##### http://autoconf-archive.cryp.to/ac_define_sub_path.html
#
# SYNOPSIS
#
#   AC_DEFINE_SUB_PATH(DEFNAME, varname, description)
#
# DESCRIPTION
#
#   Look at varname and detect the subpath that it contains relative to
#   $prefix/$exec_prefix. If the path is indeed relative to
#   $prefix/$exec_prefix, then a single "./" (dotslash) is prepended,
#   otherwise it can be seen as an absolute path that can not be moved,
#   which you possibly do for "/etc" files, or even those ending up in
#   "/lib/modules" or "/winnt/system".
#
#   This macro is not very intelligent, it's just a first try in this
#   direction. It does currently just look into the current patterns,
#   and replaces a ${prefix} with a simple dot. Amazingly, it works
#   quite well for most packages.
#
#   Example (configure.ac):
#
#      AC_DEFINE_DIR([EPREFIX], [exec_prefix], [--exec-prefix or default])
#      AC_DEFINE_SUB_PATH([PATH_LIBDIR], [libdir], [--bindir subdir])
#      AC_DEFINE_UNQUOTED([PACKAGE],"$PACKAGE", [Name of package])
#
#   Example (in C):
#
#      static const char _libdir[] = PATH_LIBDIR; /* configure default */
#      char* libdir;
#      char* eprefix = getenv (PACKAGE "DIR");
#      if (! eprefix) eprefix = EPREFIX; /* default */
#      if (*_libdir != '.') libdir = strdup(_libdir);
#      else {
#         libdir = malloc(strlen(eprefix) + strlen(_libdir) + 2);
#         strcpy(libdir, eprefix);
#         strcat(libdir, PATH_DELIMITER_STRING);
#         strcat(libdir, _libdir);
#      }
#      ...
#      free (libdir);
#
#   The AC_DEFINE_SUB_PATHS(varnames) macro looks for the given various
#   install-paths that largely depend on either ${prefix} or
#   ${exec_prefix}. Just cut out the prefix and ac_define the value.
#   The value is uppercased and PATH_ prepended ie.
#   ac_define_sub_paths(bindir libdir pkgdatadir) will create the
#   defines PATH_BINDIR PATH_LIBDIR PATH_PKGDATADIR - see posix'
#   include/paths.h that creates _PATH_DEV and friends.
#
# LAST MODIFICATION
#
#   2006-10-13
#
# COPYLEFT
#
#   Copyright (c) 2006 Guido U. Draheim <guidod@gmx.de>
#
#   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 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, write to the Free Software
#   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
#   02111-1307, USA.
#
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#   may extend this special exception to the GPL to apply to your
#   modified version as well.

AC_DEFUN([AC_DEFINE_SUB_PATH],
[dnl
  test "_$prefix" = _NONE && prefix="$ac_default_prefix"
  test "_$exec_prefix" = _NONE && exec_prefix='${prefix}'
  P=`echo ifelse( $2, , [$]$1, [$]$2) | sed -e 's:^\${[a-z_]*prefix}:.:'`
  ifelse ($3, ,
    AC_DEFINE($1, $P, [sub path $2]),
    AC_DEFINE($1, $P, $3))
])

AC_DEFUN([AC_DEFINE_SUB_PATHS],
[dnl
  test "_$prefix" = _NONE && prefix="$ac_default_prefix"
  test "_$exec_prefix" = _NONE && exec_prefix='${prefix}'
  for i in $1 ; do
  P=`echo \$$i | sed -e 's:^\${[a-z_]*prefix}:.:'`
  V=`echo path_$i | sed -e 'y:abcdefghijklmnopqrstuvwxyz:ABCDEFGHIJKLMNOPQRSTUVWXYZ:'`
    AC_DEFINE($V, $P, [sub path $i]),
])