1 /*
2  * Copyright (c) 1988, 1989, 1990 The Regents of the University of California.
3  * All rights reserved.
4  *
5  * This code is derived from software contributed to Berkeley by
6  * Adam de Boor.
7  *
8  * Redistribution and use in source and binary forms are permitted
9  * provided that the above copyright notice and this paragraph are
10  * duplicated in all such forms and that any documentation,
11  * advertising materials, and other materials related to such
12  * distribution and use acknowledge that the software was developed
13  * by the University of California, Berkeley.  The name of the
14  * University may not be used to endorse or promote products derived
15  * from this software without specific prior written permission.
16  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
17  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
18  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
19  */
20 
21 #ifndef lint
22 static char sccsid[] = "@(#)lstSetCirc.c	5.2 (Berkeley) 03/11/90";
23 #endif /* not lint */
24 
25 /*-
26  * listSetCirc.c --
27  *	Change the library's notion of the circularity of a list.
28  */
29 
30 #include	"lstInt.h"
31 
32 /*
33  *------------------------------------------------------------
34  * Lst_SetCirc --
35  *	change the circularity of a list
36  *
37  * Results:
38  *	none
39  *
40  * Side Effects:
41  *	The circularity of the list is set appropriately. The head and
42  *	tail of the list will be linked or unlinked as necessary
43  *------------------------------------------------------------
44  */
45 void
46 Lst_SetCirc (l, circ)
47     Lst	    	  l;
48     Boolean	  circ;
49 {
50     register List list = (List) l;
51 
52     /*
53      * if this isn't a change, do nothing.
54      */
55     if ((list->isCirc && circ) || (!list->isCirc && !circ)) {
56 	return;
57     }
58     list->isCirc = circ;
59 
60     if (LstIsEmpty (l)) {
61 	return;
62     }
63 
64     if (circ) {
65 	list->firstPtr->prevPtr = list->lastPtr;
66 	list->lastPtr->nextPtr = list->firstPtr;
67     } else {
68 	list->firstPtr->prevPtr = NilListNode;
69 	list->lastPtr->nextPtr = NilListNode;
70     }
71 }
72