usr/src/lib/libc/port/gen/insque.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26
  27 /*      Copyright (c) 1988 AT&T */
  28 /*        All Rights Reserved   */
  29
  30 #pragma ident   "%Z%%M% %I%     %E% SMI"
  31
  32 /*
  33  * insque() and remque() insert or remove an element from a queue.
  34  * The queue is built from a doubly linked list whose elements are
  35  * defined by a structure where the first member of the structure
  36  * points to the next element in the queue and the second member
  37  * of the structure points to the previous element in the queue.
  38  */
  39
  40 #pragma weak _insque = insque
  41 #pragma weak _remque = remque
  42
  43 #include "lint.h"
  44 #include <sys/types.h>
  45 #include <stdlib.h>
  46 #include <search.h>
  47
  48 void
  49 insque(void *elem, void *pred)
  50 {
  51         if (pred == NULL) {    /* This is the first element being inserted. */
  52                 ((struct qelem *)elem)->q_forw = NULL;
  53                 ((struct qelem *)elem)->q_back = NULL;
  54         } else if (((struct qelem *)pred)->q_forw == NULL) {
  55                                         /* The element is inserted at */
  56                                         /* the end of the queue. */
  57                 ((struct qelem *)elem)->q_forw = NULL;
  58                 ((struct qelem *)elem)->q_back = pred;
  59                 ((struct qelem *)pred)->q_forw = elem;
  60         } else {                /* The element is inserted in the middle of */
  61                                 /* the queue. */
  62                 ((struct qelem *)elem)->q_forw = ((struct qelem *)pred)->q_forw;
  63                 ((struct qelem *)elem)->q_back = pred;
  64                 ((struct qelem *)pred)->q_forw->q_back = elem;
  65                 ((struct qelem *)pred)->q_forw = elem;
  66         }
  67 }
  68
  69 void
  70 remque(void *elem)
  71 {
  72         if (((struct qelem *)elem)->q_back == NULL) {
  73                                         /* The first element is removed. */
  74                 if (((struct qelem *)elem)->q_forw == NULL)
  75                                         /* The only element is removed. */
  76                         return;
  77                 ((struct qelem *)elem)->q_forw->q_back = NULL;
  78         } else if (((struct qelem *)elem)->q_forw == NULL) {
  79                                         /* The last element is removed */
  80                 ((struct qelem *)elem)->q_back->q_forw = NULL;
  81         } else {        /* The middle element is removed. */
  82                 ((struct qelem *)elem)->q_back->q_forw =
  83                     ((struct qelem *)elem)->q_forw;
  84                 ((struct qelem *)elem)->q_forw->q_back =
  85                     ((struct qelem *)elem)->q_back;
  86         }
  87 }