Help Please

I was working on a cube based preset with a sphere inside that bounces off the sides, (it might be overdone, but it's my first time doing it). I am having trouble making the sphere bounce off the walls correctly, my way may not be the mathamaticly correct way of doing this, but I was hoping somebody could help me fix my math out. Uses AVS 2.7pre3- globalvars, constants.

heh, i dont understand the code, i even havent tryed doing something like this... but what i can say that this way isnt correct :P

it shouldnt be had to make the sphere stay in the cube allway and later figure out the bouncing