Linux manual pages Section 3: Subroutines  

Name

nearbyint, nearbyintf, nearbyintl, rint, rintf, rintl — round to nearest integer

Synopsis

#include <math.h>
double nearbyint( double x);
 
float nearbyintf( float x);
 
long double nearbyintl( long double x);
 
double rint( double x);
 
float rintf( float x);
 
long double rintl( long double x);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
nearbyint(), nearbyintf(), nearbyintl():
_XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L || _ISOC99_SOURCE;
or cc -std=c99
rint():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
rintf(), rintl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
[Note] Note

Link with −lm.

DESCRIPTION

The nearbyint(), nearbyintf(), and nearbyintl() functions round their argument to an integer value in floating-point format, using the current rounding direction (see fesetround(3)) and without raising the inexact exception.

The rint(), rintf(), and rintl() functions do the same, but will raise the inexact exception (FE_INEXACT, checkable via fetestexcept(3)) when the result differs in value from the argument.

RETURN VALUE

These functions return the rounded integer value.

If x is integral, +0, −0, NaN, or infinite, x itself is returned.

ERRORS

No errors occur. POSIX.1-2001 documents a range error for overflows, but see NOTES.

ATTRIBUTES

Multithreading (see pthreads(7))

The nearbyint(), nearbyintf(), nearbyintl(), rint(), rintf(), and rintl() functions are thread-safe.

CONFORMING TO

C99, POSIX.1-2001.

NOTES

SUSv2 and POSIX.1-2001 contain text about overflow (which might set errno to ERANGE, or raise an FE_OVERFLOW exception). In practice, the result cannot overflow on any current machine, so this error-handling stuff is just nonsense. (More precisely, overflow can happen only when the maximum value of the exponent is smaller than the number of mantissa bits. For the IEEE-754 standard 32-bit and 64-bit floating-point numbers the maximum value of the exponent is 128 (respectively, 1024), and the number of mantissa bits is 24 (respectively, 53).)

If you want to store the rounded value in an integer type, you probably want to use one of the functions described in lrint(3) instead.

SEE ALSO

ceil(3), floor(3), lrint(3), round(3), trunc(3)

COLOPHON

This page is part of release 3.54 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man−pages/.


  Copyright 2001 Andries Brouwer <aebcwi.nl>.
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
    <mtk.manpagesgmail.com>

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