Well, this code was written in fenix some time ago so I had to do REALLY weird things to avoid some old bugs. (abs wasn't even working properly with floats back then... tough times). The drawing functions were meant for higher resolutions, where small sized tile slices became less than 1px wide and wouldn't draw and far away walls became invisible, so fog-like brown lines would fill these gaps. That's why there are various sized tile slices, not the right thing to do, but the way it would work fast enough back then.
Over 100 fps is a huge boost, for sure! I should update myself regarding the current divlike scene, I'm glad to see things are moving forward over here.