source/ubiqx/ubi_sLinkList.c

   1 /* ========================================================================== **
   2  *                              ubi_sLinkList.c
   3  *
   4  *  Copyright (C) 1997, 1998 by Christopher R. Hertel
   5  *
   6  *  Email: crh@ubiqx.mn.org
   7  * -------------------------------------------------------------------------- **
   8  *  This module implements a simple singly-linked list.
   9  * -------------------------------------------------------------------------- **
  10  *
  11  *  This library is free software; you can redistribute it and/or
  12  *  modify it under the terms of the GNU Library General Public
  13  *  License as published by the Free Software Foundation; either
  14  *  version 2 of the License, or (at your option) any later version.
  15  *
  16  *  This library is distributed in the hope that it will be useful,
  17  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  *  Library General Public License for more details.
  20  *
  21  *  You should have received a copy of the GNU Library General Public
  22  *  License along with this library; if not, write to the Free
  23  *  Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  24  *
  25  * -------------------------------------------------------------------------- **
  26  *
  27  * Log: ubi_sLinkList.c,v
  28  * Revision 0.10  1999/06/19 16:58:06  crh
  29  * Renamed the ubi_slRemove() function in ubi_sLinkList to
  30  * ubi_slRemoveNext().  I was bothered by the fact that it didn't
  31  * match the functionality of the ubi_dlRemove() function in
  32  * ubi_dLinkList.  The new name is more 'correct'.
  33  *
  34  * Revision 0.9  1998/07/24 07:30:20  crh
  35  * Added the ubi_slNewList() macro.
  36  *
  37  * Revision 0.8  1998/06/04 21:29:27  crh
  38  * Upper-cased defined constants (eg UBI_BINTREE_H) in some header files.
  39  * This is more "standard", and is what people expect.  Weird, eh?
  40  *
  41  * Revision 0.7  1998/06/03 18:06:03  crh
  42  * Further fiddling with sys_include.h, which has been moved from the .c file
  43  * to the .h file.
  44  *
  45  * Revision 0.6  1998/06/02 01:38:47  crh
  46  * Changed include file name from ubi_null.h to sys_include.h to make it
  47  * more generic.
  48  *
  49  * Revision 0.5  1998/05/20 04:38:05  crh
  50  * The C file now includes ubi_null.h.  See ubi_null.h for more info.
  51  *
  52  * Revision 0.4  1998/03/10 02:23:20  crh
  53  * Combined ubi_StackQueue and ubi_sLinkList into one module.  Redesigned
  54  * the functions and macros.  Not a complete rewrite but close to it.
  55  *
  56  * Revision 0.3  1998/01/03 01:59:52  crh
  57  * Added ubi_slCount() macro.
  58  *
  59  * Revision 0.2  1997/10/21 03:35:18  crh
  60  * Added parameter <After> in function Insert().  Made necessary changes
  61  * to macro AddHead() and added macro AddHere().
  62  *
  63  * Revision 0.1  1997/10/16 02:53:45  crh
  64  * Initial Revision.
  65  *
  66  * -------------------------------------------------------------------------- **
  67  *  This module implements a singly-linked list which may also be used as a
  68  *  queue or a stack.  For a queue, entries are added at the tail and removed
  69  *  from the head of the list.  For a stack, the entries are entered and
  70  *  removed from the head of the list.  A traversal of the list will always
  71  *  start at the head of the list and proceed toward the tail.  This is all
  72  *  mind-numbingly simple, but I'm surprised by the number of programs out
  73  *  there which re-implement this a dozen or so times.
  74  *
  75  *  Note:  When the list header is initialized, the Tail pointer is set to
  76  *         point to the Head pointer.  This simplifies things a great deal,
  77  *         except that you can't initialize a stack or queue by simply
  78  *         zeroing it out.  One sure way to initialize the header is to call
  79  *         ubi_slInit().  Another option would be something like this:
  80  *
  81  *           ubi_slNewList( MyList );
  82  *
  83  *         Which translates to:
  84  *
  85  *           ubi_slList MyList[1] = { NULL, (ubi_slNodePtr)MyList, 0 };
  86  *
  87  *         See ubi_slInit(), ubi_slNewList(), and the ubi_slList structure
  88  *         for more info.
