diff -r b0c4750cecd8 -r 425234b05dff src/tree.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/tree.c	Mon Jan 22 19:34:38 2024 +0100
@@ -0,0 +1,87 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
+ *
+ * Copyright 2024 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 <assert.h>
+
+#define CX_TREE_PTR(cur, off) (*(void**)(((char*)(cur))+(off)))
+#define CX_TREE_PTR(cur, off) (*(void**)(((char*)(cur))+(off)))
+#define tree_parent(node) CX_TREE_PTR(node, loc_parent)
+#define tree_children(node) CX_TREE_PTR(node, loc_children)
+#define tree_prev(node) CX_TREE_PTR(node, loc_prev)
+#define tree_next(node) CX_TREE_PTR(node, loc_next)
+
+void cx_tree_link(
+        void *restrict parent,
+        void *restrict node,
+        ptrdiff_t loc_parent,
+        ptrdiff_t loc_children,
+        ptrdiff_t loc_prev,
+        ptrdiff_t loc_next
+) {
+    void *current_parent = tree_parent(node);
+    if (current_parent == parent) return;
+    if (current_parent != NULL) {
+        cx_tree_unlink(node, loc_parent, loc_children,
+                       loc_prev, loc_next);
+    }
+
+    if (tree_children(parent) == NULL) {
+        tree_children(parent) = node;
+    } else {
+        void *children = tree_children(parent);
+        tree_prev(children) = node;
+        tree_next(node) = children;
+        tree_children(parent) = node;
+    }
+    tree_parent(node) = parent;
+}
+
+void cx_tree_unlink(
+        void *node,
+        ptrdiff_t loc_parent,
+        ptrdiff_t loc_children,
+        ptrdiff_t loc_prev,
+        ptrdiff_t loc_next
+) {
+    if (tree_parent(node) == NULL) return;
+
+    void *left = tree_prev(node);
+    void *right = tree_next(node);
+    assert(left == NULL || tree_children(tree_parent(node)) != node);
+    if (left == NULL) {
+        tree_children(tree_parent(node)) = right;
+    } else {
+        tree_next(left) = right;
+    }
+    if (right != NULL) tree_prev(right) = left;
+    tree_parent(node) = NULL;
+    tree_prev(node) = NULL;
+    tree_next(node) = NULL;
+}