std::logb

 

C++

Язык

Понятия (концепции)

Утилиты

Строки

Контейнеры

Алгоритмы

Итераторы

Работа с числами

Ввод / вывод

Локализация

Регулярные выражения (C++11)

Атомарные примитивы (C++11)

Потоки (C++11)

 

Numerics библиотеки

Общие математические функции

Плавающей точкой окружающей среды

Комплексные числа

Числовых массивов

Псевдослучайных чисел поколения

Во время компиляции рациональной арифметики (C++11)

Generic числовые операции Original: Generic numeric operations The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

iota (C++11)

accumulate

inner_product

adjacent_difference

partial_sum

 

Общие математические функции

Функции Original: Functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
Основные операции Original: Basic operations The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
abs(int) labs llabs imaxabs (C++11) abs(float) fabs div ldiv lldiv imaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nan nanf nanl (C++11) (C++11) (C++11)
Экспоненциальной функции Original: Exponential functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
exp exp2 (C++11) expm1 (C++11)	log log10 log1p (C++11) log2 (C++11)
Мощность функций Original: Power functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
sqrt cbrt (C++11)	hypot (C++11) pow
Тригонометрические и гиперболические функции Original: Trigonometric and hyperbolic functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11)

Ошибка и гамма-функции Original: Error and gamma functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
Ближайшее целое число операций с плавающей точкой Original: Nearest integer floating point operations The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
ceil floor round lround llround (C++11) (C++11) (C++11)	trunc (C++11) nearbyint (C++11) rint lrint llrint (C++11) (C++11) (C++11)
Плавающей точкой функции манипуляции Original: Floating point manipulation functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
ldexp scalbn scalbln (C++11) (C++11) ilogb (C++11) logb (C++11)	frexp modf nextafter nexttoward (C++11) (C++11) copysign (C++11)
Классификация / сравнения Original: Classification/Comparison The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
Макро констант Original: Macro constants The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
HUGE_VALF HUGE_VAL HUGE_VALL (C++11) (C++11) INFINITY (C++11) NAN (C++11) math_errhandling MATH_ERRNO MATH_ERREXCEPT (C++11)	FP_NORMAL FP_SUBNORMAL FP_ZERO FP_INFINITE FP_NAN (C++11) (C++11) (C++11) (C++11) (C++11)

 

Заголовочный файл <cmath>
float       logb( float arg );		(начиная с C++11)
double      logb( double arg );		(начиная с C++11)
long double logb( long double arg );		(начиная с C++11)
double      logb( Integral arg );		(начиная с C++11)

Извлекает значение показателя с плавающей точкой arg аргумент, и возвращает его как значение с плавающей точкой. Формально, результатом является неотъемлемой частью log
r|arg| как подписанное значение с плавающей точкой, для ненулевых аг, где r является std::numeic_limits<T>::radix и T является плавающей точкой типа arg. Если arg субнормальна, он рассматривается как если бы она была нормализована.

Original:

Extracts the value of the exponent from the floating-point argument arg, and returns it as a floating-point value. Formally, the result is the integral part of log
r|arg| as a signed floating-point value, for non-zero arg, where r is std::numeic_limits<T>::radix and T is the floating-point type of arg. If arg is subnormal, it is treated as though it was normalized.

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Параметры

arg

-

плавающей точкой 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.

Возвращаемое значение

Плавающей точкой показателем.

Original:

The floating-point exponent.

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Домена или диапазона ошибка может возникнуть, если arg равна нулю.

Original:

Domain or range error may occur if arg is zero.

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Notes

Значение показателя возвращается std::logb всегда равен 1 меньше показателя настраивали на std::frexp из-за различных требований нормализации: для показателя e возвращается std::logb, |arg*r-e
| находится между 1 и r (обычно между 1 и 2), но для экспоненты e возвращается std::frexp, |arg*2-e
| между 0.5 и 1.

Original:

The value of the exponent returned by std::logb is always 1 less than the exponent retuned by std::frexp because of the different normalization requirements: for the exponent e returned by std::logb, |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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Пример

Сравнивает различные функции с плавающей точкой разложения

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';
}

Вывод:

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

См. также

frexp	разлагается число в значащей и мощностью 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. (функция)
ilogb (C++11)	извлекает показатель числа 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. (функция)
scalbn scalbln (C++11) (C++11)	число умножается на FLT_RADIX, возведенное в степень 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. (функция)