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std::logb

De cppreference.com
< cpp‎ | numeric‎ | math

 
 
Bibliothèque Numerics
Fonctions mathématiques courantes
Virgule flottante environnement
Nombres complexes
Tableaux numériques
La génération de nombres pseudo-aléatoires
Moment de la compilation arithmétique rationnelle (C++11)
Génériques des opérations numériques
Original:
Generic numeric operations
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iota (C++11)
accumulate
inner_product
adjacent_difference
partial_sum
 
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{{{1}}}
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{{{2}}}
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Fonctions
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Functions
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Opérations de base
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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)
Les fonctions exponentielles
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Exponential functions
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exp
exp2 (C++11)
expm1 (C++11)
log
log10
log1p (C++11)
log2 (C++11)
Les fonctions de puissance
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Power functions
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sqrt
cbrt (C++11)
hypot (C++11)
pow
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Trigonometric and hyperbolic functions
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{{{1}}}
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{{{2}}}
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Erreur fonctions et gamma
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Error and gamma functions
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erf (C++11)
erfc (C++11)
lgamma (C++11)
tgamma (C++11)
Entier le plus proche opérations en virgule flottante
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Nearest integer floating point operations
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floor
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Flottant fonctions de manipulation de points
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Floating point manipulation functions
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ldexp
scalbn
scalbln
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(C++11)
ilogb (C++11)
logb (C++11)
frexp
modf
nextafter
nexttoward
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copysign (C++11)
Classification / Comparaison
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Classification/Comparison
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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)
Macro constantes
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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)
</div>
 
</div>
Defined in header <cmath>
float       logb( float arg );
(depuis C++11)
double      logb( double arg );
(depuis C++11)
long double logb( long double arg );
(depuis C++11)
double      logb( Integral arg );
(depuis C++11)
Extrait la valeur de l'exposant de la arg argument en virgule flottante, et retourne une valeur à virgule flottante. Formellement, le résultat est la partie intégrante de log
r
|arg|
signé en tant que valeur à virgule flottante, pour les non-nul arg, où r est std::numeic_limits<T>::radix et T est le type à virgule flottante de arg. Si arg est inférieure à la normale, elle est traitée comme si elle était normalisée .
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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Sommaire

[modifier] Paramètres

arg -
valeur du point flottant
Original:
floating point value
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[modifier] Retourne la valeur

L'exposant virgule flottante .
Original:
The floating-point exponent.
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Erreur de domaine ou une plage peut se produire si arg est nul .
Original:
Domain or range error may occur if arg is zero.
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[modifier] Notes

La valeur de l'exposant retourné par std::logb est toujours inférieur de 1 l'exposant retuned par std::frexp en raison des exigences de normalisation différents: pour le e exposant retourné par std::logb, |arg*r-e
|
est comprise entre 1 et r (typiquement entre 1 et 2), mais pour le exposant e retourné par std::frexp, |arg*2-e
|
se situe entre 0.5 et 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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[modifier] Exemple

Compare les différentes fonctions de décomposition en virgule flottante
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';
}

Résultat :

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

[modifier] Voir aussi

se décompose en un certain nombre mantisse et d'une puissance de 2
Original:
decomposes a number into significand and a power of 2
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(fonction) [edit]
(C++11)
extrait exposant du nombre
Original:
extracts exponent of the number
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(fonction) [edit]
(C++11)
(C++11)
multiplie par un nombre FLT_RADIX élevé à une puissance
Original:
multiplies a number by FLT_RADIX raised to a power
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(fonction) [edit]