subroutine dcost(n,x,Wsave)
use fftpack_kind
implicit none
real(rk) :: c1 , t1 , t2 , tx2 , Wsave , x , x1h , x1p3 , &
xi , xim2
integer :: i , k , kc , modn , n , nm1 , np1 , ns2
dimension x(*) , Wsave(*)
nm1 = n - 1
np1 = n + 1
ns2 = n/2
if ( n<2 ) return
if ( n==2 ) then
x1h = x(1) + x(2)
x(2) = x(1) - x(2)
x(1) = x1h
return
elseif ( n>3 ) then
c1 = x(1) - x(n)
x(1) = x(1) + x(n)
do k = 2 , ns2
kc = np1 - k
t1 = x(k) + x(kc)
t2 = x(k) - x(kc)
c1 = c1 + Wsave(kc)*t2
t2 = Wsave(k)*t2
x(k) = t1 - t2
x(kc) = t1 + t2
enddo
modn = mod(n,2)
if ( modn/=0 ) x(ns2+1) = x(ns2+1) + x(ns2+1)
call dfftf(nm1,x,Wsave(n+1))
xim2 = x(2)
x(2) = c1
do i = 4 , n , 2
xi = x(i)
x(i) = x(i-2) - x(i-1)
x(i-1) = xim2
xim2 = xi
enddo
if ( modn/=0 ) x(n) = xim2
return
endif
x1p3 = x(1) + x(3)
tx2 = x(2) + x(2)
x(2) = x(1) - x(3)
x(1) = x1p3 + tx2
x(3) = x1p3 - tx2
end subroutine dcost
