misc/insremque.c

   1 /* Copyright (C) 1992-2020 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <stddef.h>
  19 #include <search.h>
  20
  21 /* Insert ELEM into a doubly-linked list, after PREV.  */
  22
  23 void
  24 insque (void *elem, void *prev)
  25 {
  26   if (prev == NULL)
  27     {
  28       ((struct qelem *) elem)->q_forw = NULL;
  29       ((struct qelem *) elem)->q_back = NULL;
  30     }
  31   else
  32     {
  33       struct qelem *next = ((struct qelem *) prev)->q_forw;
  34       ((struct qelem *) prev)->q_forw = (struct qelem *) elem;
  35       if (next != NULL)
  36         next->q_back = (struct qelem *) elem;
  37       ((struct qelem *) elem)->q_forw = next;
  38       ((struct qelem *) elem)->q_back = (struct qelem *) prev;
  39     }
  40 }
  41
  42 /* Unlink ELEM from the doubly-linked list that it is in.  */
  43
  44 void
  45 remque (void *elem)
  46 {
  47   struct qelem *next = ((struct qelem *) elem)->q_forw;
  48   struct qelem *prev = ((struct qelem *) elem)->q_back;
  49   if (next != NULL)
  50     next->q_back = prev;
  51   if (prev != NULL)
  52     prev->q_forw = (struct qelem *) next;
  53 }