The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group

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] [Option Start] 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.1-2017 defers to the ISO C standard. [Option End]

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] [Option Start]  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. [Option End]

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] [Option Start]  The result shall have the same sign as x. [Option End]

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

If x is ±0 or ±Inf, x shall be returned. [Option End]

ERRORS

No errors are defined.


The following sections are informative.

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 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:

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.

End of informative text.

 

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