subroutine passb3(ido, l1, cc, ch, wa1, wa2)
use fftpack_kind, only: dp => rk
implicit none
integer, intent(in) :: ido, l1
real(dp), intent(in) :: cc(ido, 3, l1), wa1(*), wa2(*)
real(dp), intent(out) :: ch(ido, l1, 3)
real(dp) :: ci2, ci3, cr2, cr3, di2, di3, &
dr2, dr3, ti2, tr2
integer :: i, k
real(dp), parameter :: taur = -0.5_dp
real(dp), parameter :: taui = sqrt(3.0_dp)/2.0_dp
if (ido /= 2) then
do k = 1, l1
do i = 2, ido, 2
tr2 = cc(i - 1, 2, k) + cc(i - 1, 3, k)
cr2 = cc(i - 1, 1, k) + taur*tr2
ch(i - 1, k, 1) = cc(i - 1, 1, k) + tr2
ti2 = cc(i, 2, k) + cc(i, 3, k)
ci2 = cc(i, 1, k) + taur*ti2
ch(i, k, 1) = cc(i, 1, k) + ti2
cr3 = taui*(cc(i - 1, 2, k) - cc(i - 1, 3, k))
ci3 = taui*(cc(i, 2, k) - cc(i, 3, k))
dr2 = cr2 - ci3
dr3 = cr2 + ci3
di2 = ci2 + cr3
di3 = ci2 - cr3
ch(i, k, 2) = wa1(i - 1)*di2 + wa1(i)*dr2
ch(i - 1, k, 2) = wa1(i - 1)*dr2 - wa1(i)*di2
ch(i, k, 3) = wa2(i - 1)*di3 + wa2(i)*dr3
ch(i - 1, k, 3) = wa2(i - 1)*dr3 - wa2(i)*di3
end do
end do
else
do k = 1, l1
tr2 = cc(1, 2, k) + cc(1, 3, k)
cr2 = cc(1, 1, k) + taur*tr2
ch(1, k, 1) = cc(1, 1, k) + tr2
ti2 = cc(2, 2, k) + cc(2, 3, k)
ci2 = cc(2, 1, k) + taur*ti2
ch(2, k, 1) = cc(2, 1, k) + ti2
cr3 = taui*(cc(1, 2, k) - cc(1, 3, k))
ci3 = taui*(cc(2, 2, k) - cc(2, 3, k))
ch(1, k, 2) = cr2 - ci3
ch(1, k, 3) = cr2 + ci3
ch(2, k, 2) = ci2 + cr3
ch(2, k, 3) = ci2 - cr3
end do
end if
end subroutine passb3
