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[] = "@(#)lstNext.c 5.2 (Berkeley) 03/11/90"; 23 #endif /* not lint */ 24 25 /*- 26 * LstNext.c -- 27 * Return the next node for a list. 28 * The sequential functions access the list in a slightly different way. 29 * CurPtr points to their idea of the current node in the list and they 30 * access the list based on it. Because the list is circular, Lst_Next 31 * and Lst_Prev will go around the list forever. Lst_IsAtEnd must be 32 * used to determine when to stop. 33 */ 34 35 #include "lstInt.h" 36 37 /*- 38 *----------------------------------------------------------------------- 39 * Lst_Next -- 40 * Return the next node for the given list. 41 * 42 * Results: 43 * The next node or NILLNODE if the list has yet to be opened. Also 44 * if the list is non-circular and the end has been reached, NILLNODE 45 * is returned. 46 * 47 * Side Effects: 48 * the curPtr field is updated. 49 * 50 *----------------------------------------------------------------------- 51 */ 52 LstNode 53 Lst_Next (l) 54 Lst l; 55 { 56 register ListNode tln; 57 register List list = (List)l; 58 59 if ((LstValid (l) == FALSE) || 60 (list->isOpen == FALSE)) { 61 return (NILLNODE); 62 } 63 64 list->prevPtr = list->curPtr; 65 66 if (list->curPtr == NilListNode) { 67 if (list->atEnd == Unknown) { 68 /* 69 * If we're just starting out, atEnd will be Unknown. 70 * Then we want to start this thing off in the right 71 * direction -- at the start with atEnd being Middle. 72 */ 73 list->curPtr = tln = list->firstPtr; 74 list->atEnd = Middle; 75 } else { 76 tln = NilListNode; 77 list->atEnd = Tail; 78 } 79 } else { 80 tln = list->curPtr->nextPtr; 81 list->curPtr = tln; 82 83 if (tln == list->firstPtr || tln == NilListNode) { 84 /* 85 * If back at the front, then we've hit the end... 86 */ 87 list->atEnd = Tail; 88 } else { 89 /* 90 * Reset to Middle if gone past first. 91 */ 92 list->atEnd = Middle; 93 } 94 } 95 96 return ((LstNode)tln); 97 } 98 99