Halves it (at least it does in Dosbox). This is unfortunately a C-only implementation. I tried to get it to work with the mh spans duff device but that just brought me with colorful noise and crashes, so i'm using it with the initial qbism Drawspans16_C.
I got it to as well, since the span functions are similar.
While it does appear very grainy in screenshots, in motion it's not very noticably grainy and almost looks like Vquake.
I , i'll commit this later.

I almost want to do a release, but there are some strange bugs involving dynamic lighting and aspect ratio at the moment, and i'd also like to attempt implementing model interpolation from mh's tutorial again. My first attempt led to heavy crashes, and doing it now i'd have to start over as I have colored lighting stuff all over the model code.
andrewj's is something i'd like to get working again too (rendered the map in 15bpp, then dithered to 8bpp). It would be interesting to combine that, the kernel filtering, and the colored lighting all together to make one quasi-Unrealish renderer, and maybe bring all that up to having a 16bpp/24bpp option as well.