Added a straigtforward implementation of circular linked lists. They are

a small bit less efficient than our lists.h lists (testing against zero is
faster than testing against list head), but they are nicer and they save
one pointer per list head which makes them better for hash tables etc.

diff --git a/lib/clists.h b/lib/clists.h
new file mode 100644 (file)
index 0000000..e9826eb
--- /dev/null
+++ b/lib/clists.h
@@ -0,0 +1,76 @@
+/*
+ *     Sherlock Library -- Circular Linked Lists
+ *
+ *     (c) 2003 Martin Mares <mj@ucw.cz>
+ *
+ *     This software may be freely distributed and used according to the terms
+ *     of the GNU Lesser General Public License.
+ */
+
+#ifndef _SHERLOCK_CLISTS_H
+#define _SHERLOCK_CLISTS_H
+
+typedef struct cnode {
+  struct cnode *next, *prev;
+} cnode;
+
+typedef struct clist {
+  struct cnode head;
+} clist;
+
+static inline void *clist_head(clist *l)
+{
+  return (l->head.next != &l->head) ? l->head.next : NULL;
+}
+
+static inline void *clist_tail(clist *l)
+{
+  return (l->head.prev != &l->head) ? l->head.prev : NULL;
+}
+
+static inline void *clist_next(clist *l, cnode *n)
+{
+  return (n->next != &l->head) ? (void *) n->next : NULL;
+}
+
+static inline void *clist_prev(clist *l, cnode *n)
+{
+  return (n->prev != &l->head) ? (void *) n->prev : NULL;
+}
+
+#define CLIST_WALK(n,list) for(n=(void*)(list).head.next; (cnode*)(n) != &(list).head; n=(void*)((cnode*)(n))->next)
+
+static inline void clist_insert(cnode *what, cnode *after)
+{
+  cnode *before = after->next;
+  what->next = before;
+  what->prev = before->prev;
+  before->prev = what;
+  after->next = what;
+}
+
+static inline void clist_add_tail(clist *l, cnode *n)
+{
+  clist_insert(n, l->head.prev);
+}
+
+static inline void clist_add_head(clist *l, cnode *n)
+{
+  clist_insert(n, &l->head);
+}
+
+static inline void clist_remove(cnode *n)
+{
+  cnode *before = n->prev;
+  cnode *after = n->next;
+  before->next = after;
+  after->prev = before;
+}
+
+static inline void clist_init(clist *l)
+{
+  cnode *head = &l->head;
+  head->next = head->prev = head;
+}
+
+#endif