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std::ilogb

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< cpp‎ | numeric‎ | math

 
 
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Defined in header <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.

Contenido

[editar] Parámetros

arg -
flotando valor en puntos
Original:
floating point value
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[editar] Valor de retorno

The floating-point exponent, cast to integer, as if by static_cast<int>(std::logb(arg)).

Error de dominio o rango puede producirse si arg es cero, se devuelve FP_ILOGB0 en ese caso .
Original:
Domain or range error may occur if arg is zero, FP_ILOGB0 is returned in that case.
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Error de dominio o rango puede producirse si arg es infinito, MAX_INT se devuelve en ese caso .
Original:
Domain or range error may occur if arg is infinite, MAX_INT is returned in that case.
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Error de dominio o rango puede ocurrir si arg es NaN, se devuelve FP_ILOGBNAN en ese caso .
Original:
Domain or range error may occur if arg is NaN, FP_ILOGBNAN is returned in that case.
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Si el resultado no se puede representar como int, el resultado es indefinido .
Original:
If the result cannot be represented as int, the result is undefined.
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[editar] Notas

El valor del exponente devuelto por std::ilogb siempre es 1 menos que el exponente reajustada por std::frexp debido a los requisitos de normalización diferentes: para la e exponente devuelto por std::ilogb, |arg*r-e
|
es entre 1 y r (típicamente entre 1 y 2), pero para la exponente e devuelto por std::frexp, |arg*2-e
|
es entre 0.5 y 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 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] Ejemplo

Compara las diferentes funciones de punto flotante de descomposición
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';
}

Output:

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] Ver también

se descompone un número en mantisa y una potencia de 2
Original:
decomposes a number into significand and a power of 2
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(función) [edit]
(C++11)
extrae exponente de la serie
Original:
extracts exponent of the number
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(función) [edit]
(C++11)
(C++11)
multiplica un número por FLT_RADIX elevado a una potencia
Original:
multiplies a number by FLT_RADIX raised to a power
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(función) [edit]