在 VBA/VB6 中测试 NaN

Question

使用 VBA，我将字节数组中的 8 字节浮点数加载到 Double 中。一些数字将是 IEEE 754 NaN（即，如果您尝试使用 Debug.Print 打印它，您将看到 1.#QNAN）。我的问题是，如何测试 Double 中包含的数据是否是 NaN 而不是常规数字？

谢谢。

Answer 1

我发现最简单的方法是简单地将值更改为字符串并检查它是否等于 1.#QNAN。我从未遇到过不同类型的 NaN，但您始终可以将其扩展到您的 NaN 值的字符串值。

Function IsQNaN(number As Double) As Boolean

If CStr(number) = "1.#QNAN" Then
    IsQNAN = True
Else
    IsQNaN = False
End If

End Function

Answer 2

这是一组用于测试所有特殊值的函数：qnans 溢出、无穷大。将整个代码块放在一个模块中，你应该很高兴。

Option Explicit

Public Declare Sub CopyMemory Lib "kernel32" Alias _
    "RtlMoveMemory" (destination As Any, source As Any, _
    ByVal length As Long)


'***************************************************************
'Test to see if the functions work
'**************************************************************

Public Sub Test()
    'This tests the functions above against a set of doubles
    'note that this is not an exhaustive test since there are
    '18,014,398,509,481,984 special bit patterns. We test 7 of them
    'This test assumes that ThisWorkbook has a sheet with code name Sheet1
    Dim l(1 To 2) As Long, Vals(1 To 8) As Double, Oput As Variant
    Dim Num As Long

    'generate values to test
    DoubleFromHex &HFFF00000, 1, Vals(1) 'negative overflow
    DoubleFromHex &H7FF00000, 1, Vals(2) 'positive overflow
    DoubleFromHex &H7FF80000, 0, Vals(3) 'Positive QNaN
    DoubleFromHex &HFFF80000, 0, Vals(4) 'Indeterminate
    DoubleFromHex &HFFF80000, 1, Vals(5) 'Negative QNaN
    DoubleFromHex &H7FF00000, 0, Vals(6) 'Pos Infinity
    DoubleFromHex &HFFF00000, 0, Vals(7) 'Neg Infinity
    Vals(8) = 2.35345246654325E+27 'actual number generated using number pad fist mash alogorithm

    'dimension output
    ReDim Oput(1 To UBound(Vals) + 1, 1 To UBound(Vals) + 1)
    'fill test titles
    Oput(1, 2) = "IsOverflow"
    Oput(1, 3) = "IsPosQNaN"
    Oput(1, 4) = "IsNegQNaN"
    Oput(1, 5) = "IsIndetermiate"
    Oput(1, 6) = "IsPosInfinity"
    Oput(1, 7) = "IsNegInfinity"
    Oput(1, 8) = "IsSpecial"

    'fill number titles
    Oput(2, 1) = "Negative Overflow"
    Oput(3, 1) = "Positive Overflow"
    Oput(4, 1) = "Positive QNaN"
    Oput(5, 1) = "Indeterminate"
    Oput(6, 1) = "Negative QNaN"
    Oput(7, 1) = "Pos Infinity"
    Oput(8, 1) = "Neg Infinity"
    Oput(9, 1) = "Actual number"

    'perform tests
    For Num = 1 To 8
        Oput(Num + 1, 2) = IsOverflow(Vals(Num))
        Oput(Num + 1, 3) = IsPosQNaN(Vals(Num))
        Oput(Num + 1, 4) = IsNegQNaN(Vals(Num))
        Oput(Num + 1, 5) = IsIndetermiate(Vals(Num))
        Oput(Num + 1, 6) = IsPosInfinity(Vals(Num))
        Oput(Num + 1, 7) = IsNegInfinity(Vals(Num))
        Oput(Num + 1, 8) = IsSpecial(Vals(Num))
    Next Num

    'put to sheet
    Sheet1.Range("A1").Resize(UBound(Oput), UBound(Oput, 2)).Value = Oput
End Sub

'***************************************************************
'Functions
'**************************************************************
Public Function IsOverflow(Val As Double) As Boolean
    'This function returns true for doubles that VBA recognises as
    '<overflow>
    'it returns false for any other doubles
    'Doubles represented by <overflow> in VBA are more commonly known
    'as signalling NaNs

    Dim l(1 To 2) As Double

    'eliminate the positive and negative infinity
    If IsPosInfinity(Val) Then Exit Function
    If IsNegInfinity(Val) Then Exit Function

    'Convert the 64 bit double to 2 longs represented as doubles
    DeconstructDouble l, Val

    'test for positive overflow
    If l(2) >= USig(&H7FF00000) And l(2) <= USig(&H7FF7FFFF) Then
        IsOverflow = True
    ElseIf l(2) >= USig(&HFFF00000) And l(2) <= USig(&HFFF7FFFF) Then
        'test for negative overflow
        IsOverflow = True
    End If
End Function

