Created attachment 113231 [details]
Xnine testcase that checks the output of fract on texcoord.x*16-1/256

Beware that the part to d3dadapter9.so is hardcoded so you will need to change
it
This testcase renders a quad of two triangles that cover the entire screen (
256x16) , and outputs what happens with frac along the X axis on the 15th line,
where the triangle that has problems lies