submodule(fftpack) fftpack_rfft
contains
!> Forward transform of a real periodic sequence.
pure module function rfft_rk(x, n) result(result)
real(kind=rk), intent(in) :: x(:)
integer, intent(in), optional :: n
real(kind=rk), allocatable :: result(:)
integer :: lenseq, lensav, i
real(kind=rk), allocatable :: wsave(:)
if (present(n)) then
lenseq = n
if (lenseq <= size(x)) then
result = x(:lenseq)
else if (lenseq > size(x)) then
result = [x, (0.0_rk, i=1, lenseq - size(x))]
end if
else
lenseq = size(x)
result = x
end if
!> Initialize FFT
lensav = 2*lenseq + 15
allocate (wsave(lensav))
call dffti(lenseq, wsave)
!> Forward transformation
call dfftf(lenseq, result, wsave)
end function rfft_rk
end submodule fftpack_rfft
