Quaternions

I have this. I don't really remember what I wrote it for:

Function RotatePointAroundVector(x#,y#,z#,u#,v#,w#,a#)
ux#=u*x
uy#=u*y
uz#=u*z
vx#=v*x
vy#=v*y
vz#=v*z
wx#=w*x
wy#=w*y
wz#=w*z
sa#=Sin(a)
ca#=Cos(a)
VECTOR_x#=u*(ux+vy+wz)+(x*(v*v+w*w)-u*(vy+wz))*ca+(-wy+vz)*sa
VECTOR_y#=v*(ux+vy+wz)+(y*(u*u+w*w)-v*(ux+wz))*ca+(wx-uz)*sa
VECTOR_z#=w*(ux+vy+wz)+(z*(u*u+v*v)-w*(ux+vy))*ca+(-vx+uy)*sa
End Function