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nearbyint, nearbyintf, nearbyintl

From cppreference.com
< c‎ | numeric‎ | math
 
 
 
Common mathematical functions
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nearbyint
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Macro constants
 
Defined in header <math.h>
float       nearbyintf( float arg );
(1) (since C99)
double      nearbyint( double arg );
(2) (since C99)
long double nearbyintl( long double arg );
(3) (since C99)
Defined in header <tgmath.h>
#define nearbyint( arg )
(4) (since C99)
1-3) Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode.
4) Type-generic macro: If arg has type long double, nearbyintl is called. Otherwise, if arg has integer type or the type double, nearbyint is called. Otherwise, nearbyintf is called, respectively.

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 nearbyint and rint is that nearbyint never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard floating-point formats, so nearbyint never overflows on its own; however the result may overflow any integer type (including 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 <stdio.h>
#include <math.h>
#include <fenv.h>
 
int main(void)
{
#pragma STDC FENV_ACCESS ON
    fesetround(FE_TONEAREST);
    printf("rounding to nearest:\nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
    printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
    printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
    printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
    printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
    printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));
 
    fesetround(FE_DOWNWARD);
    printf("rounding down: \nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
    printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
    printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
    printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
    printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
    printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));
 
    printf("nearbyint(-0.0) = %+.1f\n", nearbyint(-0.0));
    printf("nearbyint(-Inf) = %+.1f\n", nearbyint(-INFINITY));
}

Output:

rounding to nearest:
nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +4.0
nearbyint(-2.3) = -2.0  nearbyint(-2.5) = -2.0  nearbyint(-3.5) = -4.0
rounding down: 
nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +3.0
nearbyint(-2.3) = -3.0  nearbyint(-2.5) = -3.0  nearbyint(-3.5) = -4.0
nearbyint(-0.0) = -0.0
nearbyint(-Inf) = -inf

[edit] See also

(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)
rounds to an integer using current rounding mode with
exception if the result differs
(function) [edit]
(C99)(C99)(C99)
rounds to nearest integer, rounding away from zero in halfway cases
(function) [edit]
gets or sets rounding direction
(function) [edit]
C++ documentation for nearbyint