!-------------------------------------------------------------------------
      subroutine cfft3b(f,nr1,nr2,nr3,nr1x,nr2x,nr3x,isign)
!-----------------------------------------------------------------------
!     driver routine for 3d fft using fftw libraries (PG)
!
      use fftw_mod
      implicit none
!
      integer nr1, nr2, nr3, nr1x, nr2x, nr3x, isign
      complex*16 f(nr1x*nr2x*nr3x)
!
      real*8 fac
      integer ibid
!
! initialization variables
!
#ifdef B64
      integer*8 plan(2)
#else
      integer   plan(2)
#endif
      save plan
      data plan/0,0/
!
!
      if (nr1.ne.nr1x .or. nr2.ne.nr2x .or. nr3.ne.nr3x )               &
     &     call error('cfft3b','not implemented',1)
      if (isign.eq.1) then
         ibid=1
      else if (isign.eq.-1) then
         ibid=2
      else 
         call error('cfft3b','isign unexpected',isign)
      end if
!
      if (plan(ibid).eq.0)                                              &
     &     call fftw3d_f77_create_plan                                  &
     &        (plan(ibid),nr1,nr2,nr3,isign,FFTW_ESTIMATE+FFTW_IN_PLACE)
!     
      call fftwnd_f77_one(plan(ibid), f, 0)
!
      if (isign.eq.-1) then
         fac=1.0/dfloat(nr1*nr2*nr3)
         call SCAL(2*nr1*nr2*nr3, fac, f, 1)
      end if
!
      return
      end
!