diff -r 809581724cc7 -r 0358f1d9c506 ucx/tree.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ucx/tree.c	Mon May 22 16:17:26 2023 +0200
@@ -0,0 +1,52 @@
+/*
+ * 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.
+ */
+
+#include "cx/tree.h"
+#include "cx/linked_list.h"
+
+#define CX_TR_PTR(cur, off) *((void**)(((char*)(cur))+(off)))
+
+void cx_tree_add_sibling(void *node, ptrdiff_t loc_prev, ptrdiff_t loc_next, ptrdiff_t loc_parent, void *new_node) {
+    cx_linked_list_add(&node, NULL, loc_prev, loc_next, new_node);
+
+    // optional parent link
+    if (loc_parent >= 0) {
+        CX_TR_PTR(new_node, loc_parent) = CX_TR_PTR(node, loc_parent);
+    }
+}
+
+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) {
+    cx_linked_list_add(children_begin, children_end, loc_prev, loc_next, new_node);
+
+    // optional parent link
+    if (loc_parent >= 0) {
+        CX_TR_PTR(new_node, loc_parent) = parent;
+    }
+}