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Nearbyint

Defined in header <cmath>.

Description

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 num  (od C++23).

Additional Overloads are provided for all integer types, which are treated as double.

Declarations

// 1)
/* floating-point-type */ nearbyint( /* floating-point-type */ num );
// 2)
float nearbyintf( float num );
// 3)
long double nearbyintl( long double num );
Additional Overloads
// 4)
template< class Integer >
double nearbyint ( Integer num );

Parameters

num - floating-point or integer value

Return value

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

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

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 Additional Overloads.

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)).

Examples

#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) << '\n'
<< "nearbyint(+2.5) = "
<< std::nearbyint(2.5) << '\n'
<< "nearbyint(+3.5) = "
<< std::nearbyint(3.5) << '\n'
<< "nearbyint(-2.3) = "
<< std::nearbyint(-2.3) << '\n'
<< "nearbyint(-2.5) = "
<< std::nearbyint(-2.5) << '\n'
<< "nearbyint(-3.5) = "
<< std::nearbyint(-3.5) << '\n\n';

std::fesetround(FE_DOWNWARD);
std::cout
<< "rounding down:\n"

<< "nearbyint(+2.3) = "
<< std::nearbyint(2.3) << '\n'
<< "nearbyint(+2.5) = "
<< std::nearbyint(2.5) << '\n'
<< "nearbyint(+3.5) = "
< std::nearbyint(3.5) << '\n'
<< "nearbyint(-2.3) = "
<< std::nearbyint(-2.3) << '\n'
<< "nearbyint(-2.5) = "
<< std::nearbyint(-2.5) << '\n'
<< "nearbyint(-3.5) = "
<< std::nearbyint(-3.5) << '\n';

std::cout
<< "nearbyint(-0.0) = "
<< std::nearbyint(-0.0) << '\n'
<< "nearbyint(-Inf) = "
<< std::nearbyint(-INFINITY) << '\n';
}

Result
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

Nearbyint

Defined in header <cmath>.

Description

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 num  (od C++23).

Additional Overloads are provided for all integer types, which are treated as double.

Declarations

// 1)
/* floating-point-type */ nearbyint( /* floating-point-type */ num );
// 2)
float nearbyintf( float num );
// 3)
long double nearbyintl( long double num );
Additional Overloads
// 4)
template< class Integer >
double nearbyint ( Integer num );

Parameters

num - floating-point or integer value

Return value

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

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

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 Additional Overloads.

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)).

Examples

#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) << '\n'
<< "nearbyint(+2.5) = "
<< std::nearbyint(2.5) << '\n'
<< "nearbyint(+3.5) = "
<< std::nearbyint(3.5) << '\n'
<< "nearbyint(-2.3) = "
<< std::nearbyint(-2.3) << '\n'
<< "nearbyint(-2.5) = "
<< std::nearbyint(-2.5) << '\n'
<< "nearbyint(-3.5) = "
<< std::nearbyint(-3.5) << '\n\n';

std::fesetround(FE_DOWNWARD);
std::cout
<< "rounding down:\n"

<< "nearbyint(+2.3) = "
<< std::nearbyint(2.3) << '\n'
<< "nearbyint(+2.5) = "
<< std::nearbyint(2.5) << '\n'
<< "nearbyint(+3.5) = "
< std::nearbyint(3.5) << '\n'
<< "nearbyint(-2.3) = "
<< std::nearbyint(-2.3) << '\n'
<< "nearbyint(-2.5) = "
<< std::nearbyint(-2.5) << '\n'
<< "nearbyint(-3.5) = "
<< std::nearbyint(-3.5) << '\n';

std::cout
<< "nearbyint(-0.0) = "
<< std::nearbyint(-0.0) << '\n'
<< "nearbyint(-Inf) = "
<< std::nearbyint(-INFINITY) << '\n';
}

Result
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