Public Function IsPosQNaN(Val As Double) As Boolean
    'This function returns true for doubles that VBA recognises as
    '1.#QNAN (quiet not a number)
    'it returns false for any other doubles
    Dim l(1 To 2) As Double
    'Convert the 64 bit double to 2 longs represented as doubles
    DeconstructDouble l, Val
    'test for positive QNaN
    IsPosQNaN = (l(2) >= USig(&H7FF80000)) And (l(2) <= USig(&H7FFFFFFF))
End Function

Public Function IsNegQNaN(Val As Double) As Boolean
    'This function returns true for doubles that VBA recognises as
    '-1.#QNAN (negative quiet not a number)
    'it returns false for any other doubles
    Dim l(1 To 2) As Double
    'Convert the 64 bit double to 2 longs represented as doubles
    DeconstructDouble l, Val
    'test for negative QNaN
    IsNegQNaN = (l(2) >= USig(&HFFF80000)) And (l(1) <> 0)
End Function

Public Function IsIndetermiate(Val As Double) As Boolean
    'This function returns true for doubles that VBA recognises as
    ' -1.#IND (indeterminate)
    'it returns false for any other doubles
    Dim l(1 To 2) As Long
    'Convert the 64 bit double to 2 longs
    CopyMemory l(1), Val, 8
    'test for indeterminate
    IsIndetermiate = (l(2) = &HFFF80000) And ((l(1) = 0))
End Function

Public Function IsPosInfinity(Val As Double) As Boolean
    'returns true if and only if Val is recognised by VBA as 1.#INF
    Dim l(1 To 2) As Long
    'Convert the 64 bit double to 2 longs
    CopyMemory l(1), Val, 8
    'Check for negative infinity
    IsPosInfinity = (l(1) = 0) And (l(2) = &H7FF00000)
End Function

Public Function IsNegInfinity(Val As Double) As Boolean
    'returns true if and only if Val is recognised by VBA as -1.#INF
    Dim l(1 To 2) As Long
    'Convert the 64 bit double to 2 longs
    CopyMemory l(1), Val, 8
    'Check for negative infinity
    IsNegInfinity = (l(1) = 0) And (l(2) = &HFFF00000)
End Function

Public Function IsSpecial(Val As Double) As Boolean
    'returns true if Val is represented by VBA as any of
    '1.#INF,-1.#INF,-1.#IND,-1.#QNAN,1.#QNAN,<overflow>
    'ie returns true if and only if any of the other functions return true
    Dim l(1 To 2) As Double
    'Convert the 64 bit double to 2 longs represented as doubles
    DeconstructDouble l, Val
    IsSpecial = ((l(2) >= USig(&H7FF00000)) And (l(2) < USig(&H80000000))) Or l(2) >= USig(&HFFF00000)
End Function


'****************************************************
'Utility Functions
'****************************************************

Private Sub DoubleFromHex(Part1 As Long, Part2 As Long, Oput As Double)
    'convert a hex representation of a double into a double
    'can be used to generate doubles otherwise inaccessible by vba
    Dim l(1 To 2) As Long
    l(1) = Part2
    l(2) = Part1
    CopyMemory Oput, l(1), 8
End Sub

Private Function USig(l As Long) As Double
    'returns an unsigned value of a long as as double
    If l < 0 Then
        USig = 4294967296# + l
    Else
        USig = l
    End If
End Function

Private Sub DeconstructDouble(Oput() As Double, Iput As Double)
    'Splits the double's binary representation into 2 unsigned longs represented as doubles
    Dim l(1 To 2) As Long
    CopyMemory l(1), Iput, 8
    Oput(1) = USig(l(1))
    Oput(2) = USig(l(2))
End Sub

Answer 3

您可以通过将其十六进制值分配给两个 32 位长，然后使用 CopyMemory 将该值复制到双精度来生成双精度 QNaN

Public Declare Sub CopyMemory Lib "kernel32" Alias _
    "RtlMoveMemory" (destination As Any, source As Any, _
    ByVal length As Long)

Public Function QNaN() As Double
    Dim Oput As Double
    Dim l(1 To 2) As Long
    l(1) = &H7FFFFFFF
    l(2) = &HFFFFFFFF
    CopyMemory Oput, l(1), 8
    QNaN = Oput
End Function

Answer 4

NaN 在指数中有一个模式，您可以在它们仍在字节数组中时对其进行识别。具体来说，任何 NaN 都将具有全 1 的指数，任何 Infinity 也是如此，您可能也应该捕获它。

在双精度中，指数在最高位的两个字节中：

 SEEEEEEE EEEEMMMM MMM....

假设它们是 b(0) 和 b(1)：

  Is_A_Nan = ((b(0) And &H7F) = &H7F) And ((b(1) And &HF0) = &HF0)

这是航空代码，但你明白了。

如果您需要区分 SNaN、QNaN 和 Infinity，则需要深入研究，但这听起来对您来说不是问题。