subroutine kparfft(x1,y1,iabs)
c     
c
c calculates kpar * x and kpar * y
c
c or |kpar| * x and |kpar| * y    if iabs=1
c

      include 'itg.par'
      include 'itg.cmn'

      real x1(lz,mz,nz,nspecz),y1(lz,mz,nz,nspecz)
      integer l,iabs,ifail,m,n,imode,nmodes

      complex a(lz,mz*nz),b(lz,mz*nz),i
      real scale,work(4*lz*mz*nz)
      integer isign,nwork,ntablekp

      nmodes=ldb*nd*md
      scale=1.0/sqrt(float(ldb))
      nwork=4*lz*mz*nz
      ntablekp=100+2*lz
      i=(0.0,1.0)

      do m=1,md
         do n=1,nd
            imode=n+(m-1)*nd
            do l=1,ldb
              a(l,imode)=cmplx(x1(l,m,n,1),-y1(l,m,n,1))
            enddo
         enddo   
      enddo

      isign=-1
      call xmcfft(isign,ldb,md*nd,scale,a,1,lz,b,1,lz,tablekp,
     &   ntablekp,work,nwork)

      if (iabs.eq.0) then
       do imode=1,md*nd
          do l=1,ldb
            a(l,imode)=i*kpar(l)*b(l,imode)
          enddo
       enddo  
      else
       do imode=1,md*nd
          do l=1,ldb
            a(l,imode)=abs(kpar(l))*b(l,imode)
          enddo
       enddo
      endif

      isign=1
      call xmcfft(isign,ldb,md*nd,scale,a,1,lz,b,1,lz,tablekp,
     &   ntablekp,work,nwork)

      do m=1,md
         do n=1,nd
            imode=n+(m-1)*nd
            do l=1,ldb
              x1(l,m,n,1)=real(b(l,imode))
              y1(l,m,n,1)=-aimag(b(l,imode))
            enddo  
         enddo   
      enddo

      return
      end