right_most_zero Function

    integer function right_most_zero(i, n_orbs)
        ! gives the position of the right most zero with atleast one 1
        ! right of it in an integer bit representation, up to a input
        ! dependent orbital n_orbs
        integer(n_int), intent(in) :: i
        integer, intent(in) :: n_orbs
        integer, allocatable :: nZeros(:), nOnes(:)
        integer(n_int) :: j

        ! first truncate the integer to be save..
        ! set all the ones left of n_orbs to 0
        j = iand(i, int(maskr(n_orbs), n_int))

        ! be sure to avoid the edge case:
        if (j == 0_n_int) then
            right_most_zero = -1
            return
        end if

        ! i could misuse the decode_bit_det functionality
        allocate(nZeros(popcnt(not(j))))
        allocate(nOnes(popcnt(j)))

        ! but exclude the unnecessary 0 left of n_orbs..
        call decode_bit_det(nZeros, [not(j)])
        call decode_bit_det(nOnes, [j])

        ! in this way to encode it.. the right most 0 is then the minumum
        ! in nZeros which is bigger then the minumum in nOnes
        right_most_zero = minval(nZeros, nZeros > minval(nOnes))

    end function right_most_zero