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std::nearbyint, std::nearbyintf, std::nearbyintl

From natekohl.net
< cpp‎ | numeric‎ | math
 
 
 
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nearbyint
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Defined in header <cmath>
float       nearbyint ( float arg );
float       nearbyintf( float arg );
(1) (since C++11)
double      nearbyint ( double arg );
(2) (since C++11)
long double nearbyint ( long double arg );
long double nearbyintl( long double arg );
(3) (since C++11)
double      nearbyint ( IntegralType arg );
(4) (since C++11)
1-3) Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode.
4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to (2) (the argument is cast to double).

Contents

[edit] Parameters

arg - floating point value

[edit] Return value

The nearest integer value to arg, according to the current rounding mode, is returned.

[edit] Error handling

This function is not subject to any of the errors specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

  • FE_INEXACT is never raised
  • If arg is ±∞, it is returned, unmodified
  • If arg is ±0, it is returned, unmodified
  • If arg is NaN, NaN is returned

[edit] Notes

The only difference between std::nearbyint and std::rint is that std::nearbyint never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard floating-point formats, so std::nearbyint never overflows on its own; however the result may overflow any integer type (including std::intmax_t), when stored in an integer variable.

If the current rounding mode is FE_TONEAREST, this function rounds to even in halfway cases (like rint, but unlike round).

[edit] Example

#include <iostream>
#include <cmath>
#include <cfenv>
 
int main()
{
#pragma STDC FENV_ACCESS ON
    std::fesetround(FE_TONEAREST);
    std::cout << "rounding to nearest: \n"
              << "nearbyint(+2.3) = " << std::nearbyint(2.3)
              << "  nearbyint(+2.5) = " << std::nearbyint(2.5)
              << "  nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
              << "nearbyint(-2.3) = " << std::nearbyint(-2.3)
              << "  nearbyint(-2.5) = " << std::nearbyint(-2.5)
              << "  nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';
 
    std::fesetround(FE_DOWNWARD);
    std::cout << "rounding down:\n"
              << "nearbyint(+2.3) = " << std::nearbyint(2.3)
              << "  nearbyint(+2.5) = " << std::nearbyint(2.5)
              << "  nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
              << "nearbyint(-2.3) = " << std::nearbyint(-2.3)
              << "  nearbyint(-2.5) = " << std::nearbyint(-2.5)
              << "  nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';
 
    std::cout << "nearbyint(-0.0) = " << std::nearbyint(-0.0)  << '\n'
              << "nearbyint(-Inf) = " << std::nearbyint(-INFINITY) << '\n';
}

Output:

rounding to nearest: 
nearbyint(+2.3) = 2  nearbyint(+2.5) = 2  nearbyint(+3.5) = 4
nearbyint(-2.3) = -2  nearbyint(-2.5) = -2  nearbyint(-3.5) = -4
rounding down:
nearbyint(+2.3) = 2  nearbyint(+2.5) = 2  nearbyint(+3.5) = 3
nearbyint(-2.3) = -3  nearbyint(-2.5) = -3  nearbyint(-3.5) = -4
nearbyint(-0.0) = -0
nearbyint(-Inf) = -inf

[edit] See also

(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)
nearest integer using current rounding mode with
exception if the result differs
(function) [edit]
(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)
nearest integer, rounding away from zero in halfway cases
(function) [edit]
(C++11)(C++11)
gets or sets rounding direction
(function) [edit]
C documentation for nearbyint