#ifndef lintstatic char	*sccsid = " @(#)backspace.c	1.2	(ULTRIX)	1/16/86";#endif lint/************************************************************************ *									* *			Copyright (c) 1986 by				* *		Digital Equipment Corporation, Maynard, MA		* *			All rights reserved.				* *									* *   This software is furnished under a license and may be used and	* *   copied  only  in accordance with the terms of such license and	* *   with the  inclusion  of  the  above  copyright  notice.   This	* *   software  or  any  other copies thereof may not be provided or	* *   otherwise made available to any other person.  No title to and	* *   ownership of the software is hereby transferred.			* *									* *   This software is  derived  from  software  received  from  the	* *   University    of   California,   Berkeley,   and   from   Bell	* *   Laboratories.  Use, duplication, or disclosure is  subject  to	* *   restrictions  under  license  agreements  with  University  of	* *   California and with AT&T.						* *									* *   The information in this software is subject to change  without	* *   notice  and should not be construed as a commitment by Digital	* *   Equipment Corporation.						* *									* *   Digital assumes no responsibility for the use  or  reliability	* *   of its software on equipment which is not supplied by Digital.	* *									* ************************************************************************//**************************************************************************			Modification History**	David Metsky		10-Jan-86** 001	Replaced old version with BSD 4.3 version as part of upgrade.**	Based on:	backspace.c	5.2		7/30/85**************************************************************************//* * Backspace records */#include "fio.h"static char	bksp[]	= "backspace";char	last_char();f_back(a)alist	*a;{	unit *b;	int n,i;	long x,y;	lfname = NULL;	elist = NO;	external = YES;	errflag = a->aerr;	lunit = a->aunit;	if (not_legal(lunit))		err(errflag, F_ERUNIT, bksp)	b= &units[lunit];	if(!b->ufd) return(OK);	lfname = b->ufnm;	if(b->uend)	{	b->uend = NO;		clearerr(b->ufd);		return(OK);	}	if((x = ftell(b->ufd)) == 0)		return(OK);	if(!b->useek)		err(errflag, F_ERNOBKSP, bksp)	if(b->uwrt && (n = t_runc(b, errflag, bksp)))	/* sets 'reading' */		return(n);	if(b->url)		/* direct access, purely academic */	{	y = x%(long)b->url;		x -= y?y:b->url;		fseek(b->ufd,x,0);		return(OK);	}	if(!b->ufmt)		/* unformatted sequential */	{	fseek(b->ufd,-(long)sizeof(int),1);		fread((char *)&n,sizeof(int),1,b->ufd);		fseek(b->ufd,-(long)n-2*sizeof(int),1);		return(OK);	}	if(x == 1)			/* formatted sequential */	{	rewind(b->ufd);		return(OK);	}	while (last_char(b->ufd) != '\n')	/* slow but simple */		;	return(OK);}