new file mode 100644
--- /dev/null
+++ b/lib/addext.c
@@ -0,0 +1,106 @@
+/* addext.c -- add an extension to a file name
+   Copyright (C) 1990, 1997 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 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING.
+   If not, write to the Free Software Foundation,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+/* Written by David MacKenzie <djm@gnu.ai.mit.edu> and Paul Eggert */
+
+#if HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#ifndef HAVE_DOS_FILE_NAMES
+#define HAVE_DOS_FILE_NAMES 0
+#endif
+#ifndef HAVE_LONG_FILE_NAMES
+#define HAVE_LONG_FILE_NAMES 0
+#endif
+
+#include <backupfile.h>
+
+#if HAVE_LIMITS_H
+# include <limits.h>
+#endif
+#ifndef _POSIX_NAME_MAX
+#define _POSIX_NAME_MAX 14
+#endif
+
+#include <sys/types.h>
+#if HAVE_STRING_H
+# include <string.h>
+#else
+# include <strings.h>
+#endif
+
+#if HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
+/* Append to FILENAME the extension EXT, unless the result would be too long,
+   in which case just append the character E.  */
+
+void
+addext (filename, ext, e)
+     char *filename;
+     char const *ext;
+     int e;
+{
+  char *s = base_name (filename);
+  size_t slen = strlen (s), extlen = strlen (ext);
+  long slen_max = -1;
+
+#if HAVE_PATHCONF && defined _PC_NAME_MAX
+  if (slen + extlen <= _POSIX_NAME_MAX && ! HAVE_DOS_FILE_NAMES)
+    /* The file name is so short there's no need to call pathconf.  */
+    slen_max = _POSIX_NAME_MAX;
+  else if (s == filename)
+    slen_max = pathconf (".", _PC_NAME_MAX);
+  else
+    {
+      char c = *s;
+      *s = 0;
+      slen_max = pathconf (filename, _PC_NAME_MAX);
+      *s = c;
+    }
+#endif
+  if (slen_max < 0)
+    slen_max = HAVE_LONG_FILE_NAMES ? 255 : 14;
+
+  if (HAVE_DOS_FILE_NAMES && slen_max <= 12)
+    {
+      /* Live within DOS's 8.3 limit.  */
+      char *dot = strchr (s, '.');
+      if (dot)
+	{
+	  slen -= dot + 1 - s;
+	  s = dot + 1;
+	  slen_max = 3;
+	}
+      else
+	slen_max = 8;
+      extlen = 9; /* Don't use EXT.  */
+    }
+
+  if (slen + extlen <= slen_max)
+    strcpy (s + slen, ext);
+  else
+    {
+      if (slen_max <= slen)
+	slen = slen_max - 1;
+      s[slen] = e;
+      s[slen + 1] = 0;
+    }
+}