anchor.diff:  
     real(kind=real64) pure function atan2_ru(y,x)
       use, intrinsic :: iso_fortran_env, only : real64
  +    use numerical_constants, only : pi, pi2
       real(kind=real64), intent(in) :: x,y
       if(x == 0d0) then
         if(y == 0d0) then
  
positive.code:           ! Let the internal atan2 handle this case according to ieee
            atan2_rn=atan2(y,x)
          else
            atan2_rn=mb_pi
          end if
        else
          atan2_rn=atan_rn(y/x)
          if(x < 0d0) then
            atan2_rn=sign(mb_pi,y)+atan2_rn
          end if
        end if
      end if
  
negative.code:         atan2_rn=atan2(y,x)
  #endif
        else
          atan2_rn=sign(pi2,y)
        end if
      else
        if(y == 0d0) then
  