Thanks to TU-Berlin's Polymake Team, cdd+ now runs with GNU's GMP rational library as well as with the GNU g++ Rational library. In particular, Polymake Team (Ewgenij Gawrilow and Michael Joswig) wrote C++ wrappers "gmp_integer.cc" and "gmp_rational.cc" for GMP which cdd+ can now use instead of GNU's G++ Rational arithmetic library.
Since cdd+ with GMP runs substantially faster than cddr+ with g++Rational, any cdd+ user who needs exact arithmetic computation is strongly recommended to use the GMP version. One should be also aware that GMP-2.0.2 has known bugs and all the patches available from GMP-Homepage (http://www.matematik.su.se/~tege/gmp/) should be applied first. Even with all these troubles, its speed compensates them easily. How much faster? It all depends on your data. For kkd* polytopes included in cdd+, cddr+_gmp runs three to ten times faster than cddr+_g++. For less complicated polytopes, the speedup might be modest but one can expect the gmp version runs always faster.