Sub COSFT(Y(), N, ISIGN)
    THETA = 3.14159265358979 / N
    WR = 1#
    WI = 0#
    WPR = -2# * Sin(0.5 * THETA) ^ 2
    WPI = Sin(THETA)
    Sum = Y(1)
    M = N / 2
    For J = 1 To M - 1
        WTEMP = WR
        WR = WR * WPR - WI * WPI + WR
        WI = WI * WPR + WTEMP * WPI + WI
        Y1 = 0.5 * (Y(J + 1) + Y(N - J + 1))
        Y2 = (Y(J + 1) - Y(N - J + 1))
        Y(J + 1) = Y1 - WI * Y2
        Y(N - J + 1) = Y1 + WI * Y2
        Sum = Sum + WR * Y2
    Next J
    Call REALFT(Y, M, 1)
    Y(2) = Sum
    For J = 4 To N Step 2
        Sum = Sum + Y(J)
        Y(J) = Sum
    Next J
    If ISIGN = -1 Then
        EVEN = Y(1)
        ODD = Y(2)
        For I = 3 To N - 1 Step 2
            EVEN = EVEN + Y(I)
            ODD = ODD + Y(I + 1)
        Next I
        ENF0 = 2# * (EVEN - ODD)
        SUM0 = Y(1) - ENF0
        SUME = (2# * ODD / N) - SUM0
        Y(1) = 0.5 * ENF0
        Y(2) = Y(2) - SUME
        For I = 3 To N - 1 Step 2
            Y(I) = Y(I) - SUM0
            Y(I + 1) = Y(I + 1) - SUME
        Next I
    End If
End Sub