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.\" Copyright 2001 Andries Brouwer <aeb@cwi.nl>.
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.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH ROUND 3 2017-09-15 "" "Linux Programmer's Manual"
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.SH NAME
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round, roundf, roundl \- round to nearest integer, away from zero
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.SH SYNOPSIS
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.nf
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.B #include <math.h>
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.PP
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.BI "double round(double " x );
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.BI "float roundf(float " x );
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.BI "long double roundl(long double " x );
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.fi
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.PP
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Link with \fI\-lm\fP.
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.PP
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.PP
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.ad l
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.BR round (),
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.BR roundf (),
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.BR roundl ():
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.RS 4
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_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
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.RE
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.ad
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.SH DESCRIPTION
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These functions round
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.I x
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to the nearest integer, but
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round halfway cases away from zero (regardless of the current rounding
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direction, see
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.BR fenv (3)),
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instead of to the nearest even integer like
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.BR rint (3).
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.PP
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For example,
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.IR round(0.5)
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is 1.0, and
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.IR round(\-0.5)
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is \-1.0.
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.SH RETURN VALUE
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These functions return the rounded integer value.
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.PP
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If
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.I x
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is integral, +0, \-0, NaN, or infinite,
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.I x
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itself is returned.
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.SH ERRORS
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No errors occur.
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POSIX.1-2001 documents a range error for overflows, but see NOTES.
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.SH VERSIONS
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These functions first appeared in glibc in version 2.1.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lbw27 lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR round (),
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.BR roundf (),
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.BR roundl ()
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T} Thread safety MT-Safe
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.TE
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.SH CONFORMING TO
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C99, POSIX.1-2001, POSIX.1-2008.
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.SH NOTES
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POSIX.1-2001 contains text about overflow (which might set
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.I errno
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to
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.BR ERANGE ,
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or raise an
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.B FE_OVERFLOW
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exception).
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In practice, the result cannot overflow on any current machine,
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so this error-handling stuff is just nonsense.
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.\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point.
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(More precisely, overflow can happen only when the maximum value
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of the exponent is smaller than the number of mantissa bits.
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For the IEEE-754 standard 32-bit and 64-bit floating-point numbers
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the maximum value of the exponent is 128 (respectively, 1024),
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and the number of mantissa bits is 24 (respectively, 53).)
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.PP
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If you want to store the rounded value in an integer type,
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you probably want to use one of the functions described in
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.BR lround (3)
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instead.
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.SH SEE ALSO
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.BR ceil (3),
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.BR floor (3),
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.BR lround (3),
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.BR nearbyint (3),
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.BR rint (3),
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.BR trunc (3)
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.SH COLOPHON
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This page is part of release 4.15 of the Linux
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.I man-pages
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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\%https://www.kernel.org/doc/man\-pages/.
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