nearbyintf (3)  Linux Manuals
nearbyintf: round
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);
Link with lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
nearbyint(), nearbyintf(), nearbyintl():
 _POSIX_C_SOURCE >= 200112L  _ISOC99_SOURCE
rint():

_ISOC99_SOURCE  _POSIX_C_SOURCE >= 200112L
 _XOPEN_SOURCE >= 500
 /* Since glibc 2.19: */ _DEFAULT_SOURCE
 /* Glibc versions <= 2.19: */ _BSD_SOURCE  _SVID_SOURCE
rintf(), rintl():

_ISOC99_SOURCE  _POSIX_C_SOURCE >= 200112L
 /* Since glibc 2.19: */ _DEFAULT_SOURCE
 /* Glibc versions <= 2.19: */ _BSD_SOURCE  _SVID_SOURCE
DESCRIPTION
The nearbyint(), nearbyintf(), and nearbyintl() functions round their argument to an integer value in floatingpoint format, using the current rounding direction (see fesetround(3)) and without raising the inexact exception. When the current rounding direction is to nearest, these functions round halfway cases to the even integer in accordance with IEEE754.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.12001 documents a range error for overflows, but see NOTES.ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).Interface  Attribute  Value 
nearbyint(),
nearbyintf(),
nearbyintl(), rint(), rintf(), rintl()  Thread safety  MTSafe 
CONFORMING TO
C99, POSIX.12001, POSIX.12008.NOTES
SUSv2 and POSIX.12001 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 errorhandling 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 IEEE754 standard 32bit and 64bit floatingpoint 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.
COLOPHON
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