feat: add ListNode

include/list.h

@@ -0,0 +1,43 @@
+#ifndef FROSTBYTE_LIST_H
+#define FROSTBYTE_LIST_H
+
+#include "types.h"
+#include <stddef.h>
+
+/*
+ * List: an intrusive circular doubly-linked list, Linux-kernel style. The
+ * list head and every node share the same ListNode type; a sentinel node
+ * (passed to listInit) acts as both head and tail so insert/remove never
+ * need a null check. Embed a ListNode in your own struct and use
+ * listEntry() to recover the containing struct pointer -- no allocation,
+ * no element copying, just pointer relinking.
+ */
+
+typedef struct ListNode {
+    struct ListNode* next;
+    struct ListNode* prev;
+} ListNode;
+
+#define listEntry(ptr, type, member) \
+    ((type*)((uint8*)(ptr) - offsetof(type, member)))
+
+#define listForEach(cursor, head) \
+    for ((cursor) = (head)->next; (cursor) != (head); (cursor) = (cursor)->next)
+
+void listInit(ListNode* head);
+bool listEmpty(const ListNode* head);
+
+void listInsertAfter(ListNode* pos, ListNode* newNode);
+void listInsertBefore(ListNode* pos, ListNode* newNode);
+void listPushBack(ListNode* head, ListNode* newNode);
+void listPushFront(ListNode* head, ListNode* newNode);
+
+/* Unlinks node from whatever list it is in. Safe to call again on an
+   already-removed node (it becomes its own trivial one-element list). */
+void listRemove(ListNode* node);
+
+usize listLen(const ListNode* head);
+ListNode* listFront(const ListNode* head);
+ListNode* listBack(const ListNode* head);
+
+#endif