CALCUL DE LA FONCTION LOGARITHME

Public Function ZLog10(X) As Double
    Dim Wi As Integer
    Dim N, N1, N2, N3 As Double
    Dim P As Integer
    Dim Sg As Boolean
    Sg = True
    If X <= 0 Then
        xx = MsgBox("Valeur négative ou nulle interdite", vbCritical, "Calcul du Log")
        Exit Function
    End If
    
    If X < 1 And X > 0 Then
        X = 1 / X
        Sg = False
    End If
    
    N1 = X
    P = 0
    N2 = 0
    N3 = 1
    While P < 16
        Wi = 0
        N = N1
        While N >= 10
            N = N / 10
            Wi = Wi + 1
        Wend
        N1 = N * N
        N1 = N1 * N1
        N1 = N1 * N
        N1 = N1 * N1
        N2 = N2 + Wi / N3
        P = P + 1
        N3 = N3 * 10
    Wend
    If Not Sg Then
        N2 = -N2
    End If
    
    ZLog10 = N2
End Function

Public Function ZLog2(X) As Double
    Dim Wi, Wj, Wk, Wl As Integer
    Dim N, N1, N2, N3 As Double
    Dim P As Integer
    Dim Sg As Boolean
    'log(2)=0.693147180559945309417232121458176568075500134360255254120678
    Dim WLOG2 As Double
    WLOG2 = 0.693147180559945
    Sg = True
    If X <= 0 Then
        xx = MsgBox("Valeur négative ou nulle interdite", vbCritical, "Calcul du Log")
        Exit Function
    End If
    
    If X < 1 And X > 0 Then
        X = 1 / X
        Sg = False
    End If
    
    N1 = X
    P = 0
    N2 = 0
    N3 = 1
    While P < 60
        Wi = 0
        N = N1
        While N >= 2
            N = N / 2
            Wi = Wi + 1
        Wend
        N1 = N * N
        N2 = N2 + Wi / N3
        P = P + 1
        N3 = N3 * 2
    Wend
    If Not Sg Then
        N2 = -N2
    End If
    
    ZLog2 = N2 * WLOG2
End Function

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