list: add list_next and list_prev helpers.

[ccan] / ccan / list / list.h

diff --git a/ccan/list/list.h b/ccan/list/list.h
index ab3240871773d90ceee149c3cb30931e228326fb..03614873ef6a718aaaadec32a27356f82c6c7912 100644 (file)
--- a/ccan/list/list.h
+++ b/ccan/list/list.h
@@ -399,6 +399,43 @@ static inline const void *list_tail_(const struct list_head *h, size_t off)
 #define list_for_each_safe(h, i, nxt, member)                          \
        list_for_each_safe_off(h, i, nxt, list_off_var_(i, member))
 
+/**
+ * list_next - get the next entry in a list
+ * @h: the list_head
+ * @i: a pointer to an entry in the list.
+ * @member: the list_node member of the structure
+ *
+ * If @i was the last entry in the list, returns NULL.
+ *
+ * Example:
+ *     struct child *second;
+ *     second = list_next(&parent->children, first, list);
+ *     if (!second)
+ *             printf("No second child!\n");
+ */
+#define list_next(h, i, member)                                                \
+       ((list_typeof(i))list_entry_or_null(list_debug(h),              \
+                                           (i)->member.next,           \
+                                           list_off_var_((i), member)))
+
+/**
+ * list_prev - get the previous entry in a list
+ * @h: the list_head
+ * @i: a pointer to an entry in the list.
+ * @member: the list_node member of the structure
+ *
+ * If @i was the first entry in the list, returns NULL.
+ *
+ * Example:
+ *     first = list_prev(&parent->children, second, list);
+ *     if (!first)
+ *             printf("Can't go back to first child?!\n");
+ */
+#define list_prev(h, i, member)                                                \
+       ((list_typeof(i))list_entry_or_null(list_debug(h),              \
+                                           (i)->member.prev,           \
+                                           list_off_var_((i), member)))
+
 /**
  * list_append_list - empty one list onto the end of another.
  * @to: the list to append into
@@ -560,4 +597,19 @@ static inline struct list_node *list_node_from_off_(void *ptr, size_t off)
        (container_off_var(var, member) +               \
         check_type(var->member, struct list_node))
 
+#if HAVE_TYPEOF
+#define list_typeof(var) typeof(var)
+#else
+#define list_typeof(var) void *
+#endif
+
+/* Returns member, or NULL if at end of list. */
+static inline void *list_entry_or_null(struct list_head *h,
+                                      struct list_node *n,
+                                      size_t off)
+{
+       if (n == &h->n)
+               return NULL;
+       return (char *)n - off;
+}
 #endif /* CCAN_LIST_H */