2 files changed, 28 insertions, 4 deletions

diff --git a/list.c b/list.c
index 9cf1ad0..a05aab2 100644
--- a/list.c
+++ b/list.c
@@ -1,4 +1,3 @@
-#include <stddef.h>
 #include "list.h"
 
 struct _list {
@@ -11,6 +10,26 @@ void list_init(struct list *list) {
     list->end = list;
 }
 
+int list_empty(struct list *list) {
+    return list->head == list->end;
+}
+
+int list_singleton(struct list *list) {
+    return list->head == list->tail && list->head != list->end;
+}
+
+void *list_circular_prev(void *_node) {
+    struct _list *node = _node;
+    do { node = node->prev; } while (node == node->listhead);
+    return node;
+}
+
+void *list_circular_next(void *_node) {
+    struct _list *node = _node;
+    do { node = node->next; } while (node == node->listhead);
+    return node;
+}
+
 void list_insert(void *_next, void *_node) {
     struct _list *node = _node;
     struct _list *next = _next;
@@ -19,6 +38,7 @@ void list_insert(void *_next, void *_node) {
     prev->next = node;
     node->next = next;
     node->prev = prev;
+    node->listhead = next->listhead;
 }
 
 void list_remove(void *_node) {
@@ -27,6 +47,4 @@ void list_remove(void *_node) {
     struct _list *prev = node->prev;
     next->prev = prev;
     prev->next = next;
-    node->next = NULL;
-    node->prev = NULL;
 }
diff --git a/list.h b/list.h
index 7d7a272..2bfa1e1 100644
--- a/list.h
+++ b/list.h
@@ -1,10 +1,16 @@
 #pragma once
-#define LINKEDLIST void *prev, *next
+#define LINKEDLIST void *prev, *next, *listhead
 
 struct list {
     void *tail, *head, *end;
 };
 
 extern void list_init(struct list *list);
+extern int list_empty(struct list *list);
+extern int list_singleton(struct list *list);
+
+extern void *list_circular_prev(void *_node);
+extern void *list_circular_next(void *_node);
+
 extern void list_insert(void *_next, void *_node);
 extern void list_remove(void *_node);