1 /* insque(3C) routines
2    This file is in the public domain.  */
3 
4 /*
5 
6 @deftypefn Supplemental void insque (struct qelem *@var{elem}, @
7   struct qelem *@var{pred})
8 @deftypefnx Supplemental void remque (struct qelem *@var{elem})
9 
10 Routines to manipulate queues built from doubly linked lists.  The
11 @code{insque} routine inserts @var{elem} in the queue immediately
12 after @var{pred}.  The @code{remque} routine removes @var{elem} from
13 its containing queue.  These routines expect to be passed pointers to
14 structures which have as their first members a forward pointer and a
15 back pointer, like this prototype (although no prototype is provided):
16 
17 @example
18 struct qelem @{
19   struct qelem *q_forw;
20   struct qelem *q_back;
21   char q_data[];
22 @};
23 @end example
24 
25 @end deftypefn
26 
27 */
28 
29 
30 struct qelem {
31   struct qelem *q_forw;
32   struct qelem *q_back;
33 };
34 
35 
36 void
insque(struct qelem * elem,struct qelem * pred)37 insque (struct qelem *elem, struct qelem *pred)
38 {
39   elem -> q_forw = pred -> q_forw;
40   pred -> q_forw -> q_back = elem;
41   elem -> q_back = pred;
42   pred -> q_forw = elem;
43 }
44 
45 
46 void
remque(struct qelem * elem)47 remque (struct qelem *elem)
48 {
49   elem -> q_forw -> q_back = elem -> q_back;
50   elem -> q_back -> q_forw = elem -> q_forw;
51 }
52