new file mode 100644
--- /dev/null
+++ b/lib/unlocked-io.h
@@ -0,0 +1,90 @@
+/* Prefer faster, non-thread-safe stdio functions if available.
+
+   Copyright (C) 2001, 2002 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify it
+   under the terms of the GNU Library General Public License as published
+   by the Free Software Foundation; either version 2, 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
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA.  */
+
+/* Written by Jim Meyering.  */
+
+#ifndef UNLOCKED_IO_H
+# define UNLOCKED_IO_H 1
+
+# ifndef USE_UNLOCKED_IO
+#  define USE_UNLOCKED_IO 1
+# endif
+
+# if USE_UNLOCKED_IO
+
+/* These are wrappers for functions/macros from GNU libc.
+   The standard I/O functions are thread-safe.  These *_unlocked ones are
+   more efficient but not thread-safe.  That they're not thread-safe is
+   fine since all of the applications in this package are single threaded.  */
+
+#  if HAVE_DECL_CLEARERR_UNLOCKED
+#   undef clearerr
+#   define clearerr(x) clearerr_unlocked (x)
+#  endif
+#  if HAVE_DECL_FEOF_UNLOCKED
+#   undef feof
+#   define feof(x) feof_unlocked (x)
+#  endif
+#  if HAVE_DECL_FERROR_UNLOCKED
+#   undef ferror
+#   define ferror(x) ferror_unlocked (x)
+#  endif
+#  if HAVE_DECL_FFLUSH_UNLOCKED
+#   undef fflush
+#   define fflush(x) fflush_unlocked (x)
+#  endif
+#  if HAVE_DECL_FGETS_UNLOCKED
+#   undef fgets
+#   define fgets(x,y,z) fgets_unlocked (x,y,z)
+#  endif
+#  if HAVE_DECL_FPUTC_UNLOCKED
+#   undef fputc
+#   define fputc(x,y) fputc_unlocked (x,y)
+#  endif
+#  if HAVE_DECL_FPUTS_UNLOCKED
+#   undef fputs
+#   define fputs(x,y) fputs_unlocked (x,y)
+#  endif
+#  if HAVE_DECL_FREAD_UNLOCKED
+#   undef fread
+#   define fread(w,x,y,z) fread_unlocked (w,x,y,z)
+#  endif
+#  if HAVE_DECL_FWRITE_UNLOCKED
+#   undef fwrite
+#   define fwrite(w,x,y,z) fwrite_unlocked (w,x,y,z)
+#  endif
+#  if HAVE_DECL_GETC_UNLOCKED
+#   undef getc
+#   define getc(x) getc_unlocked (x)
+#  endif
+#  if HAVE_DECL_GETCHAR_UNLOCKED
+#   undef getchar
+#   define getchar() getchar_unlocked ()
+#  endif
+#  if HAVE_DECL_PUTC_UNLOCKED
+#   undef putc
+#   define putc(x,y) putc_unlocked (x,y)
+#  endif
+#  if HAVE_DECL_PUTCHAR_UNLOCKED
+#   undef putchar
+#   define putchar(x) putchar_unlocked (x)
+#  endif
+
+# endif /* USE_UNLOCKED_IO */
+#endif /* UNLOCKED_IO_H */