VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   8490
   ClientLeft      =   1665
   ClientTop       =   345
   ClientWidth     =   6090
   LinkTopic       =   "Form1"
   ScaleHeight     =   8490
   ScaleWidth      =   6090
   Begin VB.CommandButton Command1 
      Caption         =   "Command1"
      Height          =   375
      Left            =   4680
      TabIndex        =   0
      Top             =   120
      Width           =   1335
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Private Sub Command1_Click()
    'PROGRAM D12R2
    'Driver for routine TWOFFT
    N = 32
    N2 = 2 * N
    PER = 8#
    PI = 3.1415926
    Dim DATA1(32), DATA2(32), FFT1(64), FFT2(64)
    For I = 1 To N
        X = 2# * PI * I / PER
        DATA1(I) = CInt(Cos(X))
        DATA2(I) = CInt(Sin(X))
    Next I
    Call TWOFFT(DATA1(), DATA2(), FFT1(), FFT2(), N)
    Print Tab(5); "Fourier transform of first function:"
    Call PRNTFT(FFT1(), N2)
    Print Tab(5); "Fourier transform of second function:"
    Call PRNTFT(FFT2(), N2)
    'Invert transform
    ISIGN = -1
    Call FOUR1(FFT1(), N, ISIGN)
    Print Tab(5); "Inverted transform = first function:"
    Call PRNTFT(FFT1(), N2)
    Call FOUR1(FFT2(), N, ISIGN)
    Print Tab(5); "Inverted transform = second function:"
    Call PRNTFT(FFT2(), N2)
End Sub
Sub PRNTFT(DATA(), N2)
    Print Tab(5); "n       Real(n)     Imag.(n)      Real(N-n)    Imag.(N-n)"
    Print Tab(5); Format$(0, "0");
    Print Tab(12); Format$(DATA(1), "##.#####0");
    Print Tab(25); Format$(DATA(2), "##.#####0");
    Print Tab(38); Format$(DATA(1), "##.#####0");
    Print Tab(51); Format$(DATA(2), "##.#####0")
    For I = 3 To (N2 / 2) + 1 Step 2
        M = (I - 1) / 2
        NN2 = N2 + 2 - I
        Print Tab(5); Format$(M, "0");
        Print Tab(12); Format$(DATA(I), "##.#####0");
        Print Tab(25); Format$(DATA(I + 1), "##.#####0");
        Print Tab(38); Format$(DATA(NN2), "##.#####0");
        Print Tab(51); Format$(DATA(NN2 + 1), "##.#####0")
    Next I
End Sub
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
Sub FOUR1(DATA(), NN, ISIGN)
      N = 2 * NN
      J = 1
      For I = 1 To N Step 2
          If J > I Then
              TEMPR = DATA(J)
              TEMPI = DATA(J + 1)
              DATA(J) = DATA(I)
              DATA(J + 1) = DATA(I + 1)
              DATA(I) = TEMPR
              DATA(I + 1) = TEMPI
          End If
          M = N / 2
          While M >= 2 And J > M
              J = J - M
              M = M / 2
          Wend
          J = J + M
      Next I
      MMAX = 2
      While N > MMAX
          ISTEP = 2 * MMAX
          THETA = 6.28318530717959 / (ISIGN * MMAX)
          WPR = -2# * Sin(0.5 * THETA) ^ 2
          WPI = Sin(THETA)
          WR = 1#
          WI = 0#
          For M = 1 To MMAX Step 2
              For I = M To N Step ISTEP
                  J = I + MMAX
                  TEMPR = CSng(WR) * DATA(J) - CSng(WI) * DATA(J + 1)
                  TEMPI = CSng(WR) * DATA(J + 1) + CSng(WI) * DATA(J)
                  DATA(J) = DATA(I) - TEMPR
                  DATA(J + 1) = DATA(I + 1) - TEMPI
                  DATA(I) = DATA(I) + TEMPR
                  DATA(I + 1) = DATA(I + 1) + TEMPI
              Next I
              WTEMP = WR
              WR = WR * WPR - WI * WPI + WR
              WI = WI * WPR + WTEMP * WPI + WI
          Next M
          MMAX = ISTEP
      Wend
End Sub