I know that Builderboy made a decent raycaster, but since the caster made used of stairs, etc. it was too processor-intensive to including floor and ceiling textures.  If the area were entirely flat, is it possible to cast floors, walls and ceilings at the same time?  I read about how after a wall is drawn, the start-end coordinates of a ray of wall can be used to draw one ray of ceiling/floor

Thought it would be a fun ASM engine

I think you are thinking of Bwang, I never touched the nSpire

Yeah Bwang made a floorcaster and a separate raycaster. Not sure how fast both together are, but the floorcaster seemed pretty fast. I think wall textures could be reduced or something and it should be fine.

It would require Ndless, though, (or a mega speed boost in Lua from TI) because in Lua, with no texture it runs at 5 fps.