1*40411Sbostic /*- 2*40411Sbostic * LstPrev.c -- 3*40411Sbostic * Get the node previous to the current one in the list and make it the 4*40411Sbostic * current node. 5*40411Sbostic * The sequential functions access the list in a slightly different way. 6*40411Sbostic * CurPtr points to their idea of the current node in the list and they 7*40411Sbostic * access the list based on it. Because the list is circular, Lst_Next 8*40411Sbostic * and Lst_Prev will go around the list forever. Lst_IsAtEnd must be 9*40411Sbostic * used to determine when to stop. 10*40411Sbostic * 11*40411Sbostic * Copyright (c) 1988 by University of California Regents 12*40411Sbostic * 13*40411Sbostic * Permission to use, copy, modify, and distribute this 14*40411Sbostic * software and its documentation for any purpose and without 15*40411Sbostic * fee is hereby granted, provided that the above copyright 16*40411Sbostic * notice appears in all copies. Neither the University of California nor 17*40411Sbostic * Adam de Boor makes any representations about the suitability of this 18*40411Sbostic * software for any purpose. It is provided "as is" without 19*40411Sbostic * express or implied warranty. 20*40411Sbostic */ 21*40411Sbostic #ifndef lint 22*40411Sbostic static char *rcsid = 23*40411Sbostic "$Id: lstPrev.c,v 1.8 88/11/17 20:53:54 adam Exp $ SPRITE (Berkeley)"; 24*40411Sbostic #endif lint 25*40411Sbostic 26*40411Sbostic #include "lstInt.h" 27*40411Sbostic 28*40411Sbostic /*- 29*40411Sbostic *----------------------------------------------------------------------- 30*40411Sbostic * Lst_Prev -- 31*40411Sbostic * Return the node previous to the current one for the given list. 32*40411Sbostic * 33*40411Sbostic * Results: 34*40411Sbostic * The previous node or NILLNODE if the list hasn't been opened 35*40411Sbostic * yet or the beginning was reached. 36*40411Sbostic * 37*40411Sbostic * Side Effects: 38*40411Sbostic * the curPtr is changed to reflect reality. 39*40411Sbostic * 40*40411Sbostic *----------------------------------------------------------------------- 41*40411Sbostic */ 42*40411Sbostic LstNode 43*40411Sbostic Lst_Prev (l) 44*40411Sbostic Lst l; 45*40411Sbostic { 46*40411Sbostic register ListNode tln; 47*40411Sbostic register List list = (List)l; 48*40411Sbostic 49*40411Sbostic if ((LstValid (l) == FALSE) || 50*40411Sbostic (list->isOpen == FALSE)) { 51*40411Sbostic return (NILLNODE); 52*40411Sbostic } 53*40411Sbostic 54*40411Sbostic list->prevPtr = list->curPtr; 55*40411Sbostic 56*40411Sbostic if (list->curPtr == NilListNode) { 57*40411Sbostic if (list->atEnd == Unknown) { 58*40411Sbostic list->curPtr = tln = list->lastPtr; 59*40411Sbostic list->atEnd = Middle; 60*40411Sbostic } else { 61*40411Sbostic tln = NilListNode; 62*40411Sbostic list->atEnd = Head; 63*40411Sbostic } 64*40411Sbostic } else { 65*40411Sbostic tln = list->curPtr->prevPtr; 66*40411Sbostic list->curPtr = tln; 67*40411Sbostic if (tln == list->lastPtr || tln == NilListNode) { 68*40411Sbostic list->atEnd = Head; 69*40411Sbostic } else { 70*40411Sbostic list->atEnd = Middle; 71*40411Sbostic } 72*40411Sbostic } 73*40411Sbostic 74*40411Sbostic return ((LstNode)tln); 75*40411Sbostic } 76*40411Sbostic 77