passb2 Subroutine

      subroutine passb2(Ido,l1,Cc,Ch,Wa1)
      use fftpack_kind
      implicit none
      real(rk) :: Cc , Ch , ti2 , tr2 , Wa1
      integer :: i , Ido , k , l1
      dimension Cc(Ido,2,l1) , Ch(Ido,l1,2) , Wa1(*)
      if ( Ido>2 ) then
         do k = 1 , l1
            do i = 2 , Ido , 2
               Ch(i-1,k,1) = Cc(i-1,1,k) + Cc(i-1,2,k)
               tr2 = Cc(i-1,1,k) - Cc(i-1,2,k)
               Ch(i,k,1) = Cc(i,1,k) + Cc(i,2,k)
               ti2 = Cc(i,1,k) - Cc(i,2,k)
               Ch(i,k,2) = Wa1(i-1)*ti2 + Wa1(i)*tr2
               Ch(i-1,k,2) = Wa1(i-1)*tr2 - Wa1(i)*ti2
            enddo
         enddo
      else
         do k = 1 , l1
            Ch(1,k,1) = Cc(1,1,k) + Cc(1,2,k)
            Ch(1,k,2) = Cc(1,1,k) - Cc(1,2,k)
            Ch(2,k,1) = Cc(2,1,k) + Cc(2,2,k)
            Ch(2,k,2) = Cc(2,1,k) - Cc(2,2,k)
         enddo
      end if
      end subroutine passb2