std::rint, std::lrint, std::llrint – cppreference.com

std::rint, std::lrint, std::llrint

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C++
 
Numerik-Bibliothek
Gemeinsame mathematischen Funktionen
Floating-Point-Umgebung
Komplexe Zahlen
Numerische Arrays
Pseudo-Zufallszahlen
Compile-time rationale Arithmetik (C++11)
Generische numerische Operationen
Original:
Generic numeric operations
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iota(C++11)
accumulate
inner_product
adjacent_difference
partial_sum
 
Gemeinsame mathematischen Funktionen
Funktionen
Original:
Functions
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Grundlegende Bedienung
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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)
Exponentialfunktionen
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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)
Power-Funktionen
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Power functions
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sqrt
cbrt(C++11)
hypot(C++11)
pow
Trigonometrische und hyperbolische Funktionen
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Trigonometric and hyperbolic functions
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sinh
cosh
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asinh(C++11)
acosh(C++11)
atanh(C++11)
Fehler-und Gamma-Funktionen
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Error and gamma functions
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erf(C++11)
erfc(C++11)
lgamma(C++11)
tgamma(C++11)
Nächste ganze Zahl Fließkomma-Operationen
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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)
Floating-Point-Manipulation Funktionen
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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)
Klassifizierung / Vergleich
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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)
islessequal(C++11)
islessgreater(C++11)
isunordered(C++11)
Makro Konstanten
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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)
 
<tbody> </tbody>
definiert in Header <cmath>
int rint( float arg );
 (seit C++11)
int rint( double arg );
 (seit C++11)
int rint( long double arg );
 (seit C++11)
int rint( Integral arg );
 (seit C++11)
long lrint( float arg );
 (seit C++11)
long lrint( double arg );
 (seit C++11)
long lrint( long double arg );
 (seit C++11)
long lrint( Integral arg );
 (seit C++11)
long long llrint( float arg );
 (seit C++11)
long long llrint( double arg );
 (seit C++11)
long long llrint( long double arg );
 (seit C++11)
long long llrint( Integral arg );
 (seit C++11)
Rundet die Floating-Point-Argument arg auf einen ganzzahligen Wert in Floating-Point-Format, mit dem aktuellen Rundung Modus. Wenn das Ergebnis unterscheidet sich von arg (dh arg war kein ganzzahliger Wert schon), wird die Gleitkomma-Ausnahme FE_INEXACT angehoben .
Original:
Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode. If the result differs from arg (i.e., arg was not an integer value already), the floating-point exception FE_INEXACT is raised.
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Parameter

arg -
Floating-Point-Wert
Original:
floating point value
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Rückgabewert

Das ganzzahlige Ergebnis der Rundung arg
Original:
The integer result of rounding arg
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Notes

Der einzige Unterschied zwischen std::nearbyint und std::rint ist, dass std::rint kann die FE_INEXACT Gleitkomma-Ausnahme zu erhöhen, während std::nearbyint wirft es nie .
Original:
The only difference between std::nearbyint and std::rint is that std::rint may raise the FE_INEXACT floating-point exception, while std::nearbyint never raises it.
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Beispiel

#include <cmath>
#include <cfenv>
#include <iostream>
int main()
{
    #pragma STDC FENV_ACCESS ON
    std::fesetround(FE_DOWNWARD);
    std::cout << "rounding using FE_DOWNWARD:\n" << std::fixed
              << " 12.0 ->  " << std::rint(12.0) << '\n'
              << " 12.1 ->  " << std::rint(12.1) << '\n'
              << "-12.1 -> " << std::rint(-12.1) << '\n'
              << " 12.5 ->  " << std::rint(12.5) << '\n'
              << " 12.9 ->  " << std::rint(12.9) << '\n'
              << "-12.9 -> " << std::rint(-12.9) << '\n'
              << " 13.0 ->  " << std::rint(13.0) << '\n';
    std::fesetround(FE_TONEAREST);
    std::cout << "rounding using FE_TONEAREST: \n"
              << " 12.0 ->  " << std::rint(12.0) << '\n'
              << " 12.1 ->  " << std::rint(12.1) << '\n'
              << "-12.1 -> " << std::rint(-12.1) << '\n'
              << " 12.5 ->  " << std::rint(12.5) << '\n'
              << " 12.9 ->  " << std::rint(12.9) << '\n'
              << "-12.9 -> " << std::rint(-12.9) << '\n'
              << " 13.0 ->  " << std::rint(13.0) << '\n';

    std::cout << "When rounding 12.0 ";
    std::feclearexcept(FE_ALL_EXCEPT);
    std::rint(12.0);
    if(std::fetestexcept(FE_ALL_EXCEPT) & FE_INEXACT) {
        std::cout << "inexact result reported\n";
    } else {
        std::cout << "inexact result not reported\n";
    }

    std::cout << "When rounding 12.1 ";
    std::rint(12.1);
    if(std::fetestexcept(FE_ALL_EXCEPT) & FE_INEXACT) {
        std::cout << "inexact result reported\n";
    } else {
        std::cout << "inexact result not reported\n";
    }
}

Output: 

rounding using FE_DOWNWARD:
 12.0 ->  12.000000
 12.1 ->  12.000000
-12.1 -> -13.000000
 12.5 ->  12.000000
 12.9 ->  12.000000
-12.9 -> -13.000000
 13.0 ->  13.000000
rounding using FE_TONEAREST: 
 12.0 ->  12.000000
 12.1 ->  12.000000
-12.1 -> -12.000000
 12.5 ->  12.000000
 12.9 ->  13.000000
-12.9 -> -13.000000
 13.0 ->  13.000000
When rounding 12.0 inexact result not reported
When rounding 12.1 inexact result reported

Siehe auch