lib/freadahead.c

   1 /* Retrieve information about a FILE stream.
   2    Copyright (C) 2007-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include "freadahead.h"
  21
  22 #include <stdlib.h>
  23 #include "stdio-impl.h"
  24
  25 #if defined __DragonFly__
  26 /* Defined in libc, but not declared in <stdio.h>.  */
  27 extern size_t __sreadahead (FILE *);
  28 #endif
  29
  30 /* This file is not used on systems that have the __freadahead function,
  31    namely musl libc.  */
  32
  33 size_t
  34 freadahead (FILE *fp)
  35 {
  36 #if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
  37   /* GNU libc, BeOS, Haiku, Linux libc5 */
  38   if (fp->_IO_write_ptr > fp->_IO_write_base)
  39     return 0;
  40   return (fp->_IO_read_end - fp->_IO_read_ptr)
  41          + (fp->_flags & _IO_IN_BACKUP ? fp->_IO_save_end - fp->_IO_save_base :
  42             0);
  43 #elif defined __sferror || defined __DragonFly__ || defined __ANDROID__
  44   /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
  45   if ((fp_->_flags & __SWR) != 0 || fp_->_r < 0)
  46     return 0;
  47 # if defined __DragonFly__
  48   return __sreadahead (fp);
  49 # else
  50   return fp_->_r
  51          + (HASUB (fp) ? fp_->_ur : 0);
  52 # endif
  53 #elif defined __EMX__               /* emx+gcc */
  54   if ((fp->_flags & _IOWRT) != 0)
  55     return 0;
  56   /* Note: fp->_ungetc_count > 0 implies fp->_rcount <= 0,
  57            fp->_ungetc_count = 0 implies fp->_rcount >= 0.  */
  58   /* equivalent to
  59      (fp->_ungetc_count == 0 ? fp->_rcount : fp->_ungetc_count - fp->_rcount) */
  60   return (fp->_rcount > 0 ? fp->_rcount : fp->_ungetc_count - fp->_rcount);
  61 #elif defined __minix               /* Minix */
  62   if ((fp_->_flags & _IOWRITING) != 0)
  63     return 0;
  64   return fp_->_count;
  65 #elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, UnixWare, mingw, MSVC, NonStop Kernel, OpenVMS */
  66   if ((fp_->_flag & _IOWRT) != 0)
  67     return 0;
  68   return fp_->_cnt;
  69 #elif defined __UCLIBC__            /* uClibc */
  70 # ifdef __STDIO_BUFFERS
  71   if (fp->__modeflags & __FLAG_WRITING)
  72     return 0;
  73   return (fp->__bufread - fp->__bufpos)
  74          + (fp->__modeflags & __FLAG_UNGOT ? 1 : 0);
  75 # else
  76   return 0;
  77 # endif
  78 #elif defined __QNX__               /* QNX */
  79   if ((fp->_Mode & 0x2000 /* _MWRITE */) != 0)
  80     return 0;
  81   /* fp->_Buf <= fp->_Next <= fp->_Rend,
  82      and fp->_Rend may be overridden by fp->_Rsave. */
  83   return ((fp->_Rsave ? fp->_Rsave : fp->_Rend) - fp->_Next)
  84          + (fp->_Mode & 0x4000 /* _MBYTE */
  85             ? (fp->_Back + sizeof (fp->_Back)) - fp->_Rback
  86             : 0);
  87 #elif defined __MINT__              /* Atari FreeMiNT */
  88   if (!fp->__mode.__read)
  89     return 0;
  90   return (fp->__pushed_back
  91           ? fp->__get_limit - fp->__pushback_bufp + 1
  92           : fp->__get_limit - fp->__bufp);
  93 #elif defined EPLAN9                /* Plan9 */
  94   if (fp->state == 4 /* WR */ || fp->rp >= fp->wp)
  95     return 0;
  96   return fp->wp - fp->rp;
  97 #elif defined SLOW_BUT_NO_HACKS     /* users can define this */
  98   abort ();
  99   return 0;
 100 #else
 101  #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."
 102 #endif
 103 }