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