/*      $OpenBSD: ftell.c,v 1.14 2025/06/03 14:15:53 yasuoka Exp $ */
/*-
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <stdio.h>
#include <errno.h>
#include <limits.h>
#include "local.h"

/*
 * ftello: return current offset.
 */
off_t
ftello(FILE *fp)
{
        fpos_t pos;

        if (fp->_seek == NULL) {
                errno = ESPIPE;                 /* historic practice */
                pos = -1;
                goto out;
        }

        /*
         * Find offset of underlying I/O object, then
         * adjust for buffered bytes.
         */
        FLOCKFILE(fp);
        if (fp->_flags & __SWR)
                __sflush(fp);   /* may adjust seek offset on append stream */
        if (fp->_flags & __SOFF)
                pos = fp->_offset;
        else {
                pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
                if (pos == -1)
                        goto out;
        }
        if (fp->_flags & __SRD) {
                /*
                 * Reading.  Any unread characters (including
                 * those from ungetc) cause the position to be
                 * smaller than that in the underlying object.
                 */
                pos -= fp->_r;
                if (HASUB(fp))
                        pos -= fp->_ur;
        } else if (fp->_flags & __SWR && fp->_p != NULL) {
                /*
                 * Writing.  Any buffered characters cause the
                 * position to be greater than that in the
                 * underlying object.
                 */
                pos += fp->_p - fp->_bf._base;
        }
out:    FUNLOCKFILE(fp);
        return (pos);
}
DEF_WEAK(ftello);

long
ftell(FILE *fp)
{
        off_t offset = ftello(fp);
        if (offset > LONG_MAX) {
                errno = EOVERFLOW;
                return (-1);
        }
        return ((long)offset);
}
DEF_STRONG(ftell);