code: def _orient3dfast(plane, pd):
      
      pa, pb, pc = plane
      adx = pa[0] - pd[0]
      bdx = pb[0] - pd[0]
      cdx = pc[0] - pd[0]
      ady = pa[1] - pd[1]
      bdy = pb[1] - pd[1]
      cdy = pc[1] - pd[1]
      adz = pa[2] - pd[2]
      bdz = pb[2] - pd[2]
      cdz = pc[2] - pd[2]
  
      return (adx * (bdy * cdz - bdz * cdy)
              + bdx * (cdy * adz - cdz * ady)
              + cdx * (ady * bdz - adz * bdy))
docs: Performs a fast 3D orientation test.
  
      Parameters
      ----------
      plane: (3,3) float, three points in space that define a plane
      pd:    (3,)  float, a single point
  
      Returns
      -------
      result: float, if greater than zero then pd is above the plane through
                     the given three points, if less than zero then pd is below
                     the given plane, and if equal to zero then pd is on the
                     given plane.