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
      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
      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  }