1/*	$NetBSD: ftell.c,v 1.19 2012/03/15 18:22:30 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
38static char sccsid[] = "@(#)ftell.c	8.2 (Berkeley) 5/4/95";
39#else
40__RCSID("$NetBSD: ftell.c,v 1.19 2012/03/15 18:22:30 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 */
53long
54ftell(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