1 files changed, 107 insertions, 0 deletions
diff --git a/Include/internal/pycore_llist.h b/Include/internal/pycore_llist.h
new file mode 100644
index 0000000..5fd261d
--- /dev/null
+++ b/Include/internal/pycore_llist.h
@@ -0,0 +1,107 @@
+// A doubly-linked list that can be embedded in a struct.
+//
+// Usage:
+//  struct llist_node head = LLIST_INIT(head);
+//  typedef struct {
+//      ...
+//      struct llist_node node;
+//      ...
+//  } MyObj;
+//
+//  llist_insert_tail(&head, &obj->node);
+//  llist_remove(&obj->node);
+//
+//  struct llist_node *node;
+//  llist_for_each(node, &head) {
+//      MyObj *obj = llist_data(node, MyObj, node);
+//      ...
+//  }
+//
+
+#ifndef Py_INTERNAL_LLIST_H
+#define Py_INTERNAL_LLIST_H
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "Py_BUILD_CORE must be defined to include this header"
+#endif
+
+struct llist_node {
+    struct llist_node *next;
+    struct llist_node *prev;
+};
+
+// Get the struct containing a node.
+#define llist_data(node, type, member) \
+    (type*)((char*)node - offsetof(type, member))
+
+// Iterate over a list.
+#define llist_for_each(node, head) \
+    for (node = (head)->next; node != (head); node = node->next)
+
+// Iterate over a list, but allow removal of the current node.
+#define llist_for_each_safe(node, head) \
+    for (struct llist_node *_next = (node = (head)->next, node->next); \
+         node != (head); node = _next, _next = node->next)
+
+#define LLIST_INIT(head) { &head, &head }
+
+static inline void
+llist_init(struct llist_node *head)
+{
+    head->next = head;
+    head->prev = head;
+}
+
+// Returns 1 if the list is empty, 0 otherwise.
+static inline int
+llist_empty(struct llist_node *head)
+{
+    return head->next == head;
+}
+
+// Appends to the tail of the list.
+static inline void
+llist_insert_tail(struct llist_node *head, struct llist_node *node)
+{
+    node->prev = head->prev;
+    node->next = head;
+    head->prev->next = node;
+    head->prev = node;
+}
+
+// Remove a node from the list.
+static inline void
+llist_remove(struct llist_node *node)
+{
+    struct llist_node *prev = node->prev;
+    struct llist_node *next = node->next;
+    prev->next = next;
+    next->prev = prev;
+    node->prev = NULL;
+    node->next = NULL;
+}
+
+// Append all nodes from head2 onto head1. head2 is left empty.
+static inline void
+llist_concat(struct llist_node *head1, struct llist_node *head2)
+{
+    if (!llist_empty(head2)) {
+        head1->prev->next = head2->next;
+        head2->next->prev = head1->prev;
+
+        head1->prev = head2->prev;
+        head2->prev->next = head1;
+        llist_init(head2);
+    }
+}
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_LLIST_H */