1 /*- 2 * LstNext.c -- 3 * Return the next node for a list. 4 * The sequential functions access the list in a slightly different way. 5 * CurPtr points to their idea of the current node in the list and they 6 * access the list based on it. Because the list is circular, Lst_Next 7 * and Lst_Prev will go around the list forever. Lst_IsAtEnd must be 8 * used to determine when to stop. 9 * 10 * Copyright (c) 1988 by University of California Regents 11 * 12 * Permission to use, copy, modify, and distribute this 13 * software and its documentation for any purpose and without 14 * fee is hereby granted, provided that the above copyright 15 * notice appears in all copies. Neither the University of California nor 16 * Adam de Boor makes any representations about the suitability of this 17 * software for any purpose. It is provided "as is" without 18 * express or implied warranty. 19 */ 20 #ifndef lint 21 static char *rcsid = 22 "$Id: lstNext.c,v 1.8 88/11/17 20:53:40 adam Exp $ SPRITE (Berkeley)"; 23 #endif lint 24 25 #include "lstInt.h" 26 27 /*- 28 *----------------------------------------------------------------------- 29 * Lst_Next -- 30 * Return the next node for the given list. 31 * 32 * Results: 33 * The next node or NILLNODE if the list has yet to be opened. Also 34 * if the list is non-circular and the end has been reached, NILLNODE 35 * is returned. 36 * 37 * Side Effects: 38 * the curPtr field is updated. 39 * 40 *----------------------------------------------------------------------- 41 */ 42 LstNode 43 Lst_Next (l) 44 Lst l; 45 { 46 register ListNode tln; 47 register List list = (List)l; 48 49 if ((LstValid (l) == FALSE) || 50 (list->isOpen == FALSE)) { 51 return (NILLNODE); 52 } 53 54 list->prevPtr = list->curPtr; 55 56 if (list->curPtr == NilListNode) { 57 if (list->atEnd == Unknown) { 58 /* 59 * If we're just starting out, atEnd will be Unknown. 60 * Then we want to start this thing off in the right 61 * direction -- at the start with atEnd being Middle. 62 */ 63 list->curPtr = tln = list->firstPtr; 64 list->atEnd = Middle; 65 } else { 66 tln = NilListNode; 67 list->atEnd = Tail; 68 } 69 } else { 70 tln = list->curPtr->nextPtr; 71 list->curPtr = tln; 72 73 if (tln == list->firstPtr || tln == NilListNode) { 74 /* 75 * If back at the front, then we've hit the end... 76 */ 77 list->atEnd = Tail; 78 } else { 79 /* 80 * Reset to Middle if gone past first. 81 */ 82 list->atEnd = Middle; 83 } 84 } 85 86 return ((LstNode)tln); 87 } 88 89