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std::numeric_limits::signaling_NaN

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std::numeric_limits
 
static T signaling_NaN()
(até C + 11)
static constexpr T signaling_NaN()
(a partir do C++ 11)
Retorna o valor especial "sinalização não-um-número", representado pelo T tipo de ponto flutuante. Só faz sentido se std::numeric_limits<T>::has_signaling_NaN == true. Em IEEE 754, a representação binária mais comum de números de ponto flutuante, qualquer valor de todos os bits de expoente do conjunto e pelo menos um bit do conjunto representa uma fracção NaN. É definida pela implementação que os valores da fração representam NaNs tranquilos ou de sinalização, e se o bit de sinal é significativa.
Original:
Returns the special value "signaling não-um-número", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_signaling_NaN == true. In IEEE 754, the most common binary representation of floating-point numbers, any value with all bits of the exponent set and at least one bit of the fraction set represents a NaN. It is implementation-defined which values of the fraction represent quiet or signaling NaNs, and whether the sign bit is meaningful.
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Índice

[editar] Valor de retorno

T std::numeric_limits<T>::quiet_NaN()
/* non-specialized */ T();
bool false
char 0
signed char 0
unsigned char 0
wchar_t 0
char16_t 0
char32_t 0
short 0
unsigned short 0
int 0
unsigned int 0
long 0
unsigned long 0
long long 0
unsigned long long 0
float
definida pela implementação
Original:
implementation-defined
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double
definida pela implementação
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implementation-defined
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long double
definida pela implementação
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implementation-defined
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[editar] Exceções

noexcept specification:  
noexcept
  (a partir do C++ 11)

[editar] Notas

A NaN nunca compara igual a si mesma. Copiando um NaN não pode preservar a sua representação pouco.
Original:
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
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Quando um NaN sinalização é usado como um argumento para uma expressão aritmética, a excepção de ponto flutuante adequada, podem ser levantadas e a NaN é "acalmado", isto é, a expressão retorna um NaN silencioso.
Original:
When a signaling NaN is used as an argument to an arithmetic expression, the appropriate floating-point exception may be raised and the NaN is "quieted", that is, the expression returns a quiet NaN.
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[editar] Exemplo

Demonstra o uso de um NaN sinalização para aumentar uma exceção de ponto flutuante
Original:
Demonstrates the use of a signaling NaN to raise a floating-point exception
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#include <iostream>
#include <limits>
#include <cfenv>
#pragma STDC_FENV_ACCESS on
void show_fe_exceptions()
{
    int n = std::fetestexcept(FE_ALL_EXCEPT);
    if(n & FE_INVALID) std::cout << "FE_INVALID is raised\n";
    else if(n == 0)    std::cout << "no exceptions are raised\n";
    std::feclearexcept(FE_ALL_EXCEPT);
}
int main()
{
    double snan = std::numeric_limits<double>::signaling_NaN();
    std::cout << "After sNaN was obtained ";
    show_fe_exceptions();
    double qnan = snan * 2.0;
    std::cout << "After sNaN was multiplied by 2 ";
    show_fe_exceptions();
    double qnan2 = qnan * 2.0;
    std::cout << "After the quieted NaN was multiplied by 2 ";
    show_fe_exceptions();
    std::cout << "The result is " << qnan2 << '\n';
}

Output:

After sNaN was obtained no exceptions are raised
After sNaN was multiplied by 2 FE_INVALID is raised
After the quieted NaN was multiplied by 2 no exceptions are raised
The result is nan

[editar] Veja também

identifica tipos de ponto flutuante que podem representar o valor especial "de sinalização não-número um" (NaN)
Original:
identifies floating-point types that can represent the special value "signaling not-a-number" (NaN)
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(membro estático público constante) [edit]
[estática]
retorna um valor NaN tranquila do determinado tipo de ponto flutuante
Original:
returns a quiet NaN value of the given floating-point type
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(função public static membro) [edit]