diff -r 1f40ca07ae1b -r 839fefbdedc7 ucx/tree.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ucx/tree.c	Thu May 23 22:35:45 2024 +0200
@@ -0,0 +1,401 @@
+/*
+ * 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 "cx/array_list.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;
+}
+
+int cx_tree_search(
+        void const *root,
+        void const *data,
+        cx_tree_search_func sfunc,
+        void **result,
+        ptrdiff_t loc_children,
+        ptrdiff_t loc_next
+) {
+    int ret;
+    *result = NULL;
+
+    // shortcut: compare root before doing anything else
+    ret = sfunc(root, data);
+    if (ret < 0) {
+        return ret;
+    } else if (ret == 0 || tree_children(root) == NULL) {
+        *result = (void*)root;
+        return ret;
+    }
+
+    // create a working stack
+    CX_ARRAY_DECLARE(void const*, work);
+    cx_array_initialize(work, 32);
+
+    // add the children of root to the working stack
+    {
+        void *c = tree_children(root);
+        while (c != NULL) {
+            cx_array_simple_add(work, c);
+            c = tree_next(c);
+        }
+    }
+
+    // remember a candidate for adding the data
+    // also remember the exact return code from sfunc
+    void *candidate = NULL;
+    int ret_candidate = -1;
+
+    // process the working stack
+    while (work_size > 0) {
+        // pop element
+        void const *node = work[--work_size];
+
+        // apply the search function
+        ret = sfunc(node, data);
+
+        if (ret == 0) {
+            // if found, exit the search
+            *result = (void*) node;
+            work_size = 0;
+            break;
+        } else if (ret > 0) {
+            // if children might contain the data, add them to the stack
+            void *c = tree_children(node);
+            while (c != NULL) {
+                cx_array_simple_add(work, c);
+                c = tree_next(c);
+            }
+
+            // remember this node in case no child is suitable
+            if (ret_candidate < 0 || ret < ret_candidate) {
+                candidate = (void *) node;
+                ret_candidate = ret;
+            }
+        }
+    }
+
+    // not found, but was there a candidate?
+    if (ret != 0 && candidate != NULL) {
+        ret = ret_candidate;
+        *result = candidate;
+    }
+
+    // free the working queue and return
+    free(work);
+    return ret;
+}
+
+static bool cx_tree_iter_valid(void const *it) {
+    struct cx_tree_iterator_s const *iter = it;
+    return iter->node != NULL;
+}
+
+static void *cx_tree_iter_current(void const *it) {
+    struct cx_tree_iterator_s const *iter = it;
+    return iter->node;
+}
+
+static void cx_tree_iter_next(void *it) {
+    struct cx_tree_iterator_s *iter = it;
+    ptrdiff_t const loc_next = iter->loc_next;
+    ptrdiff_t const loc_children = iter->loc_children;
+
+    void *children;
+
+    // check if we are currently exiting or entering nodes
+    if (iter->exiting) {
+        children = NULL;
+        // skipping on exit is pointless, just clear the flag
+        iter->skip = false;
+    } else {
+        if (iter->skip) {
+            // skip flag is set, pretend that there are no children
+            iter->skip = false;
+            children = NULL;
+        } else {
+            // try to enter the children (if any)
+            children = tree_children(iter->node);
+        }
+    }
+
+    if (children == NULL) {
+        // search for the next node
+        void *next;
+        cx_tree_iter_search_next:
+        // check if there is a sibling
+        if (iter->exiting) {
+            next = iter->node_next;
+        } else {
+            next = tree_next(iter->node);
+            iter->node_next = next;
+        }
+        if (next == NULL) {
+            // no sibling, we are done with this node and exit
+            if (iter->visit_on_exit && !iter->exiting) {
+                // iter is supposed to visit the node again
+                iter->exiting = true;
+            } else {
+                iter->exiting = false;
+                if (iter->depth == 1) {
+                    // there is no parent - we have iterated the entire tree
+                    // invalidate the iterator and free the node stack
+                    iter->node = iter->node_next = NULL;
+                    iter->stack_capacity = iter->depth = 0;
+                    free(iter->stack);
+                    iter->stack = NULL;
+                } else {
+                    // the parent node can be obtained from the top of stack
+                    // this way we can avoid the loc_parent in the iterator
+                    iter->depth--;
+                    iter->node = iter->stack[iter->depth - 1];
+                    // retry with the parent node to find a sibling
