previous attempt tried to use shifts to get 0.4 to 0.2 or 0.8 and multiplication to get -0.8, forgetting that the multiplication would also turn 0.4 into 0 along the way. oops. I got ratholed on the mathematical approach, but a very straightforward lookup table can get more done.
Reviewed-on: pyrex/chameleonic#14
Co-authored-by: Kistaro Windrider <kistaro@gmail.com>
Co-committed-by: Kistaro Windrider <kistaro@gmail.com>
