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[thirdparty/man-pages.git] / man3 / round.3

.\" Copyright 2001 Andries Brouwer <aeb@cwi.nl>.
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
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.TH ROUND 3  2010-09-20 "" "Linux Programmer's Manual"
.SH NAME
round, roundf, roundl \- round to nearest integer, away from zero
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "double round(double " x );
.br
.BI "float roundf(float " x );
.br
.BI "long double roundl(long double " x );
.fi
.sp
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR round (),
.BR roundf (),
.BR roundl ():
.RS 4
_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.ad
.SH DESCRIPTION
These functions round \fIx\fP to the nearest integer, but
round halfway cases away from zero (regardless of the current rounding
direction, see
.BR fenv (3)),
instead of to the nearest even integer like
.BR rint (3).

For example,
.IR round(0.5)
is 1.0, and
.IR round(\-0.5)
is \-1.0.
.SH RETURN VALUE
These functions return the rounded integer value.

If \fIx\fP is integral, +0, \-0, NaN,  or infinite,
\fIx\fP itself is returned.
.SH ERRORS
No errors occur.
POSIX.1-2001 documents a range error for overflows, but see NOTES.
.SH VERSIONS
These functions first appeared in glibc in version 2.1.
.SH CONFORMING TO
C99, POSIX.1-2001.
.SH NOTES
POSIX.1-2001 contains text about overflow (which might set
.I errno
to
.BR ERANGE ,
or raise an
.B FE_OVERFLOW
exception).
In practice, the result cannot overflow on any current machine,
so this error-handling stuff is just nonsense.
.\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point.
(More precisely, overflow can happen only when the maximum value
of the exponent is smaller than the number of mantissa bits.
For the IEEE-754 standard 32-bit and 64-bit floating-point numbers
the maximum value of the exponent is 128 (respectively, 1024),
and the number of mantissa bits is 24 (respectively, 53).)

If you want to store the rounded value in an integer type,
you probably want to use one of the functions described in
.BR lround (3)
instead.
.SH SEE ALSO
.BR ceil (3),
.BR floor (3),
.BR lround (3),
.BR nearbyint (3),
.BR rint (3),
.BR trunc (3)