The Open Group Base Specifications Issue 6

IEEE Std 1003.1, 2004 Edition

Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.A newer edition of this document exists here

#### NAME

nearbyint, nearbyintf, nearbyintl - floating-point rounding functions

#### SYNOPSIS

`#include <math.h>`

double nearbyint(double *x*`);`

float nearbyintf(float *x*`);`

long double nearbyintl(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 IEEE Std 1003.1-2001 defers to
the ISO C standard.

These functions shall round their argument to an integer value in floating-point format, using the current rounding direction
and without raising the inexact floating-point exception.

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 rounded integer value.

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

If *x* is ±0, ±0 shall be returned.

If *x* is ±Inf, *x* shall be returned.

^{[XSI]}
If the correct value would cause overflow, a range error shall occur and *nearbyint*(), *nearbyintf*(), and
*nearbyintl*() shall return the value of the macro ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (with the same
sign as *x*), respectively.

#### ERRORS

These functions shall fail if:

- Range Error
^{[XSI]}
The result would cause an overflow.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then *errno* shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.

*The following sections are informative.*

#### EXAMPLES

None.

#### APPLICATION USAGE

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of
each other, but at least one of them must be non-zero.

#### RATIONALE

None.

#### FUTURE DIRECTIONS

None.

#### SEE ALSO

*feclearexcept*(), *fetestexcept*(), the Base
Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of
Error Conditions for Mathematical Functions, *<math.h>*

#### CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

*End of informative text.*

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