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ftell.c revision 1.4 
      1 /*	$NetBSD: ftell.c,v 1.4 1995/02/02 02:09:42 jtc Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1990, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * Chris Torek.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *	This product includes software developed by the University of
     21  *	California, Berkeley and its contributors.
     22  * 4. Neither the name of the University nor the names of its contributors
     23  *    may be used to endorse or promote products derived from this software
     24  *    without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     36  * SUCH DAMAGE.
     37  */
     38 
     39 #if defined(LIBC_SCCS) && !defined(lint)
     40 #if 0
     41 static char sccsid[] = "@(#)ftell.c	8.1 (Berkeley) 6/4/93";
     42 #endif
     43 static char rcsid[] = "$NetBSD: ftell.c,v 1.4 1995/02/02 02:09:42 jtc Exp $";
     44 #endif /* LIBC_SCCS and not lint */
     45 
     46 #include <stdio.h>
     47 #include <errno.h>
     48 #include "local.h"
     49 
     50 /*
     51  * ftell: return current offset.
     52  */
     53 long
     54 ftell(fp)
     55 	register const FILE *fp;
     56 {
     57 	register fpos_t pos;
     58 
     59 	if (fp->_seek == NULL) {
     60 		errno = ESPIPE;			/* historic practice */
     61 		return (-1L);
     62 	}
     63 
     64 	/*
     65 	 * Find offset of underlying I/O object, then
     66 	 * adjust for buffered bytes.
     67 	 */
     68 	if (fp->_flags & __SOFF)
     69 		pos = fp->_offset;
     70 	else {
     71 		pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
     72 		if (pos == -1L)
     73 			return (pos);
     74 	}
     75 	if (fp->_flags & __SRD) {
     76 		/*
     77 		 * Reading.  Any unread characters (including
     78 		 * those from ungetc) cause the position to be
     79 		 * smaller than that in the underlying object.
     80 		 */
     81 		pos -= fp->_r;
     82 		if (HASUB(fp))
     83 			pos -= fp->_ur;
     84 	} else if (fp->_flags & __SWR && fp->_p != NULL) {
     85 		/*
     86 		 * Writing.  Any buffered characters cause the
     87 		 * position to be greater than that in the
     88 		 * underlying object.
     89 		 */
     90 		pos += fp->_p - fp->_bf._base;
     91 	}
     92 	return (pos);
     93 }
     94