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
10Routines to manipulate queues built from doubly linked lists.  The
11@code{insque} routine inserts @var{elem} in the queue immediately
12after @var{pred}.  The @code{remque} routine removes @var{elem} from
13its containing queue.  These routines expect to be passed pointers to
14structures which have as their first members a forward pointer and a
15back pointer, like this prototype (although no prototype is provided):
16
17@example
18struct 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
30struct qelem {
31  struct qelem *q_forw;
32  struct qelem *q_back;
33};
34
35
36void
37insque (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
46void
47remque (struct qelem *elem)
48{
49  elem -> q_forw -> q_back = elem -> q_back;
50  elem -> q_back -> q_forw = elem -> q_forw;
51}
52