submodule(fftpack) fftpack_fft
contains
!> Forward transform of a complex periodic sequence.
pure module function fft_rk(x, n) result(result)
complex(kind=rk), intent(in) :: x(:)
integer, intent(in), optional :: n
complex(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, 0.0_rk), i=1, lenseq - size(x))]
end if
else
lenseq = size(x)
result = x
end if
!> Initialize FFT
lensav = 4*lenseq + 15
allocate (wsave(lensav))
call zffti(lenseq, wsave)
!> Forward transformation
call zfftf(lenseq, result, wsave)
end function fft_rk
end submodule fftpack_fft
