/* Retrieve information about a FILE stream.

   Copyright (C) 2007-2018 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */

#include "freadahead.h"

#include <stdlib.h>

#include "stdio-impl.h"

#if defined __DragonFly__

/* Defined in libc, but not declared in <stdio.h>.  */

extern size_t __sreadahead (FILE *);

#endif

/* This file is not used on systems that have the __freadahead function,

   namely musl libc.  */

size_t

freadahead (FILE *fp)

{

#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1

  /* GNU libc, BeOS, Haiku, Linux libc5 */

  if (fp->_IO_write_ptr > fp->_IO_write_base)

    return 0;

  return (fp->_IO_read_end - fp->_IO_read_ptr)

         + (fp->_flags & _IO_IN_BACKUP ? fp->_IO_save_end - fp->_IO_save_base :

            0);

#elif defined __sferror || defined __DragonFly__ || defined __ANDROID__

  /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */

  if ((fp_->_flags & __SWR) != 0 || fp_->_r < 0)

    return 0;

# if defined __DragonFly__

  return __sreadahead (fp);

# else

  return fp_->_r

         + (HASUB (fp) ? fp_->_ur : 0);

# endif

#elif defined __EMX__               /* emx+gcc */

  if ((fp->_flags & _IOWRT) != 0)

    return 0;

  /* Note: fp->_ungetc_count > 0 implies fp->_rcount <= 0,

           fp->_ungetc_count = 0 implies fp->_rcount >= 0.  */

  /* equivalent to

     (fp->_ungetc_count == 0 ? fp->_rcount : fp->_ungetc_count - fp->_rcount) */

  return (fp->_rcount > 0 ? fp->_rcount : fp->_ungetc_count - fp->_rcount);

#elif defined __minix               /* Minix */

  if ((fp_->_flags & _IOWRITING) != 0)

    return 0;

  return fp_->_count;

#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, MSVC, NonStop Kernel, OpenVMS */

  if ((fp_->_flag & _IOWRT) != 0)

    return 0;

  return fp_->_cnt;

#elif defined __UCLIBC__            /* uClibc */

# ifdef __STDIO_BUFFERS

  if (fp->__modeflags & __FLAG_WRITING)

    return 0;

  return (fp->__bufread - fp->__bufpos)

         + (fp->__modeflags & __FLAG_UNGOT ? 1 : 0);

# else

  return 0;

# endif

#elif defined __QNX__               /* QNX */

  if ((fp->_Mode & 0x2000 /* _MWRITE */) != 0)

    return 0;

  /* fp->_Buf <= fp->_Next <= fp->_Rend,

     and fp->_Rend may be overridden by fp->_Rsave. */

  return ((fp->_Rsave ? fp->_Rsave : fp->_Rend) - fp->_Next)

         + (fp->_Mode & 0x4000 /* _MBYTE */

            ? (fp->_Back + sizeof (fp->_Back)) - fp->_Rback

            : 0);

#elif defined __MINT__              /* Atari FreeMiNT */

  if (!fp->__mode.__read)

    return 0;

  return (fp->__pushed_back

          ? fp->__get_limit - fp->__pushback_bufp + 1

          : fp->__get_limit - fp->__bufp);

#elif defined EPLAN9                /* Plan9 */

  if (fp->state == 4 /* WR */ || fp->rp >= fp->wp)

    return 0;

  return fp->wp - fp->rp;

#elif defined SLOW_BUT_NO_HACKS     /* users can define this */

  abort ();

  return 0;

#else

 #error "Please port gnulib freadahead.c to your platform! Look at the definition of fflush, fread, ungetc on your system, then report this to bug-gnulib."

#endif

}