5  *  Intended to work with a list sentinal which is created as an empty
6  *  list.  Insert & delete are O(1).
50  * Remove an element from list.
62  * Insert an element to the list head.
64  * \param list list.
67 #define insert_at_head(list, elem)		\  argument
69    (elem)->prev = list;				\
70    (elem)->next = (list)->next;			\
71    (list)->next->prev = elem;			\
72    (list)->next = elem;				\
76  * Insert an element to the list tail.
78  * \param list list.
81 #define insert_at_tail(list, elem)		\  argument
83    (elem)->next = list;				\
84    (elem)->prev = (list)->prev;			\
85    (list)->prev->next = elem;			\
86    (list)->prev = elem;				\
90  * Move an element to the list head.
92  * \param list list.
95 #define move_to_head(list, elem)		\  argument
98    insert_at_head(list, elem);			\
102  * Move an element to the list tail.
104  * \param list list.
107 #define move_to_tail(list, elem)		\  argument
110    insert_at_tail(list, elem);			\
114  * Make a empty list empty.
116  * \param sentinal list (sentinal element).
125  * Get list first element.
127  * \param list list.
131 #define first_elem(list)       ((list)->next)  argument
134  * Get list last element.
136  * \param list list.
140 #define last_elem(list)        ((list)->prev)  argument
161  * Test whether element is at end of the list.
163  * \param list list.
166  * \return non-zero if element is at end of list, or zero otherwise.
168 #define at_end(list, elem)     ((elem) == (list))  argument
171  * Test if a list is empty.
173  * \param list list.
175  * \return non-zero if list empty, or zero otherwise.
177 #define is_empty_list(list)    ((list)->next == (list))  argument
180  * Walk through the elements of a list.
183  * \param list list.
188 #define foreach(ptr, list)     \  argument
189         for( ptr=(list)->next ;  ptr!=list ;  ptr=(ptr)->next )
192  * Walk through the elements of a list.
194  * Same as #foreach but lets you unlink the current value during a list
195  * traversal.  Useful for freeing a list, element by element.
199  * \param list list.
204 #define foreach_s(ptr, t, list)   \  argument
205         for(ptr=(list)->next,t=(ptr)->next; list != ptr; ptr=t, t=(t)->next)