Should fix the regression, and also speeds up table generation.
Tables tested on GNU/Linux+clang: they are identical to the ones prior
to 5495c7f2. ff_exp10 caused one slight change in one entry, 50000 became
50001 due to somewhat incorrect rounding.

Untested on ICC; passes FATE on GNU/Linux+gcc.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>