NAME

rint, rintf, rintl — round-to-nearest integral value

SYNOPSIS

#include <math.h>

double rint(double x);
float rintf(float x);
long double rintl(long double x);


DESCRIPTION

^[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard.

These functions shall return the integral value (represented as a double) nearest x in the direction of the current rounding mode. The current rounding mode is implementation-defined.

If the current rounding mode rounds toward negative infinity, then rint() shall be equivalent to floor. If the current rounding mode rounds toward positive infinity, then rint() shall be equivalent to ceil. If the current rounding mode rounds towards zero, then rint() shall be equivalent to trunc. ^[MX]  If the current rounding mode rounds towards nearest, then rint() differs from round in that halfway cases are rounded to even rather than away from zero.

These functions differ from the nearbyint(), nearbyintf(), and nearbyintl() functions only in that they may raise the inexact floating-point exception if the result differs in value from the argument.

An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

RETURN VALUE

Upon successful completion, these functions shall return the integer (represented as a double precision number) nearest x in the direction of the current rounding mode. ^[MX]  The result shall have the same sign as x.

^[MX] If x is NaN, a NaN shall be returned.

If x is ±0 or ±Inf, x shall be returned.

ERRORS

No errors are defined.

EXAMPLES

None.

APPLICATION USAGE

The integral value returned by these functions need not be expressible as an intmax_t. The return value should be tested before assigning it to an integer type to avoid the undefined results of an integer overflow.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

abs, ceil, feclearexcept, fetestexcept, floor, isnan, nearbyint

XBD 4.23 Treatment of Error Conditions for Mathematical Functions, <math.h>

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

Issue 6

The following changes are made for alignment with the ISO/IEC 9899:1999 standard:

• The rintf() and rintl() functions are added.

• The rint() function is no longer marked as an extension.

• The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

  IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0514 [346], XSH/TC1-2008/0515 [346], XSH/TC1-2008/0516 [346], XSH/TC1-2008/0517 [346], and XSH/TC1-2008/0518 [346] are applied.