  89  *
  90  *        + Also, note that this module is similar to the ubi_dLinkList
  91  *          module.  There are three key differences:
  92  *          - This is a singly-linked list, the other is a doubly-linked
  93  *            list.
  94  *          - In this module, if the list is empty, the tail pointer will
  95  *            point back to the head of the list as described above.  This
  96  *            is not done in ubi_dLinkList.
  97  *          - The ubi_slRemoveNext() function, by necessity, removes the
  98  *            'next' node.  In ubi_dLinkList, the ubi_dlRemove() function
  99  *            removes the 'current' node.
 100  *
 101  * ========================================================================== **
 102  */
 103
 104 #include "ubi_sLinkList.h"  /* Header for *this* module. */
 105
 106 /* ========================================================================== **
 107  * Functions...
 108  */
 109
 110 ubi_slListPtr ubi_slInitList( ubi_slListPtr ListPtr )
 111   /* ------------------------------------------------------------------------ **
 112    * Initialize a singly-linked list header.
 113    *
 114    *  Input:  ListPtr - A pointer to the list structure that is to be
 115    *                    initialized for use.
 116    *
 117    *  Output: A pointer to the initialized list header (i.e., same as
 118    *          <ListPtr>).
 119    *
 120    * ------------------------------------------------------------------------ **
 121    */
 122   {
 123   ListPtr->Head  = NULL;
 124   ListPtr->Tail  = (ubi_slNodePtr)ListPtr;
 125   ListPtr->count = 0;
 126   return( ListPtr );
 127   } /* ubi_slInitList */
 128
 129 ubi_slNodePtr ubi_slInsert( ubi_slListPtr ListPtr,
 130                             ubi_slNodePtr New,
 131                             ubi_slNodePtr After )
 132   /* ------------------------------------------------------------------------ **
 133    * Add a node to the list.
 134    *
 135    *  Input:  ListPtr - A pointer to the list into which the node is to
 136    *                    be inserted.
 137    *          New     - Pointer to the node that is to be added to the list.
 138    *          After   - Pointer to a list in a node after which the new node
 139    *                    will be inserted.  If NULL, then the new node will
 140    *                    be added at the head of the list.
 141    *
 142    *  Output: A pointer to the node that was inserted into the list (i.e.,
 143    *          the same as <New>).
 144    *
 145    * ------------------------------------------------------------------------ **
 146    */
 147   {
 148   After = After ? After : (ubi_slNodePtr)ListPtr;
 149   New->Next   = After->Next;
 150   After->Next = New;
 151   if( !(New->Next) )
 152     ListPtr->Tail = New;
 153   (ListPtr->count)++;
 154   return( New );
 155   } /* ubi_slInsert */
 156
 157 ubi_slNodePtr ubi_slRemoveNext( ubi_slListPtr ListPtr, ubi_slNodePtr AfterMe )
 158   /* ------------------------------------------------------------------------ **
 159    * Remove the node followng <AfterMe>.  If <AfterMe> is NULL, remove from
 160    * the head of the list.
 161    *
 162    *  Input:  ListPtr - A pointer to the list from which the node is to be
 163    *                    removed.
 164    *          AfterMe - Pointer to the node preceeding the node to be
 165    *                    removed.
 166    *
 167    *  Output: A pointer to the node that was removed, or NULL if the list is
 168    *          empty.
 169    *
 170    * ------------------------------------------------------------------------ **
 171    */
 172   {
 173   ubi_slNodePtr DelNode;
 174
 175   AfterMe = AfterMe ? AfterMe : (ubi_slNodePtr)ListPtr;
 176   DelNode = AfterMe->Next;
 177   if( DelNode )
 178     {
 179     if( !(DelNode->Next) )
 180       ListPtr->Tail = AfterMe;
 181     AfterMe->Next  = DelNode->Next;
 182     (ListPtr->count)--;
 183     }
 184   return( DelNode );
 185   } /* ubi_slRemoveNext */
 186
 187 /* ================================ The End ================================= */