We do not need to calculate the reflection vector (r). 

The angle between the halfway vector and the normal vector is twice the angle between the reflection vector (r) and the view vector (v) (Ψ = 2Φ). 

The model uses a halfway vector that is a unit vector exactly halfway between the view direction and the light direction.

The angle between the halfway vector and the surface normal never exceeds 90 degrees (thus, there is no artifact).