glue-fseek.c

/*
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

/*
FUNCTION
<<fseek>>, <<fseeko>>---set file position

INDEX
        fseek
INDEX
        fseeko
INDEX
        _fseek_r
INDEX
        _fseeko_r

ANSI_SYNOPSIS
        #include <stdio.h>
        int fseek(FILE *<[fp]>, long <[offset]>, int <[whence]>)
        int fseeko(FILE *<[fp]>, off_t <[offset]>, int <[whence]>)
        int _fseek_r(struct _reent *<[ptr]>, FILE *<[fp]>,
                     long <[offset]>, int <[whence]>)
        int _fseeko_r(struct _reent *<[ptr]>, FILE *<[fp]>,
                     off_t <[offset]>, int <[whence]>)

TRAD_SYNOPSIS
        #include <stdio.h>
        int fseek(<[fp]>, <[offset]>, <[whence]>)
        FILE *<[fp]>;
        long <[offset]>;
        int <[whence]>;

        int fseeko(<[fp]>, <[offset]>, <[whence]>)
        FILE *<[fp]>;
        off_t <[offset]>;
        int <[whence]>;

        int _fseek_r(<[ptr]>, <[fp]>, <[offset]>, <[whence]>)
        struct _reent *<[ptr]>;
        FILE *<[fp]>;
        long <[offset]>;
        int <[whence]>;

        int _fseeko_r(<[ptr]>, <[fp]>, <[offset]>, <[whence]>)
        struct _reent *<[ptr]>;
        FILE *<[fp]>;
        off_t <[offset]>;
        int <[whence]>;

DESCRIPTION
Objects of type <<FILE>> can have a ``position'' that records how much
of the file your program has already read.  Many of the <<stdio>> functions
depend on this position, and many change it as a side effect.

You can use <<fseek>>/<<fseeko>> to set the position for the file identified by
<[fp]>.  The value of <[offset]> determines the new position, in one
of three ways selected by the value of <[whence]> (defined as macros
in `<<stdio.h>>'):

<<SEEK_SET>>---<[offset]> is the absolute file position (an offset
from the beginning of the file) desired.  <[offset]> must be positive.

<<SEEK_CUR>>---<[offset]> is relative to the current file position.
<[offset]> can meaningfully be either positive or negative.

<<SEEK_END>>---<[offset]> is relative to the current end of file.
<[offset]> can meaningfully be either positive (to increase the size
of the file) or negative.

See <<ftell>>/<<ftello>> to determine the current file position.

RETURNS
<<fseek>>/<<fseeko>> return <<0>> when successful.  On failure, the
result is <<EOF>>.  The reason for failure is indicated in <<errno>>:
either <<ESPIPE>> (the stream identified by <[fp]> doesn't support
repositioning) or <<EINVAL>> (invalid file position).

PORTABILITY
ANSI C requires <<fseek>>.

<<fseeko>> is defined by the Single Unix specification.

Supporting OS subroutines required: <<close>>, <<fstat>>, <<isatty>>,
<<lseek>>, <<read>>, <<sbrk>>, <<write>>.
*/

#define _COMPILING_NEWLIB

#include "newlib.h"

#include <stdio.h>

#include "local.h"
#include <_ansi.h>
#include <errno.h>
#include <fcntl.h>
#include <reent.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <time.h>

#define POS_ERR (-(_fpos_t) 1)

/*
 * Seek the given file to the given offset.
 * `Whence' must be one of the three SEEK_* macros.
 */

typedef _fpos_t _EXFUN((*seek_fnptr), (struct _reent *, _PTR, _fpos_t, int) );

int _fseek_r(struct _reent *ptr, register FILE *fp, long offset, int whence)
{
    _fpos_t _EXFUN((*seekfn), (struct _reent *, _PTR, _fpos_t, int) );
    _fpos_t target;
    _fpos_t curoff = 0;
    size_t n;
#ifdef __USE_INTERNAL_STAT64
    struct stat64 st;
#else
    struct stat st;
#endif
    int havepos;

    /* Make sure stdio is set up.  */

    CHECK_INIT(ptr, fp);

    _flockfile(fp);

    /* If we've been doing some writing, and we're in append mode
       then we don't really know where the filepos is.  */

    if (fp->_flags & __SAPP && fp->_flags & __SWR)
    {
        /* So flush the buffer and seek to the end.  */
        _fflush_r(ptr, fp);
    }

    /* Have to be able to seek.  */

    if ((seekfn = (seek_fnptr) fp->_seek) == NULL)
    {
        ptr->_errno = ESPIPE; /* ??? */
        _funlockfile(fp);
        return EOF;
    }

    if (_fflush_r(ptr, fp) ||
        seekfn(ptr, fp->_cookie, offset, whence) == POS_ERR)
    {
        _funlockfile(fp);
        return EOF;
    }
    /* success: clear EOF indicator and discard ungetc() data */
    if (HASUB(fp))
        FREEUB(ptr, fp);
    fp->_p = fp->_bf._base;
    fp->_r = 0;
    /* fp->_w = 0; */ /* unnecessary (I think...) */
    fp->_flags &= ~__SEOF;
    /* Reset no-optimization flag after successful seek.  The
       no-optimization flag may be set in the case of a read
       stream that is flushed which by POSIX/SUSv3 standards,
       means that a corresponding seek must not optimize.  The
       optimization is then allowed if no subsequent flush
       is performed.  */
    fp->_flags &= ~__SNPT;
    // memset (&fp->_mbstate, 0, sizeof (_mbstate_t));
    _funlockfile(fp);
    return 0;
}

#ifndef _REENT_ONLY

int fseek(register FILE *fp, long offset, int whence)
{
    return _fseek_r(_REENT, fp, offset, whence);
}

#endif /* !_REENT_ONLY */