使用 VBA，我将字节数组中的 8 字节浮点数加载到 Double 中。有些数字将是 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。
NaN 在指数中具有一种模式，您可以在它们仍在字节数组中时识别它们。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。
在双精度型中，指数位于最高位两个字节中：
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，您需要更深入地研究，但这听起来对您来说不是问题。
我发现最简单的方法就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 NaN 值的任何字符串值。
Function IsQNaN(number As Double) As Boolean
If CStr(number) = "1.#QNAN" Then
IsQNAN = True
Else
IsQNaN = False
End If
End Function
这是一组用于测试所有特殊值的函数：qnans 溢出、无穷大。将整个代码块放入一个模块中，您就可以开始了。
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
您可以通过将其十六进制值分配给两个 32 位长整型，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