	if(!t->smaller)
269	0	x = t->larger;
270	0	else {
271	0	x = Curl_splay(removenode->key, t->smaller);
272	0	DEBUGASSERT(x);
273	0	x->larger = t->larger;
274	0	}
275	0	}
276
277	0	newroot = x; / store new root pointer */
278
279	0	return 0;
280	0	}
281
282		/* set and get the custom payload for this tree node */
283		void Curl_splayset(struct Curl_tree node, void payload)
284	0	{
285	0	DEBUGASSERT(node);
286	0	node->ptr = payload;
287	0	}
288
289		void Curl_splayget(struct Curl_tree node)
290	0	{
291	0	DEBUGASSERT(node);
292	0	return node->ptr;
293	0	}