[PPL-devel] Bug in PolyBase::generators() and maybe somewhere else

[Roberto Bagnara]

I have just added a new program, `generators2' to the `tests' directory.
It shows a bug in PolyBase::generators() when it is invoked on a polyhedron
that is "semantically empty" and not "syntactically empty".  The analysis
is easy: since generators are not up to date, we invoke update_generators(),
which returns false because the polyhedron was found to be empty.
We ignore the return value of update_generators() and happily call
obtain_sorted_generators()... BOOM!

231 
   if (!generators_are_up_to_date())
232 
     update_generators();
233 

234 
   // We insist in returning a sorted system of generators.
235 
   obtain_sorted_generators();

At a first sight, there are other places where the return value
of update_generators() is ignored, and this is not a nice thing.
Ciao

     Roberto

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it