Namespace
Varianti

std::ilogb

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< cpp‎ | numeric‎ | math

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C++
 
Numeri libreria
Comuni funzioni matematiche
Virgola mobile ambiente
I numeri complessi
Array numerici
Pseudo-casuale generazione
In fase di compilazione aritmetica razionale (C++11)
Generici operazioni numeriche
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Generic numeric operations
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iota(C++11)
accumulate
inner_product
adjacent_difference
partial_sum
 
Comuni funzioni matematiche
Funzioni
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Functions
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Operazioni di 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)
Funzioni esponenziali
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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)
Funzioni di risparmio energia
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Power functions
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sqrt
cbrt(C++11)
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Trigonometric and hyperbolic functions
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sinh
cosh
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asinh(C++11)
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Errore e gamma funzioni
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Error and gamma functions
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erf(C++11)
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tgamma(C++11)
Più vicini operazioni di interi in virgola mobile
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Nearest integer floating point operations
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ceil
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llrint		(C++11)
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Floating funzioni di manipolazione di punti
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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)
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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)
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Macro costanti
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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)
 
Elemento definito nell'header <cmath>
int         ilogb( float arg );
 (dal C++11)
int         ilogb( double arg );
 (dal C++11)
int         ilogb( long double arg );
 (dal C++11)
double      ilogb( Integral arg );
 (dal C++11)
#define FP_ILOGB0 /*implementation-defined*/
 (dal C++11)
#define FP_ILOGBNAN /*implementation-defined*/
 (dal C++11)

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.

Indice

[modifica] Parametri

arg -
valore in virgola mobile
Original:
floating point value
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[modifica] Valore di ritorno

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

Errore di dominio o l'intervallo si può verificare se arg è pari a zero, FP_ILOGB0 viene restituito in questo caso.
Original:
Domain or range error may occur if arg is zero, FP_ILOGB0 is returned in that case.
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Errore di dominio o l'intervallo si può verificare se arg è infinito, MAX_INT viene restituito in questo caso.
Original:
Domain or range error may occur if arg is infinite, MAX_INT is returned in that case.
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Errore di dominio o l'intervallo si può verificare se arg è NaN, FP_ILOGBNAN viene restituito in questo caso.
Original:
Domain or range error may occur if arg is NaN, FP_ILOGBNAN is returned in that case.
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Se il risultato non può essere rappresentato come int, il risultato è indefinito.
Original:
If the result cannot be represented as int, the result is undefined.
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[modifica] Note

Il valore dell'esponente restituito da std::ilogb è sempre inferiore a 1 l'esponente rientrati da std::frexp causa dei diversi requisiti di normalizzazione: per l'esponente e restituito da std::ilogb, |arg*r-e
| è tra 1 e r (tipicamente tra 1 e 2), ma per l' esponente e restituito da std::frexp, |arg*2-e
| è tra 0.5 e 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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[modifica] Esempio

Confronta diversi virgola mobile funzioni di decomposizione
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

[modifica] Vedi anche
scompone un numero in significante e una potenza di 2
Original:
decomposes a number into significand and a power of 2
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(funzione) [modifica]
(C++11)
estrae esponente del numero
Original:
extracts exponent of the number
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(funzione) [modifica]
(C++11)
(C++11)
moltiplica un numero per FLT_RADIX elevato a una potenza
Original:
multiplies a number by FLT_RADIX raised to a power
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(funzione) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/numeric/math/ilogb&oldid=26281"