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std::logb

提供: cppreference.com
< cpp‎ | numeric‎ | math

 
 
ニューメリックスライブラリ
一般的な数学関数
浮動小数点環境
複素数
数値配列
擬似乱数生成
コンパイル時有理数演算 (C++11)
汎用の数値演算
Original:
Generic numeric operations
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iota(C++11)
accumulate
inner_product
adjacent_difference
partial_sum
 
一般的な数学関数
機能します
Original:
Functions
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基本操作
Original:
Basic operations
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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)
指数関数
Original:
Exponential functions
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exp
exp2(C++11)
expm1(C++11)
log
log10
log1p(C++11)
log2(C++11)
電源機能
Original:
Power functions
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sqrt
cbrt(C++11)
hypot(C++11)
pow
三角関数や双曲線関数
Original:
Trigonometric and hyperbolic functions
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sinh
cosh
tanh
asinh(C++11)
acosh(C++11)
atanh(C++11)
エラーおよびガンマ関数
Original:
Error and gamma functions
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erf(C++11)
erfc(C++11)
lgamma(C++11)
tgamma(C++11)
最も近い整数の浮動小数点演算
Original:
Nearest integer floating point operations
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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)
点操作関数に浮かぶ
Original:
Floating point manipulation functions
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ldexp
scalbn
scalbln
(C++11)
(C++11)
ilogb(C++11)
logb(C++11)
frexp
modf
nextafter
nexttoward
(C++11)
(C++11)
copysign(C++11)
分類/比較
Original:
Classification/Comparison
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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)
マクロ定数
Original:
Macro constants
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FP_NORMAL
FP_SUBNORMAL
FP_ZERO
FP_INFINITE
FP_NAN
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
 
Defined in header <cmath>
float       logb( float arg );
(C + + 11以来)
double      logb( double arg );
(C + + 11以来)
long double logb( long double arg );
(C + + 11以来)
double      logb( Integral arg );
(C + + 11以来)
浮動小数点引数argから指数の値を抽出し、浮動小数点値として返します。正式には、結果が符号付き浮動小数点値としてlog
r
|arg|
の不可欠な部分であり、非ゼロの引数のため、どこrですstd::numeic_limits<T>::radixTargの浮動小数点型である。 argが非正規の場合は、それが標準化したかのように扱われます.
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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目次

[編集] パラメータ

arg -
浮動小数点値
Original:
floating point value
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[編集] 値を返します

浮動小数点の指数.
Original:
The floating-point exponent.
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argがゼロの場合は領域エラーまたは範囲エラーが発生することがあります.
Original:
Domain or range error may occur if arg is zero.
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[編集] ノート

std::logbによって返さ指数std::frexpため、e、1〜std::logb(通常|arg*r-e
|
r)、しかしのために:1によって返される指数の値は、常に異なるため、正規化要件の2によって再び調整指数が1未満である指数部がestd::frexpによって返さ|arg*2-e
|
です0.51.
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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[編集]

異なる浮動小数点分解機能を比較します
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

[編集] も参照してください

数値は仮数と2の力に分解する
Original:
decomposes a number into significand and a power of 2
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(機能) [edit]
(C++11)
数値の指数を抽出します
Original:
extracts exponent of the number
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(機能) [edit]
(C++11)
(C++11)
累乗しFLT_RADIXによって数を乗算します
Original:
multiplies a number by FLT_RADIX raised to a power
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(機能) [edit]