1/*	$NetBSD: lstNext.c,v 1.12 2008/12/13 15:19:29 dsl Exp $	*/
2
3/*
4 * Copyright (c) 1988, 1989, 1990, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Adam de Boor.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#ifndef MAKE_NATIVE
36static char rcsid[] = "$NetBSD: lstNext.c,v 1.12 2008/12/13 15:19:29 dsl Exp $";
37#else
38#include <sys/cdefs.h>
39#ifndef lint
40#if 0
41static char sccsid[] = "@(#)lstNext.c	8.1 (Berkeley) 6/6/93";
42#else
43__RCSID("$NetBSD: lstNext.c,v 1.12 2008/12/13 15:19:29 dsl Exp $");
44#endif
45#endif /* not lint */
46#endif
47
48/*-
49 * LstNext.c --
50 *	Return the next node for a list.
51 *	The sequential functions access the list in a slightly different way.
52 *	CurPtr points to their idea of the current node in the list and they
53 *	access the list based on it. Because the list is circular, Lst_Next
54 *	and Lst_Prev will go around the list forever. Lst_IsAtEnd must be
55 *	used to determine when to stop.
56 */
57
58#include	"lstInt.h"
59
60/*-
61 *-----------------------------------------------------------------------
62 * Lst_Next --
63 *	Return the next node for the given list.
64 *
65 * Results:
66 *	The next node or NULL if the list has yet to be opened. Also
67 *	if the list is non-circular and the end has been reached, NULL
68 *	is returned.
69 *
70 * Side Effects:
71 *	the curPtr field is updated.
72 *
73 *-----------------------------------------------------------------------
74 */
75LstNode
76Lst_Next(Lst l)
77{
78    ListNode	tln;
79    List 	list = l;
80
81    if ((LstValid (l) == FALSE) ||
82	(list->isOpen == FALSE)) {
83	    return NULL;
84    }
85
86    list->prevPtr = list->curPtr;
87
88    if (list->curPtr == NULL) {
89	if (list->atEnd == Unknown) {
90	    /*
91	     * If we're just starting out, atEnd will be Unknown.
92	     * Then we want to start this thing off in the right
93	     * direction -- at the start with atEnd being Middle.
94	     */
95	    list->curPtr = tln = list->firstPtr;
96	    list->atEnd = Middle;
97	} else {
98	    tln = NULL;
99	    list->atEnd = Tail;
100	}
101    } else {
102	tln = list->curPtr->nextPtr;
103	list->curPtr = tln;
104
105	if (tln == list->firstPtr || tln == NULL) {
106	    /*
107	     * If back at the front, then we've hit the end...
108	     */
109	    list->atEnd = Tail;
110	} else {
111	    /*
112	     * Reset to Middle if gone past first.
113	     */
114	    list->atEnd = Middle;
115	}
116    }
117
118    return (tln);
119}
120
121