DLIST hack

DLIST stands for doubly-circular linked list.

These are defined as follows:

        -------
prev<-- |     | -->next
        -------

They actually point back to themselves, initially.

typedef struct dlist {
   struct dlist * next;
   struct dlist * prev;
} dlist_t;

Some key defines: (dlist is a structure, and newNode is a structure *)

#define DLIST_INIT(dlist) \
   (dlist).next = &(dlist), \
   (dlist).prev = &(dlist)

#define DLIST_ADD2TAIL(dlist,newNode) \
   (newNode)->next = &(dlist), \
   (newNode)->prev = (dlist).prev, \
   (dlist).prev->next = (newNode), \
   (dlist).prev = (newNode);

// Assumes the first element is actually
// dlist.next
#define DLIST_REMOVE_FROM_HEAD(dlist) \
   (dlist).next = (dlist).next->next, \
   (dlist).next->prev = &(dlist);

#define DLIST_REMOVE_FROM_TAIL(dlist) \
   (dlist).prev->prev->next = &(dlist), \
   (dlist).prev = (dlist).prev->prev;

#define DLIST_ADD2HEAD(dlist,newNode) \
   (newNode)->next = (dlist).next, \
   (newNode)->prev = &(dlist), \
   (dlist).next->prev = (newNode), \
   (dlist).next = (newNode);

#define DLIST_ELEMENT(dlist,type,element) \
   ((type *)((char *)&(dlist) - (size_t)offsetof(type,element)))