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RINT(3) Library Functions Manual RINT(3)

nearbyint, nearbyintf, nearbyintl, rint, rintf, rintl
round to integral value in floating-point format

#include <math.h>
nearbyint(double x);
nearbyintf(float x);
long double
nearbyintl(long double x);
rint(double x);
rintf(float x);
long double
rintl(long double x);

The rint(), rintf(), and rintl() functions return the integral value nearest to x according to the prevailing rounding mode.
The nearbyint(), nearbyintf(), and nearbyintl() functions do the same, but without raising the “inexact” floating-point exception.

abs(3), ceil(3), fabs(3), floor(3)

A rint() function appeared in Version 6 AT&T UNIX.
June 5, 2013 OpenBSD-current