diff -r 99a34860c105 -r d938228c382e src/ucx/cx/tree.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ucx/cx/tree.h	Sun Nov 06 15:53:32 2022 +0100
@@ -0,0 +1,136 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
+ *
+ * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+/**
+ * \file tree.h
+ * \brief Interface for tree implementations.
+ * \author Olaf Wintermann
+ * \author Mike Becker
+ * \version 3.0
+ * \copyright 2-Clause BSD License
+ */
+
+#ifndef UCX_TREE_H
+#define UCX_TREE_H
+
+#include "common.h"
+#include "allocator.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Adds a sibling to the current tree node.
+ *
+ * In case your struct does not have a \p prev or a \p parent pointer,
+ * specify a negative location. The location of the \p next pointer is
+ * mandatory.
+ *
+ * \attention Do not use this function to add siblings in a tree where the
+ * nodes store a pointer to the last sibling because that would not be modified by this function.
+ *
+ * \remark If yo do not provide a location to the parent pointer, a call to this function is
+ * effectively the same as a call to cx_linked_list_add().
+ *
+ * @param node a pointer to the node
+ * @param loc_prev the location of a \c prev pointer within your node struct
+ * @param loc_next the location of a \c next pointer within your node struct
+ * @param loc_parent the location of a \c parent pointer within your node struct
+ * @param new_node the new node that shall be added as a sibling
+ */
+void cx_tree_add_sibling(void *node,
+                         ptrdiff_t loc_prev, ptrdiff_t loc_next,
+                         ptrdiff_t loc_parent,
+                         void *new_node)
+__attribute__((__nonnull__));
+
+/**
+ * Adds a node to the list of children.
+ *
+ * \par Example with a full structure
+ * A full tree node structure may look like this:
+ * \code
+ * typedef struct MyTreeNode MyTreeNode;
+ * struct MyTreeNode {
+ *   MyTreeNode* parent;
+ *   MyTreeNode* first_child;
+ *   MyTreeNode* last_child;
+ *   MyTreeNode* prev_sibling;
+ *   MyTreeNode* next_sibling;
+ *   // ...contents...
+ * }
+ * \endcode
+ * Adding a new child to a node with the above structure can be performed with the following call:
+ * \code
+ * MyTreeNode *node, *child; // given
+ * cx_tree_add_child(&node->first_child, &node->last_child,
+ *                   offsetof(MyTreeNode, prev_sibling), offsetof(MyTreeNode, next_sibling),
+ *                   child, offsetof(MyTreeNode, parent), node);
+ * \endcode
+ *
+ * \par Example with a reduced structure
+ * The minimal reasonable structure with parent pointer looks like this:
+ * \code
+ * typedef struct MyTreeNode MyTreeNode;
+ * struct MyTreeNode {
+ *   MyTreeNode* parent;
+ *   MyTreeNode* children;
+ *   MyTreeNode* next_sibling;
+ *   // ...contents...
+ * }
+ * \endcode
+ * This simplifies the function call to:
+ * \code
+ * MyTreeNode *node, *child; // given
+ * cx_tree_add_child(&node->children, NULL, -1, offsetof(MyTreeNode, next_sibling),
+ *                   child, offsetof(MyTreeNode, parent), node);
+ * \endcode
+ *
+ * \remark If your tree structure does not possess a parent pointer, a call to this function is
+ * effectively the same as a call to cx_linked_list_add().
+ *
+ * @param children_begin a pointer to the begin node pointer (if your list has one)
+ * @param children_end a pointer to the end node pointer (if your list has one)
+ * @param loc_prev the location of a \c prev pointer within your node struct
+ * @param loc_next the location of a \c next pointer within your node struct
+ * @param new_node a pointer to the node that shall be appended
+ * @param loc_parent the location of a \c parent pointer within your node struct
+ * @param parent the parent node
+ */
+void cx_tree_add_child(void **children_begin, void **children_end,
+                       ptrdiff_t loc_prev, ptrdiff_t loc_next, void *new_node,
+                       ptrdiff_t loc_parent, void *parent)
+__attribute__((__nonnull__ (5)));
+
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* UCX_TREE_H */
+