The Open Group Base Specifications Issue 8
IEEE Std 1003.1-2024
Copyright © 2001-2024 The 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.1-2024 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 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:

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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