77 lines
2.1 KiB
C
77 lines
2.1 KiB
C
/*-
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* LstPrev.c --
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* Get the node previous to the current one in the list and make it the
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* current node.
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* The sequential functions access the list in a slightly different way.
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* CurPtr points to their idea of the current node in the list and they
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* access the list based on it. Because the list is circular, Lst_Next
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* and Lst_Prev will go around the list forever. Lst_IsAtEnd must be
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* used to determine when to stop.
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*
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* Copyright (c) 1988 by University of California Regents
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*
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* Permission to use, copy, modify, and distribute this
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* software and its documentation for any purpose and without
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* fee is hereby granted, provided that the above copyright
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* notice appears in all copies. Neither the University of California nor
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* Adam de Boor makes any representations about the suitability of this
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* software for any purpose. It is provided "as is" without
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* express or implied warranty.
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*/
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#if !defined(lint) && defined(keep_rcsid)
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static char *rcsid =
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"Id: lstPrev.c,v 1.8 88/11/17 20:53:54 adam Exp $ SPRITE (Berkeley)";
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#endif lint
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#include "lstInt.h"
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/*-
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*-----------------------------------------------------------------------
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* Lst_Prev --
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* Return the node previous to the current one for the given list.
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*
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* Results:
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* The previous node or NILLNODE if the list hasn't been opened
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* yet or the beginning was reached.
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*
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* Side Effects:
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* the curPtr is changed to reflect reality.
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*
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*-----------------------------------------------------------------------
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*/
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LstNode
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Lst_Prev (l)
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Lst l;
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{
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register ListNode tln;
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register List list = (List)l;
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if ((LstValid (l) == FALSE) ||
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(list->isOpen == FALSE)) {
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return (NILLNODE);
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}
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list->prevPtr = list->curPtr;
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if (list->curPtr == NilListNode) {
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if (list->atEnd == Unknown) {
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list->curPtr = tln = list->lastPtr;
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list->atEnd = Middle;
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} else {
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tln = NilListNode;
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list->atEnd = Head;
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}
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} else {
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tln = list->curPtr->prevPtr;
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list->curPtr = tln;
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if (tln == list->lastPtr || tln == NilListNode) {
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list->atEnd = Head;
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} else {
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list->atEnd = Middle;
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}
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}
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return ((LstNode)tln);
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}
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