Good luck with writing a software renderer that runs at an acceptable framerate! Even for my pixelart game engine, I had to tap into the dark magic of SSE2 extensions, at least I could write a pretty fast Mode 7 renderer (the only thing that will remain on the CPU so far after the OpenGL transition, due to it otherwise needing compute stuff).
Good luck with writing a software renderer that runs at an acceptable framerate! Even for my pixelart game engine, I had to tap into the dark magic of SSE2 extensions, at least I could write a pretty fast Mode 7 renderer (the only thing that will remain on the CPU so far after the OpenGL transition, due to it otherwise needing compute stuff).