Prueba de NaN en VBA/VB6

Question

Uso de VBA Estoy cargando un número de punto flotante de 8 bytes de una matriz de bytes en un Doble. Algunos números serán IEEE 754 NaN (es decir, si intenta imprimirlo con Debug.Print, verá 1. # QNAN). Mi pregunta es, ¿cómo puedo probar si los datos contenidos en el Doble son un NaN a diferencia de un número regular?

Gracias.

Answer 1

NaN de tener un patrón en el exponente que se puede identificar mientras están todavía en la matriz de bytes. Específicamente, cualquier NaN tendrá un exponente de todos los 1, al igual que cualquier Infinity, que probablemente también deberías atrapar.

En un doble, el exponente es en el más alto orden dos bytes:

SEEEEEEE EEEEMMMM MMM.... 

Asumir esos son b (0) y B (1):

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

Eso es código aire, Pero se entiende la idea.

Si es necesario distinguir entre SNAN, QNAN, e Infinity tendrá que mirar más profundamente, pero no suena como eso es un problema para usted.

Answer 2

Puede generar un doble QNAN asignando su valor hexadecimal de dos 32 anhela bits y luego copiar el valor al doble usando CopyMemory

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

Aquí es un conjunto de funciones de prueba para todos los valores especiales: qnans se desborda, infinitos. Pon todo el bloque de código en un módulo y deberías estar listo para continuar.

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

He encontrado que el método más fácil es simplemente cambiar el valor de una cadena y comprobar si es igual a 1. # QNAN. Nunca me encontré con un tipo diferente de NaN, pero siempre puedes extenderlo a cualquier valor de cadena de tu valor de NaN.

Function IsQNaN(number As Double) As Boolean 

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

End Function