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Public Enum FFTType
    FT_DIRECT
    FT_INVERSE
End Enum
Dim Rcoef(13) As Single, Icoef(13) As Single
Public Function FFT(Rdat() As Single, Idat() As Single, N_ As Long, Ft_Flag As FFTType) As Boolean
    Dim LogN As Long, i As Long, j As Long, N As Long, K As Long, io As Long, ie As Long, in_ As Long, nn As Long
    Dim ru As Single, iu As Single, rtp As Single, itp As Single, rtq As Single, itq As Single, rw As Single, _
        iw As Single, sr As Single
    If N_ > 16384 Or N_ < 1 Then Exit Function
    If Not ((Not ((N_) And ((N_) - 1))) And ((N_) > 1)) Then Exit Function
    LogN = Log2(N_)
    If LogN < 2 Or LogN > 14 Then Exit Function
    If Ft_Flag <> FT_DIRECT And Ft_Flag <> FT_INVERSE Then Exit Function
    nn = N_ \ 2
    ie = N_
    For N = 1 To LogN
        rw = Rcoef(LogN - N)
        iw = Icoef(LogN - N)
        If Ft_Flag = FT_INVERSE Then iw = -iw
        in_ = ie \ 2: ru = 1: iu = 0
        For j = 0 To in_ - 1
            For i = j To N_ - 1 Step ie
                io = i + in_
                rtp = Rdat(i) + Rdat(io)
                itp = Idat(i) + Idat(io)
                rtq = Rdat(i) - Rdat(io)
                itq = Idat(i) - Idat(io)
                Rdat(io) = rtq * ru - itq * iu
                Idat(io) = itq * ru + rtq * iu
                Rdat(i) = rtp: Idat(i) = itp
            Next
            sr = ru
            ru = ru * rw - iu * iw
            iu = iu * rw + sr * iw
        Next
        ie = ie \ 2
    Next
    j = 1
    For i = 1 To N_ - 1
        If i < j Then
            io = i - 1: in_ = j - 1
            rtp = Rdat(in_): itp = Idat(in_)
            Rdat(in_) = Rdat(io)
            Idat(in_) = Idat(io)
            Rdat(io) = rtp
            Idat(io) = itp
        End If
        K = nn
        Do While K < j
            j = j - K
            K = K \ 2
        Loop
        j = j + K
    Next
    If Ft_Flag = FT_INVERSE Then FFT = True: Exit Function
    rw = 1 / N_
    For i = 0 To N_ - 1
        Rdat(i) = Rdat(i) * rw
        Idat(i) = Idat(i) * rw
    Next
    FFT = True
End Function
Private Function Log2(ByVal Value As Long) As Long
    Dim N As Long, R As Long, O As Long
    If Value <= 0 Then Log2 = -1: Exit Function
    R = Value
    Do Until R <= 1
        N = N + 1
        O = R Mod 2
        If O > 0 Then Log2 = -1: Exit Function
        R = R \ 2
    Loop
    Log2 = N
End Function
Private Sub Class_Initialize()
    Dim N As Long, vRcoef As Variant, vIcoef As Variant
    vRcoef = Array(-1#, 0#, 0.707106781186547 _
          , 0.923879532511287, 0.98078528040323, 0.995184726672197 _
          , 0.998795456205172, 0.999698818696204, 0.999924701839145 _
          , 0.999981175282601, 0.999995293809576, 0.999998823451702 _
          , 0.999999705862882, 0.999999926465718)
    vIcoef = Array(0#, -1#, -0.707106781186547 _
         , -0.38268343236509, -0.195090322016128, -9.80171403295606E-02 _
         , -0.049067674327418, -2.45412285229122E-02, -1.22715382857199E-02 _
         , -6.1358846491544E-03, -3.0679567629659E-03, -1.5339801862847E-03 _
         , -7.669903187427E-04, -3.834951875714E-04)
    For N = 0 To 13
        Rcoef(N) = vRcoef(N)
        Icoef(N) = vIcoef(N)
    Next
End Sub