std::ilogb
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| Definido no cabeçalho <cmath>
|
||
| int ilogb( float arg ); |
(desde C++11) | |
| int ilogb( double arg ); |
(desde C++11) | |
| int ilogb( long double arg ); |
(desde C++11) | |
| double ilogb( Integral arg ); |
(desde C++11) | |
| #define FP_ILOGB0 /*implementation-defined*/ |
(desde C++11) | |
| #define FP_ILOGBNAN /*implementation-defined*/ |
(desde C++11) | |
Extracts the value of the exponent from the floating-point argument arg, and returns it as a signed integer value. Formally, the result is the integral part of log
r|arg| as a signed integral value, for non-zero arg, where r is std::numeric_limits<T>::radix and T is the floating-point type of arg.
Índice |
[editar] Parâmetros
| arg | - | flutuando valor de ponto
Original: floating point value The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
[editar] Valor de retorno
The floating-point exponent, cast to integer, as if by static_cast<int>(std::logb(arg)).
Erro domínio ou intervalo pode ocorrer se
arg é zero, FP_ILOGB0 é retornado, nesse caso,.Original:
Domain or range error may occur if
arg is zero, FP_ILOGB0 is returned in that case.The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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Erro de domínio ou intervalo pode ocorrer se
arg é infinito, MAX_INT é devolvido em caso.Original:
Domain or range error may occur if
arg is infinite, MAX_INT is returned in that case.The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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Erro de domínio ou intervalo pode ocorrer se
arg é NaN, FP_ILOGBNAN é devolvido em caso.Original:
Domain or range error may occur if
arg is NaN, FP_ILOGBNAN is returned in that case.The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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Se o resultado não pode ser representado como int, o resultado é indefinido.
Original:
If the result cannot be represented as int, the result is undefined.
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[editar] Notas
O valor do expoente retornado por std::ilogb é sempre 1 a menos do que o expoente retuned std::frexp por causa das exigências de normalização diferentes: para o expoente
| está entre 1 e
| é entre 0.5 e 1.
e retornado por std::ilogb, |arg*r-e| está entre 1 e
r (tipicamente entre 1 e 2), mas para o expoente e retornado por std::frexp, |arg*2-e| é entre 0.5 e 1.
Original:
The value of the exponent returned by std::ilogb is always 1 less than the exponent retuned by std::frexp because of the different normalization requirements: for the exponent
| is between 1 and
| is between 0.5 and 1.
e returned by std::ilogb, |arg*r-e| is between 1 and
r (typically between 1 and 2), but for the exponent e returned by std::frexp, |arg*2-e| is between 0.5 and 1.
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[editar] Exemplo
Compara diferentes funções de ponto flutuante de decomposição
Original:
Compares different floating-point decomposition functions
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#include <iostream> #include <cmath> #include <limits> int main() { double f = 123.45; std::cout << "Given the number " << f << " or " << std::hexfloat << f << std::defaultfloat << " in hex,\n"; double f3; double f2 = std::modf(f, &f3); std::cout << "modf() makes " << f3 << " + " << f2 << '\n'; int i; f2 = std::frexp(f, &i); std::cout << "frexp() makes " << f2 << " * 2^" << i << '\n'; i = std::ilogb(f); std::cout << "logb()/ilogb() make " << f/std::scalbn(1.0, i) << " * " << std::numeric_limits<double>::radix << "^" << std::ilogb(f) << '\n'; }
Saída:
Given the number 123.45 or 0x1.edccccccccccdp+6 in hex, modf() makes 123 + 0.45 frexp() makes 0.964453 * 2^7 logb()/ilogb() make 1.92891 * 2^6
[editar] Veja também
| decompõe um número em significand e um poder de 2 Original: decomposes a number into significand and a power of 2 The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (função) | |
| (C++11) |
extrai expoente do número Original: extracts exponent of the number The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (função) |
| (C++11) (C++11) |
multiplica um número por FLT_RADIX elevado a uma potência Original: multiplies a number by FLT_RADIX raised to a power The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (função) |
