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[] = "@(#)lstPrev.c 5.2 (Berkeley) 03/11/90"; 23 #endif /* not lint */ 24 25 /*- 26 * LstPrev.c -- 27 * Get the node previous to the current one in the list and make it the 28 * current node. 29 * The sequential functions access the list in a slightly different way. 30 * CurPtr points to their idea of the current node in the list and they 31 * access the list based on it. Because the list is circular, Lst_Next 32 * and Lst_Prev will go around the list forever. Lst_IsAtEnd must be 33 * used to determine when to stop. 34 */ 35 36 #include "lstInt.h" 37 38 /*- 39 *----------------------------------------------------------------------- 40 * Lst_Prev -- 41 * Return the node previous to the current one for the given list. 42 * 43 * Results: 44 * The previous node or NILLNODE if the list hasn't been opened 45 * yet or the beginning was reached. 46 * 47 * Side Effects: 48 * the curPtr is changed to reflect reality. 49 * 50 *----------------------------------------------------------------------- 51 */ 52 LstNode 53 Lst_Prev (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 list->curPtr = tln = list->lastPtr; 69 list->atEnd = Middle; 70 } else { 71 tln = NilListNode; 72 list->atEnd = Head; 73 } 74 } else { 75 tln = list->curPtr->prevPtr; 76 list->curPtr = tln; 77 if (tln == list->lastPtr || tln == NilListNode) { 78 list->atEnd = Head; 79 } else { 80 list->atEnd = Middle; 81 } 82 } 83 84 return ((LstNode)tln); 85 } 86 87