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
110ubi_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
129ubi_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
157ubi_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 ================================= */
188