new file mode 100644
--- /dev/null
+++ b/lib/stdio-impl.h
@@ -0,0 +1,67 @@
+/* Implementation details of FILE streams.
+   Copyright (C) 2007-2008 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 <http://www.gnu.org/licenses/>.  */
+
+/* Many stdio implementations have the same logic and therefore can share
+   the same implementation of stdio extension API, except that some fields
+   have different naming conventions, or their access requires some casts.  */
+
+
+/* BSD stdio derived implementations.  */
+
+#if defined __sferror               /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
+
+# if defined __NetBSD__ || defined __OpenBSD__ /* NetBSD, OpenBSD */
+  /* See <http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/stdio/fileext.h?rev=HEAD&content-type=text/x-cvsweb-markup>
+     and <http://www.openbsd.org/cgi-bin/cvsweb/src/lib/libc/stdio/fileext.h?rev=HEAD&content-type=text/x-cvsweb-markup> */
+  struct __sfileext
+    {
+      struct  __sbuf _ub; /* ungetc buffer */
+      /* More fields, not relevant here.  */
+    };
+#  define fp_ub ((struct __sfileext *) fp->_ext._base)->_ub
+# else                                         /* FreeBSD, MacOS X, Cygwin */
+#  define fp_ub fp->_ub
+# endif
+
+# define HASUB(fp) (fp_ub._base != NULL)
+
+#endif
+
+
+/* SystemV derived implementations.  */
+
+#if defined _IOERR
+
+# if defined __sun && defined _LP64 /* Solaris/{SPARC,AMD64} 64-bit */
+#  define fp_ ((struct { unsigned char *_ptr; \
+			 unsigned char *_base; \
+			 unsigned char *_end; \
+			 long _cnt; \
+			 int _file; \
+			 unsigned int _flag; \
+		       } *) fp)
+# else
+#  define fp_ fp
+# endif
+
+# if defined _SCO_DS                /* OpenServer */
+#  define _cnt __cnt
+#  define _ptr __ptr
+#  define _base __base
+#  define _flag __flag
+# endif
+
+#endif