subroutine drftf1 (n,c,ch,wa,ifac)
      double precision c(1), ch(1), wa(1)
      integer ifac(1)
c
      nf = ifac(2)
      na = 1
      l2 = n
      iw = n
      do 111 k1=1,nf
         kh = nf-k1
         ip = ifac(kh+3)
         l1 = l2/ip
         ido = n/l2
         idl1 = ido*l1
         iw = iw-(ip-1)*ido
         na = 1-na
         if (ip .ne. 4) go to 102
c
         ix2 = iw+ido
         ix3 = ix2+ido
         if (na .ne. 0) go to 101
         call dradf4 (ido,l1,c,ch,wa(iw),wa(ix2),wa(ix3))
         go to 110
  101    call dradf4 (ido,l1,ch,c,wa(iw),wa(ix2),wa(ix3))
         go to 110
c
  102    if (ip .ne. 2) go to 104
         if (na .ne. 0) go to 103
         call dradf2 (ido,l1,c,ch,wa(iw))
         go to 110
  103    call dradf2 (ido,l1,ch,c,wa(iw))
         go to 110
c
  104    if (ip .ne. 3) go to 106
         ix2 = iw+ido
         if (na .ne. 0) go to 105
         call dradf3 (ido,l1,c,ch,wa(iw),wa(ix2))
         go to 110
  105    call dradf3 (ido,l1,ch,c,wa(iw),wa(ix2))
         go to 110
c
  106    if (ip .ne. 5) go to 108
         ix2 = iw+ido
         ix3 = ix2+ido
         ix4 = ix3+ido
         if (na .ne. 0) go to 107
         call dradf5 (ido,l1,c,ch,wa(iw),wa(ix2),wa(ix3),wa(ix4))
         go to 110
  107    call dradf5 (ido,l1,ch,c,wa(iw),wa(ix2),wa(ix3),wa(ix4))
         go to 110
c
  108    if (ido .eq. 1) na = 1-na
         if (na .ne. 0) go to 109
         call dradfg (ido,ip,l1,idl1,c,c,c,ch,ch,wa(iw))
         na = 1
         go to 110
  109    call dradfg (ido,ip,l1,idl1,ch,ch,ch,c,c,wa(iw))
         na = 0
c
  110    l2 = l1
  111 continue
c
      if (na .eq. 1) return
      do 112 i=1,n
         c(i) = ch(i)
  112 continue
c
      return
      end