+                    goto cx_tree_iter_search_next;
+                }
+            }
+        } else {
+            if (iter->visit_on_exit && !iter->exiting) {
+                // iter is supposed to visit the node again
+                iter->exiting = true;
+            } else {
+                iter->exiting = false;
+                // move to the sibling
+                iter->counter++;
+                iter->node = next;
+                // new top of stack is the sibling
+                iter->stack[iter->depth - 1] = next;
+            }
+        }
+    } else {
+        // node has children, push the first child onto the stack and enter it
+        cx_array_simple_add(iter->stack, children);
+        iter->node = children;
+        iter->counter++;
+    }
+}
+
+CxTreeIterator cx_tree_iterator(
+        void *root,
+        bool visit_on_exit,
+        ptrdiff_t loc_children,
+        ptrdiff_t loc_next
+) {
+    CxTreeIterator iter;
+    iter.loc_children = loc_children;
+    iter.loc_next = loc_next;
+    iter.visit_on_exit = visit_on_exit;
+
+    // allocate stack
+    iter.stack_capacity = 16;
+    iter.stack = malloc(sizeof(void *) * 16);
+    iter.depth = 0;
+
+    // visit the root node
+    iter.node = root;
+    iter.node_next = NULL;
+    iter.counter = 1;
+    iter.depth = 1;
+    iter.stack[0] = root;
+    iter.exiting = false;
+    iter.skip = false;
+
+    // assign base iterator functions
+    iter.base.mutating = false;
+    iter.base.remove = false;
+    iter.base.current_impl = NULL;
+    iter.base.valid = cx_tree_iter_valid;
+    iter.base.next = cx_tree_iter_next;
+    iter.base.current = cx_tree_iter_current;
+
+    return iter;
+}
+
+static bool cx_tree_visitor_valid(void const *it) {
+    struct cx_tree_visitor_s const *iter = it;
+    return iter->node != NULL;
+}
+
+static void *cx_tree_visitor_current(void const *it) {
+    struct cx_tree_visitor_s const *iter = it;
+    return iter->node;
+}
+
+__attribute__((__nonnull__))
+static void cx_tree_visitor_enqueue_siblings(
+        struct cx_tree_visitor_s *iter, void *node, ptrdiff_t loc_next) {
+    node = tree_next(node);
+    while (node != NULL) {
+        struct cx_tree_visitor_queue_s *q;
+        q = malloc(sizeof(struct cx_tree_visitor_queue_s));
+        q->depth = iter->queue_last->depth;
+        q->node = node;
+        iter->queue_last->next = q;
+        iter->queue_last = q;
+        node = tree_next(node);
+    }
+    iter->queue_last->next = NULL;
+}
+
+static void cx_tree_visitor_next(void *it) {
+    struct cx_tree_visitor_s *iter = it;
+    ptrdiff_t const loc_next = iter->loc_next;
+    ptrdiff_t const loc_children = iter->loc_children;
+
+    // add the children of the current node to the queue
+    // unless the skip flag is set
+    void *children;
+    if (iter->skip) {
+        iter->skip = false;
+        children = NULL;
+    } else {
+        children = tree_children(iter->node);
+    }
+    if (children != NULL) {
+        struct cx_tree_visitor_queue_s *q;
+        q = malloc(sizeof(struct cx_tree_visitor_queue_s));
+        q->depth = iter->depth + 1;
+        q->node = children;
+        if (iter->queue_last == NULL) {
+            assert(iter->queue_next == NULL);
+            iter->queue_next = q;
+        } else {
+            iter->queue_last->next = q;
+        }
+        iter->queue_last = q;
+        cx_tree_visitor_enqueue_siblings(iter, children, loc_next);
+    }
+
+    // check if there is a next node
+    if (iter->queue_next == NULL) {
+        iter->node = NULL;
+        return;
+    }
+
+    // dequeue the next node
+    iter->node = iter->queue_next->node;
+    iter->depth = iter->queue_next->depth;
+    {
+        struct cx_tree_visitor_queue_s *q = iter->queue_next;
+        iter->queue_next = q->next;
+        if (iter->queue_next == NULL) {
+            assert(iter->queue_last == q);
+            iter->queue_last = NULL;
+        }
+        free(q);
+    }
+
+    // increment the node counter
+    iter->counter++;
+}
+
+CxTreeVisitor cx_tree_visitor(
+        void *root,
+        ptrdiff_t loc_children,
+        ptrdiff_t loc_next
+) {
+    CxTreeVisitor iter;
+    iter.loc_children = loc_children;
+    iter.loc_next = loc_next;
+
+    // allocate stack
+    iter.depth = 0;
+
+    // visit the root node
+    iter.node = root;
+    iter.counter = 1;
+    iter.depth = 1;
+    iter.skip = false;
+    iter.queue_next = NULL;
+    iter.queue_last = NULL;
+
+    // assign base iterator functions
+    iter.base.mutating = false;
+    iter.base.remove = false;
+    iter.base.current_impl = NULL;
+    iter.base.valid = cx_tree_visitor_valid;
+    iter.base.next = cx_tree_visitor_next;
+    iter.base.current = cx_tree_visitor_current;
+
+    return iter;
+}
+