subroutine passb2(ido, l1, cc, ch, wa1)
use fftpack_kind, only: dp => rk
implicit none
integer, intent(in) :: ido, l1
real(dp), intent(in) :: cc(ido, 2, l1), wa1(*)
real(dp), intent(out) :: ch(ido, l1, 2)
real(dp) :: ti2, tr2
integer :: i, k
if (ido > 2) then
do concurrent(k=1:l1, i=2:ido:2)
ch(i - 1, k, 1) = cc(i - 1, 1, k) + cc(i - 1, 2, k)
tr2 = cc(i - 1, 1, k) - cc(i - 1, 2, k)
ch(i, k, 1) = cc(i, 1, k) + cc(i, 2, k)
ti2 = cc(i, 1, k) - cc(i, 2, k)
ch(i, k, 2) = wa1(i - 1)*ti2 + wa1(i)*tr2
ch(i - 1, k, 2) = wa1(i - 1)*tr2 - wa1(i)*ti2
end do
else
do concurrent(k=1:l1)
ch(1, k, 1) = cc(1, 1, k) + cc(1, 2, k)
ch(1, k, 2) = cc(1, 1, k) - cc(1, 2, k)
ch(2, k, 1) = cc(2, 1, k) + cc(2, 2, k)
ch(2, k, 2) = cc(2, 1, k) - cc(2, 2, k)
end do
end if
end subroutine passb2
