Function LongToFloat(X)
 Dim S, E, F

 S = -(X <  0 )
 E = (X And &H7F800000) \ &H800000
 F = X And &H7FFFFF
 
 If ( 0  < E) And (E <  255 ) Then
    LongToFloat = (- 1 ) ^ S *  2  ^ (E -  127 ) * ((F Or &H800000) / &H800000)
 ElseIf E =  0  Then
    If F =  0  Then
       If S =  0  Then
          LongToFloat =  0  'плюс ноль
       Else
          LongToFloat = - 0  'минус ноль
       End If
    Else '(E = 0) And (F <> 0)
       LongToFloat = (- 1 ) ^ S *  2  ^ (- 126 ) * (F / &H800000)
    End If
 Else 'E = 255
    If F =  0  Then
       If S =  0  Then
          LongToFloat =  0  'плюс бесконечность
       Else
          LongToFloat = - 0  'минус бесконечность
       End If
    Else '(E = 255) And (F <> 0)
       LongToFloat =  0  'не-число - NaN - Not a Number
    End If
 End If
End Function

Function FourBytesToLong(B0, B1, B2, B3)
 If B3 <=  127  Then
    FourBytesToLong = B3 * &H1000000 + B2 * &H10000 + B1 * &H100& + B0
 Else
    FourBytesToLong = -(( 255  - B3) * &H1000000 + ( 255  - B2) * &H10000 + _
                        ( 255  - B1) * &H100& + ( 255  - B0) +  1 )
 End If
End Function

Sub Test()
 Dim L
 L = LongToFloat(FourBytesToLong(&HDA, &H0F, &H49, &H40)) 'число Пи, по идее
End Sub

Function FourBytesToLong(B0, B1, B2, B3)
 If B3 <=  127  Then
    FourBytesToLong = B3 * &H1000000 + B2 * &H10000 + B1 * &H100& + B0
 Else
    FourBytesToLong = -(( 255  - B3) * &H1000000 + ( 255  - B2) * &H10000 + _
                        ( 255  - B1) * &H100& + ( 255  - B0)) -  1 
 End If
End Function