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

From cppreference.com
< cpp‎ | numeric‎ | math
 
 
 
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nearbyint
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Defined in header <cmath>
(1)
float       nearbyint ( float num );

double      nearbyint ( double num );

long double nearbyint ( long double num );
(until C++23)
/* floating-point-type */
            nearbyint ( /* floating-point-type */ num );
(since C++23)
float       nearbyintf( float num );
(2) (since C++11)
long double nearbyintl( long double num );
(3) (since C++11)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer >
double      nearbyint ( Integer num );
(A)
1-3) Rounds the floating-point argument num to an integer value in floating-point format, using the current rounding mode. The library provides overloads of std::nearbyint for all cv-unqualified floating-point types as the type of the parameter.(since C++23)
A) Additional overloads are provided for all integer types, which are treated as double.
(since C++11)

Contents

[edit] Parameters

num - floating-point or integer value

[edit] Return value

The nearest integer value to num, 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 num is ±∞, it is returned, unmodified.
  • If num is ±0, it is returned, unmodified.
  • If num 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 std::rint, but unlike std::round).

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::nearbyint(num) has the same effect as std::nearbyint(static_cast<double>(num)).

[edit] Example

#include <cfenv>
#include <cmath>
#include <iostream>
#pragma STDC FENV_ACCESS ON
 
int main()
{
    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