if you feed cosp a 2 itll return to the first value, since it uses cosine which is periodic, it wont continue into No man's land like lerp/qarp/cubic, since its essentially cos(t*180) or something like that controlling an interpolation
cosp(a,b,0)=a
cosp(a,b,1)=b
cosp(a,b,2)=a
but its a pure A-B-A sine loop, not a hard bounce like rojos, that would have to be a kinda ABScosp sysexp.
and to make rojos faster its better to just do
lerp(a.x,b.x,abs(sin(lerp(0,180,t))))
id imagine.