Sat, 17 Feb 2024 20:22:13 +0100
improve tree iterator struct and add signature for a function that can create an iterator
relates to #371
1 /*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
3 *
4 * Copyright 2024 Mike Becker, Olaf Wintermann All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 *
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
20 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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27 */
28 /**
29 * \file tree.h
30 * \brief Interface for tree implementations.
31 * \author Mike Becker
32 * \author Olaf Wintermann
33 * \copyright 2-Clause BSD License
34 */
36 #ifndef UCX_TREE_H
37 #define UCX_TREE_H
39 #include "common.h"
41 #include "iterator.h"
43 #ifdef __cplusplus
44 extern "C" {
45 #endif
47 /**
48 * When entering a node.
49 */
50 #define CX_TREE_ITERATOR_ENTER 0x1
51 /**
52 * When advancing to the next child.
53 */
54 #define CX_TREE_ITERATOR_NEXT_CHILD 0x2
55 /**
56 * When exiting the node.
57 */
58 #define CX_TREE_ITERATOR_EXIT 0x4
60 /**
61 * Tree iterator.
62 *
63 * This iterator is not position-aware in a strict sense, as it does not assume a particular order of elements in the
64 * tree. However, the iterator keeps track of the number of nodes it has passed in a counter variable.
65 * Each node, regardless of the number of passes, is counted only once.
66 *
67 * @note Objects that are pointed to by an iterator are mutable through that iterator. However, if the
68 * iterator is based on a collection and the underlying collection is mutated by other means than this iterator
69 * (e.g. elements added or removed), the iterator becomes invalid (regardless of what cxIteratorValid() returns)
70 * and MUST be re-obtained from the collection.
71 *
72 * @see CxIterator
73 */
74 typedef struct cx_tree_iterator_s {
75 /**
76 * The base properties of this iterator.
77 */
78 struct cx_iterator_base_s base;
79 /**
80 * The passes that are requested by this iterator.
81 * A combination of the flags #CX_TREE_ITERATOR_ENTER, #CX_TREE_ITERATOR_NEXT_CHILD, #CX_TREE_ITERATOR_EXIT.
82 *
83 * Changing the value after beginning the iteration is unspecified.
84 */
85 uint8_t requested_passes;
86 /**
87 * The current pass.
88 *
89 * @see CX_TREE_ITERATOR_ENTER
90 * @see CX_TREE_ITERATOR_NEXT_CHILD
91 * @see CX_TREE_ITERATOR_EXIT
92 */
93 uint8_t current_pass;
94 /**
95 * Offset in the node struct for the children linked list.
96 */
97 off_t loc_children;
98 /**
99 * Offset in the node struct for the next pointer.
100 */
101 off_t loc_next;
102 /**
103 * The total number of distinct nodes that have been passed so far.
104 */
105 size_t counter;
106 /**
107 * The currently observed node.
108 *
109 * This is the same what cxIteratorCurrent() would return.
110 */
111 void *node;
112 /**
113 * The node where we came from.
114 *
115 * - When entering the root node, this is \c NULL.
116 * - When entering another node, this is the node's parent.
117 * - When advancing to the next child, this is the previous child.
118 */
119 void *source;
120 /**
121 * Internal stack.
122 * Will be automatically freed once the iterator becomes invalid.
123 *
124 * If you want to discard the iterator before, you need to manually
125 * call cxTreeIteratorDispose().
126 */
127 void **stack;
128 /**
129 * Internal capacity of the stack.
130 */
131 size_t stack_capacity;
132 /**
133 * Current depth.
134 */
135 size_t depth;
136 } CxTreeIterator;
138 /**
139 * Releases internal memory of the given tree iterator.
140 * @param iter the iterator
141 */
142 static inline void cxTreeIteratorDispose(CxTreeIterator *iter) {
143 free(iter->stack);
144 }
146 /**
147 * Links a node to a (new) parent.
148 *
149 * If the node has already a parent, it is unlinked, first.
150 * If the parent has children already, the node is prepended to the list
151 * of all currently existing children.
152 *
153 * @param parent the parent node
154 * @param node the node that shall be linked
155 * @param loc_parent offset in the node struct for the parent pointer
156 * @param loc_children offset in the node struct for the children linked list
157 * @param loc_prev offset in the node struct for the prev pointer
158 * @param loc_next offset in the node struct for the next pointer
159 * @see cx_tree_unlink()
160 */
161 __attribute__((__nonnull__))
162 void cx_tree_link(
163 void * restrict parent,
164 void * restrict node,
165 ptrdiff_t loc_parent,
166 ptrdiff_t loc_children,
167 ptrdiff_t loc_prev,
168 ptrdiff_t loc_next
169 );
171 /**
172 * Unlinks a node from its parent.
