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      1 /*	$NetBSD: ftell.c,v 1.20 2012/03/27 15:05:42 christos 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. Neither the name of the University nor the names of its contributors
     19  *    may be used to endorse or promote products derived from this software
     20  *    without specific prior written permission.
     21  *
     22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     32  * SUCH DAMAGE.
     33  */
     34 
     35 #include <sys/cdefs.h>
     36 #if defined(LIBC_SCCS) && !defined(lint)
     37 #if 0
     38 static char sccsid[] = "@(#)ftell.c	8.2 (Berkeley) 5/4/95";
     39 #else
     40 __RCSID("$NetBSD: ftell.c,v 1.20 2012/03/27 15:05:42 christos Exp $");
     41 #endif
     42 #endif /* LIBC_SCCS and not lint */
     43 
     44 #include <assert.h>
     45 #include <errno.h>
     46 #include <stdio.h>
     47 #include "reentrant.h"
     48 #include "local.h"
     49 
     50 /*
     51  * ftell: return current offset.
     52  */
     53 long
     54 ftell(FILE *fp)
     55 {
     56 	off_t pos;
     57 
     58 
     59 	FLOCKFILE(fp);
     60 
     61 	if (fp->_seek == NULL) {
     62 		FUNLOCKFILE(fp);
     63 		errno = ESPIPE;			/* historic practice */
     64 		return -1L;
     65 	}
     66 
     67 	/*
     68 	 * Find offset of underlying I/O object, then
     69 	 * adjust for buffered bytes.
     70 	 */
     71 	(void)__sflush(fp); /* may adjust seek offset on append stream */
     72 	if (fp->_flags & __SOFF)
     73 		pos = fp->_offset;
     74 	else {
     75 		pos = (*fp->_seek)(fp->_cookie, (off_t)0, SEEK_CUR);
     76 		if (pos == -1L) {
     77 			FUNLOCKFILE(fp);
     78 			return (long)pos;
     79 		}
     80 	}
     81 	if (fp->_flags & __SRD) {
     82 		/*
     83 		 * Reading.  Any unread characters (including
     84 		 * those from ungetc) cause the position to be
     85 		 * smaller than that in the underlying object.
     86 		 */
     87 		pos -= fp->_r;
     88 		if (HASUB(fp))
     89 			pos -= fp->_ur;
     90 	} else if (fp->_flags & __SWR && fp->_p != NULL) {
     91 		/*
     92 		 * Writing.  Any buffered characters cause the
     93 		 * position to be greater than that in the
     94 		 * underlying object.
     95 		 */
     96 		pos += fp->_p - fp->_bf._base;
     97 	}
     98 	FUNLOCKFILE(fp);
     99 
    100 	if (__long_overflow(pos)) {
    101 		errno = EOVERFLOW;
    102 		return -1L;
    103 	}
    104 
    105 	return (long)pos;
    106 }
    107