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std::ilogb

提供: cppreference.com
< cpp‎ | numeric‎ | math

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C++
 
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
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Generic numeric operations
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Exponential functions
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Floating point manipulation functions
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ldexp
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ilogb(C++11)
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Defined in header <cmath>
int         ilogb( float arg );
 (C++11およびそれ以降)
int         ilogb( double arg );
 (C++11およびそれ以降)
int         ilogb( long double arg );
 (C++11およびそれ以降)
double      ilogb( Integral arg );
 (C++11およびそれ以降)
#define FP_ILOGB0 /*implementation-defined*/
 (C++11およびそれ以降)
#define FP_ILOGBNAN /*implementation-defined*/
 (C++11およびそれ以降)

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.

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

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

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可能性があり、FP_ILOGB0はその場合に返されます.
Original:
Domain or range error may occur if arg is zero, FP_ILOGB0 is returned in that case.
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argが無限大である場合、ドメインエラーまたは範囲エラーが発生する可能性があり、MAX_INTはその場合に返されます.
Original:
Domain or range error may occur if arg is infinite, MAX_INT is returned in that case.
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argがNaNの場合は領域エラーまたは範囲エラーが発生する可能性があり、FP_ILOGBNANはその場合に返されます.
Original:
Domain or range error may occur if arg is NaN, FP_ILOGBNAN is returned in that case.
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結果はintとして表すことができない場合、結果は未定義です.
Original:
If the result cannot be represented as int, the result is undefined.
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[編集] ノート

std::ilogbによって返さ指数std::frexpため、e、1〜std::ilogb（通常|arg*r-e
|間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0.5間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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[編集] 例

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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このコードを実行します
#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';
}

出力: 

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] 参照
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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(関数) [edit]
(C++11)
数値の指数を抽出します
Original:
extracts exponent of the number
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(関数) [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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(関数) [edit]
「http://ja.cppreference.com/mwiki/index.php?title=cpp/numeric/math/ilogb&oldid=29839」から取得