Indeed, for big integers, looking at |x-x'|<eps leads to false
positive, because of the precision (*); it is better to to look at
|1-x/x'|<eps

(*) the precision (-p 6) influence the comparison, because the SUT
currently sends its result via a socket and truncate the result
(which is probably a bad idea).

nb : the exec time explose (x3), but for an external (unknown) reason
(undoing the change leads to the same exec time ~800s).