Not so much a bug, as slow!

[britlion]

If SIN, COS, RND were libraries and not functions

I just realised - you do know I did all of those as libraries in the wiki, right?
Game versions, however; not very accurate. You may want to look at stuff like <!-- m --><a class="postlink" href="http://www.andreadrian.de/oldcpu/sincos.z80">http://www.andreadrian.de/oldcpu/sincos.z80</a><!-- m --> for better versions!