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/* insque(3C) routines

   This file is in the public domain.  */

/*

@deftypefn Supplemental void insque (struct qelem *@var{elem}, struct qelem *@var{pred})

@deftypefnx Supplemental void remque (struct qelem *@var{elem})

Routines to manipulate queues built from doubly linked lists.  The

@code{insque} routine inserts @var{elem} in the queue immediately

after @var{pred}.  The @code{remque} routine removes @var{elem} from

its containing queue.  These routines expect to be passed pointers to

structures which have as their first members a forward pointer and a

back pointer, like this prototype (although no prototype is provided):

@example

struct qelem @{

  struct qelem *q_forw;

  struct qelem *q_back;

  char q_data[];

@};

@end example

@end deftypefn

*/

struct qelem {

  struct qelem *q_forw;

  struct qelem *q_back;

};

void

insque (struct qelem *elem, struct qelem *pred)

{

  elem -> q_forw = pred -> q_forw;

  pred -> q_forw -> q_back = elem;

  elem -> q_back = pred;

  pred -> q_forw = elem;

}

void

remque (struct qelem *elem)

{

  elem -> q_forw -> q_back = elem -> q_back;

  elem -> q_back -> q_forw = elem -> q_forw;

}