.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-07-27 by Walter Harms
.\" 	(walter.harms@informatik.uni-oldenburg.de)
.\"
.TH FMOD 3  2008-08-05 "" "Linux Programmer's Manual"
.SH NAME
fmod, fmodf, fmodl \- floating-point remainder function
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "double fmod(double " x ", double " y );
.br
.BI "float fmodf(float " x ", float " y );
.br
.BI "long double fmodl(long double " x ", long double " y );
.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 fmodf (),
.BR fmodl ():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
.I cc\ -std=c99
.ad b
.SH DESCRIPTION
The
.BR fmod ()
function computes the floating-point remainder of dividing \fIx\fP by
\fIy\fP.
The return value is \fIx\fP \- \fIn\fP * \fIy\fP, where \fIn\fP
is the quotient of \fIx\fP / \fIy\fP, rounded towards zero to an integer.
.SH "RETURN VALUE"
On success, these
functions return the value \fIx\fP\ \-\ \fIn\fP*\fIy\fP,
for some integer \fIn\fP,
such that the returned value has the same sign as
.I x
and a magnitude less than the magnitude of
.IR y .

If
.I x
or
.I y
is a NaN, a NaN is returned.

If
.I x
is an infinity,
a domain error occurs, and
a NaN is returned.

If
.I y
is zero,
a domain error occurs, and
a NaN is returned.

If
.I x
is +0 (\-0), and
.I y
is not zero, +0 (\-0) is returned.
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.PP
The following errors can occur:
.TP
Domain error: \fIx\fP is an infinity
.\" .I errno
.\" is set to
.\" .BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.IP
These functions do not set
.IR errno
for this case.
.\" FIXME . Is it intentional that these functions do not set errno?
.\" They do set errno for the y == 0 case, below.
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6784
.TP
Domain error: \fIy\fP is zero
.I errno
is set to
.BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.\" POSIX.1 documents an optional underflow error, but AFAICT it doesn't
.\" (can't?) occur -- mtk, Jul 2008
.SH "CONFORMING TO"
C99, POSIX.1-2001.
The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH "SEE ALSO"
.BR remainder (3)
.SH COLOPHON
This page is part of release 3.22 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
