subroutine radf3(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, l1, 3), wa1(*), wa2(*)
real(dp), intent(out) :: ch(ido, 3, l1)
real(dp) :: ci2, cr2, di2, di3, dr2, dr3, &
ti2, ti3, tr2, tr3
integer :: i, ic, idp2, k
real(dp), parameter :: taur = -0.5_dp
! note: original comment said this was -sqrt(3)/2 but value was 0.86602540378443864676d0
real(dp), parameter :: taui = sqrt(3.0_dp)/2.0_dp
do concurrent(k=1:l1)
cr2 = cc(1, k, 2) + cc(1, k, 3)
ch(1, 1, k) = cc(1, k, 1) + cr2
ch(1, 3, k) = taui*(cc(1, k, 3) - cc(1, k, 2))
ch(ido, 2, k) = cc(1, k, 1) + taur*cr2
end do
if (ido == 1) return
idp2 = ido + 2
do concurrent(k=1:l1, i=3:ido:2)
ic = idp2 - i
dr2 = wa1(i - 2)*cc(i - 1, k, 2) + wa1(i - 1)*cc(i, k, 2)
di2 = wa1(i - 2)*cc(i, k, 2) - wa1(i - 1)*cc(i - 1, k, 2)
dr3 = wa2(i - 2)*cc(i - 1, k, 3) + wa2(i - 1)*cc(i, k, 3)
di3 = wa2(i - 2)*cc(i, k, 3) - wa2(i - 1)*cc(i - 1, k, 3)
cr2 = dr2 + dr3
ci2 = di2 + di3
ch(i - 1, 1, k) = cc(i - 1, k, 1) + cr2
ch(i, 1, k) = cc(i, k, 1) + ci2
tr2 = cc(i - 1, k, 1) + taur*cr2
ti2 = cc(i, k, 1) + taur*ci2
tr3 = taui*(di2 - di3)
ti3 = taui*(dr3 - dr2)
ch(i - 1, 3, k) = tr2 + tr3
ch(ic - 1, 2, k) = tr2 - tr3
ch(i, 3, k) = ti2 + ti3
ch(ic, 2, k) = ti3 - ti2
end do
end subroutine radf3
