Sub TWOFFT(DATA1(), DATA2(), FFT1(), FFT2(), N)
    C1R = 0.5
    C1I = 0#
    C2R = 0#
    C2I = -0.5
    For J = 1 To N
        FFT1(2 * J - 1) = DATA1(J)
        FFT1(2 * J) = DATA2(J)
    Next J
    Call FOUR1(FFT1(), N, 1)
    FFT2(1) = FFT1(2)
    FFT2(2) = 0#
    FFT1(2) = 0#
    N2 = 2 * (N + 2)
    For J = 2 To N / 2 + 1
        J2 = 2 * J
        CONJR = FFT1(N2 - J2 - 1)
        CONJI = -FFT1(N2 - J2)
        H1R = C1R * (FFT1(J2 - 1) + CONJR) - C1I * (FFT1(J2) + CONJI)
        H1I = C1I * (FFT1(J2 - 1) + CONJR) + C1R * (FFT1(J2) + CONJI)
        H2R = C2R * (FFT1(J2 - 1) - CONJR) - C2I * (FFT1(J2) - CONJI)
        H2I = C2I * (FFT1(J2 - 1) - CONJR) + C2R * (FFT1(J2) - CONJI)
        FFT1(J2 - 1) = H1R
        FFT1(J2) = H1I
        FFT1(N2 - J2 - 1) = H1R
        FFT1(N2 - J2) = -H1I
        FFT2(J2 - 1) = H2R
        FFT2(J2) = H2I
        FFT2(N2 - J2 - 1) = H2R
        FFT2(N2 - J2) = -H2I
    Next J
End Sub