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 faad86f5c736a3a53ed08c79e74f92c39086a810..03614873ef6a718aaaadec32a27356f82c6c7912 100644 (file)
--- a/ccan/list/list.h
+++ b/ccan/list/list.h
@@ -292,6 +292,34 @@ static inline const void *list_top_(const struct list_head *h, size_t off)
        return (const char *)h->n.next - off;
 }
 
+/**
+ * list_pop - remove the first entry in a list
+ * @h: the list_head
+ * @type: the type of the entry
+ * @member: the list_node member of the type
+ *
+ * If the list is empty, returns NULL.
+ *
+ * Example:
+ *     struct child *one;
+ *     one = list_pop(&parent->children, struct child, list);
+ *     if (!one)
+ *             printf("Empty list!\n");
+ */
+#define list_pop(h, type, member)                                      \
+       ((type *)list_pop_((h), list_off_(type, member)))
+
+static inline const void *list_pop_(const struct list_head *h, size_t off)
+{
+       struct list_node *n;
+
+       if (list_empty(h))
+               return NULL;
+       n = h->n.next;
+       list_del(n);
+       return (const char *)n - off;
+}
+
 /**
  * list_tail - get the last entry in a list
  * @h: the list_head
@@ -371,6 +399,105 @@ 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
+ * @from: the list to empty.
+ *
+ * This takes the entire contents of @from and moves it to the end of
+ * @to.  After this @from will be empty.
+ *
+ * Example:
+ *     struct list_head adopter;
+ *
+ *     list_append_list(&adopter, &parent->children);
+ *     assert(list_empty(&parent->children));
+ *     parent->num_children = 0;
+ */
+static inline void list_append_list(struct list_head *to,
+                                   struct list_head *from)
+{
+       struct list_node *from_tail = list_debug(from)->n.prev;
+       struct list_node *to_tail = list_debug(to)->n.prev;
+
+       /* Sew in head and entire list. */
+       to->n.prev = from_tail;
+       from_tail->next = &to->n;
+       to_tail->next = &from->n;
+       from->n.prev = to_tail;
+
+       /* Now remove head. */
+       list_del(&from->n);
+       list_head_init(from);
+}
+
+/**
+ * list_prepend_list - empty one list into the start of another.
+ * @to: the list to prepend into
+ * @from: the list to empty.
+ *
+ * This takes the entire contents of @from and moves it to the start
+ * of @to.  After this @from will be empty.
+ *
+ * Example:
+ *     list_prepend_list(&adopter, &parent->children);
+ *     assert(list_empty(&parent->children));
+ *     parent->num_children = 0;
+ */
+static inline void list_prepend_list(struct list_head *to,
+                                    struct list_head *from)
+{
+       struct list_node *from_tail = list_debug(from)->n.prev;
+       struct list_node *to_head = list_debug(to)->n.next;
+
+       /* Sew in head and entire list. */
+       to->n.next = &from->n;
+       from->n.prev = &to->n;
+       to_head->prev = from_tail;
+       from_tail->next = to_head;
+
+       /* Now remove head. */
+       list_del(&from->n);
+       list_head_init(from);
+}
+
 /**
  * list_for_each_off - iterate through a list of memory regions.
  * @h: the list_head
@@ -470,4 +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 */