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    std::logb

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    C++
     
    Numerik-Bibliothek
    Gemeinsame mathematischen Funktionen
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    (C++11)
    ilogb(C++11)
    logb(C++11)
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    definiert in Header <cmath>
    float       logb(float arg );
    		(seit C++11)
    double      logb(double arg );
    		(seit C++11)
    longdouble logb(longdouble arg );
    		(seit C++11)
    double      logb( Integral arg );
    		(seit C++11)
    Extrahiert den Wert des Exponenten aus der Floating-Point-Argument arg und gibt es als Floating-Point-Wert. Formal ist das Ergebnis der integraler Bestandteil des log
    r    |arg|     als vorzeichenbehaftete Fließkommazahl, für Nicht-Null arg, wo r ist std::numeic_limits<T>::radix und T ist der Floating-Point-Typ arg. Wenn arg subnormale ist, wird behandelt, als ob es wurde normalisiert .
    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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    Inhaltsverzeichnis

    [Bearbeiten]Parameter

    arg -
    Floating-Point-Wert
    Original:
    floating point value
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    [Bearbeiten]Rückgabewert

    Die Floating-Point-Exponenten .
    Original:
    The floating-point exponent.
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    Domain oder den Bereich Fehler kann auftreten, wenn arg Null ist .
    Original:
    Domain or range error may occur if arg is zero.
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    [Bearbeiten]Notes

    Der Wert des Exponenten zurückschickt std::logb immer 1 kleiner als der Exponent durch std::frexp wegen der unterschiedlichen Anforderungen Normalisierung retuned: für den Exponenten e durch std::logb zurückgekehrt ist |arg*r-e
    |     zwischen 1 und r (typischerweise zwischen 1 und 2), aber für die Exponenten e durch std::frexp zurückgegeben wird, ist |arg*2-e
    |     zwischen 0.5 und 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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    [Bearbeiten]Beispiel

    Vergleicht verschiedene Floating-Point-Zersetzung Funktionen
    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

    [Bearbeiten]Siehe auch

    zersetzt eine Zahl in Mantisse und einer Leistung von 2
    Original:
    decomposes a number into significand and a power of 2
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    (Funktion)[edit]
    (C++11)
    extrahiert Exponent der Zahl
    Original:
    extracts exponent of the number
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    (Funktion)[edit]
    (C++11)
    (C++11)
    multipliziert eine Zahl durch FLT_RADIX potenziert
    Original:
    multiplies a number by FLT_RADIX raised to a power
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    (Funktion)[edit]
    Von „https://de.cppreference.com/mwiki/index.php?title=cpp/numeric/math/logb&oldid=29606“
    close