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qp2/src/csf/connected_to_ref.irp.f

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2021-02-17 14:59:25 +01:00
integer*8 function configuration_search_key(cfg,Nint)
use bitmasks
implicit none
BEGIN_DOC
! Returns an integer*8 corresponding to a determinant index for searching.
! The left-most 8 bits contain the number of open shells+1. This ensures that the CSF
! are packed with the same seniority.
END_DOC
integer, intent(in) :: Nint
integer(bit_kind), intent(in) :: cfg(Nint,2)
integer :: i, n_open_shells
integer*8 :: mask
i = shiftr(elec_alpha_num, bit_kind_shift)+1
configuration_search_key = int(shiftr(ior(cfg(i,1),cfg(i,2)),1)+sum(cfg),8)
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mask = int(Z'00FFFFFFFFFFFFFF',8)
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configuration_search_key = iand(mask,configuration_search_key)
n_open_shells = 1
do i=1,Nint
if (cfg(i,1) == 0_bit_kind) cycle
n_open_shells = n_open_shells + popcnt(cfg(i,1))
enddo
mask = n_open_shells
mask = shiftl(mask,56)
configuration_search_key = ior (mask,configuration_search_key)
end