在VBA/VB6中測試NaN

Question

使用VBA我將8字節的浮點數從字節數組加載到Double中。某些數字將是IEEE 754 NaN（即如果您嘗試使用Debug.Print打印它，您將看到1.＃QNAN）。我的問題是，如何測試Double中包含的數據是否是NaN而不是常規數字？

謝謝。

Answer 1

NaN在指數中有一個模式，可以在它們仍然在字節數組中時識別。具體來說，任何NaN都將具有全1的指數，就像您可能應該陷入的任何Infinity一樣。

在雙，指數是在最上位的兩個字節：

SEEEEEEE EEEEMMMM MMM.... 

假設那些是b（0）和b（1）：

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

這是空氣代碼，但你明白了。

如果您需要區分SNaN，QNaN和Infinity，則需要更深入一點，但聽起來不像是您的問題。

Answer 2

您可以通過其十六進制值分配給兩個32位多頭，然後將值複製到雙用CopyMemory的

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 3

這裏產生一個雙QNAN是功能測試所有特殊值一套房： qnans溢出，無限。把整個代碼塊放在一個模塊中，你應該很好走。

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 4

我發現最簡單的方法是簡單地將該值更改爲字符串，並檢查它是否等於1.＃QNAN。我從來沒有遇到過不同類型的NaN，但是你總是可以將它擴展到你的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