173 *
174 * If the node has no parent, this function does nothing.
175 *
176 * @param node the node that shall be unlinked from its parent
177 * @param loc_parent offset in the node struct for the parent pointer
178 * @param loc_children offset in the node struct for the children linked list
179 * @param loc_prev offset in the node struct for the prev pointer
180 * @param loc_next offset in the node struct for the next pointer
181 * @see cx_tree_link()
182 */
183 __attribute__((__nonnull__))
184 void cx_tree_unlink(
185 void *node,
186 ptrdiff_t loc_parent,
187 ptrdiff_t loc_children,
188 ptrdiff_t loc_prev,
189 ptrdiff_t loc_next
190 );
192 /**
193 * Function pointer for a search function.
194 *
195 * A function of this kind shall check if the specified \p node
196 * contains the given \p data or if one of the children might contain
197 * the data.
198 *
199 * The function should use the returned integer to indicate how close the
200 * match is, where a negative number means that it does not match at all.
201 *
202 * For example if a tree stores file path information, a node that is
203 * describing a parent directory of a filename that is searched, shall
204 * return a positive number to indicate that a child node might contain the
205 * searched item. On the other hand, if the node denotes a path that is not a
206 * prefix of the searched filename, the function would return -1 to indicate
207 * that * the search does not need to be continued in that branch.
208 *
209 * @param node the node that is currently investigated
210 * @param data the data that is searched for
211 *
212 * @return 0 if the node contains the data,
213 * positive if one of the children might contain the data,
214 * negative if neither the node, nor the children contains the data
215 */
216 typedef int (*cx_tree_search_func)(void const *node, void const* data);
219 /**
220 * Searches for data in a tree.
221 *
222 * When the data cannot be found exactly, the search function might return a
223 * closest result which might be a good starting point for adding a new node
224 * to the tree.
225 *
226 * Depending on the tree structure it is not necessarily guaranteed that the
227 * "closest" match is uniquely defined. This function will search for a node
228 * with the best match according to the \p sfunc (meaning: the return value of
229 * \p sfunc which is closest to zero). If that is also ambiguous, an arbitrary
230 * node matching the criteria is returned.
231 *
232 * @param root the root node
233 * @param data the data to search for
234 * @param sfunc the search function
235 * @param result where the result shall be stored
236 * @param loc_children offset in the node struct for the children linked list
237 * @param loc_next offset in the node struct for the next pointer
238 * @return zero if the node was found exactly, positive if a node was found that
239 * could contain the node (but doesn't right now), negative if the tree does not
240 * contain any node that might be related to the searched data
241 */
242 __attribute__((__nonnull__))
243 int cx_tree_search(
244 void const *root,
245 void const *data,
246 cx_tree_search_func sfunc,
247 void **result,
248 ptrdiff_t loc_children,
249 ptrdiff_t loc_next
250 );
252 /**
253 * Creates an iterator for a tree with the specified root node.
254 *
255 * The \p passes argument is supposed to be a combination of the flags
256 * #CX_TREE_ITERATOR_ENTER, #CX_TREE_ITERATOR_NEXT_CHILD, and #CX_TREE_ITERATOR_EXIT.
257 * Alternatively, the integer 1 is equivalent to just specifying #CX_TREE_ITERATOR_ENTER
258 * which will cause the iterator to pass every node only once (when entering the node).
259 *
260 * When #CX_TREE_ITERATOR_EXIT is set, the iterator will visit a parent node again,
261 * when \em every of it's children has been visited (including the case when the node does not have any children).
262 *
263 * When #CX_TREE_ITERATOR_NEXT_CHILD is set, the iterator will visit a parent node again,
264 * when advancing from one child to the next.
265 *
266 * @note A tree iterator needs to maintain a stack of visited nodes, which is allocated using stdlib malloc().
267 * When the iterator becomes invalid, this memory is automatically released. However, if you wish to cancel the
268 * iteration before the iterator becomes invalid by itself, you MUST call cxTreeIteratorDispose() manually to release
269 * the memory.
270 *
271 * @remark At the moment, the returned iterator does not support cxIteratorFlagRemoval().
272 *
273 * @param root the root node
274 * @param passes the passes this iterator shall perform
275 * @param loc_children offset in the node struct for the children linked list
276 * @param loc_next offset in the node struct for the next pointer
277 * @return the new tree iterator
278 * @see cxTreeIteratorDispose()
279 */
280 __attribute__((__nonnull__))
281 CxTreeIterator cx_tree_iterate(
282 void const *root,
283 int passes,
284 ptrdiff_t loc_children,
285 ptrdiff_t loc_next
286 );
288 #ifdef __cplusplus
289 } // extern "C"
290 #endif
292 #endif //UCX_TREE_H