subroutine dzfftf(n,r,Azero,a,b,Wsave)
!
! VERSION 3 JUNE 1979
!
use fftpack_kind
implicit none
real(rk) :: a , Azero , b , cf , cfm , r , Wsave
integer :: i , n , ns2 , ns2m
dimension r(*) , a(*) , b(*) , Wsave(*)
if ( n<2 ) then
Azero = r(1)
return
elseif ( n==2 ) then
Azero = 0.5_rk*(r(1)+r(2))
a(1) = 0.5_rk*(r(1)-r(2))
return
else
do i = 1 , n
Wsave(i) = r(i)
enddo
call dfftf(n,Wsave,Wsave(n+1))
cf = 2.0_rk/real(n, rk)
cfm = -cf
Azero = 0.5_rk*cf*Wsave(1)
ns2 = (n+1)/2
ns2m = ns2 - 1
do i = 1 , ns2m
a(i) = cf*Wsave(2*i)
b(i) = cfm*Wsave(2*i+1)
enddo
if ( mod(n,2)==1 ) return
a(ns2) = 0.5_rk*cf*Wsave(n)
b(ns2) = 0.0_rk
endif
end subroutine dzfftf
