'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" 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 2002-08-10 Walter Harms
.\"	(walter.harms@informatik.uni-oldenburg.de)
.\" Modified 2003-11-18, 2004-10-05 aeb
.\"
.TH remainder 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
drem, dremf, dreml, remainder, remainderf, remainderl \- \
floating-point remainder function
.SH LIBRARY
Math library
.RI ( libm ", " \-lm )
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
.BI "double remainder(double " x ", double " y );
.BI "float remainderf(float " x ", float " y );
.BI "long double remainderl(long double " x ", long double " y );
.PP
/* Obsolete synonyms */
.BI "[[deprecated]] double drem(double " x ", double " y );
.BI "[[deprecated]] float dremf(float " x ", float " y );
.BI "[[deprecated]] long double dreml(long double " x ", long double " y );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR remainder ():
.nf
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || _XOPEN_SOURCE >= 500
.\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.PP
.BR remainderf (),
.BR remainderl ():
.nf
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.PP
.BR drem (),
.BR dremf (),
.BR dreml ():
.nf
    /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
These
functions compute the remainder of dividing
.I x
by
.IR y .
The return value is
\fIx\fP\-\fIn\fP*\fIy\fP,
where
.I n
is the value
.IR "x\ /\ y" ,
rounded to the nearest integer.
If the absolute value of
\fIx\fP\-\fIn\fP*\fIy\fP
is 0.5,
.I n
is chosen to be even.
.PP
These functions are unaffected by the current rounding mode (see
.BR fenv (3)).
.PP
The
.BR drem ()
function does precisely the same thing.
.SH RETURN VALUE
On success, these
functions return the floating-point remainder,
\fIx\fP\-\fIn\fP*\fIy\fP.
If the return value is 0, it has the sign of
.IR x .
.PP
If
.I x
or
.I y
is a NaN, a NaN is returned.
.PP
If
.I x
is an infinity,
and
.I y
is not a NaN,
a domain error occurs, and
a NaN is returned.
.PP
If
.I y
is zero,
.\" FIXME . Instead, glibc gives a domain error even if x is a NaN
and
.I x
is not a NaN,
.\" Interestingly, remquo(3) does not have the same problem.
a domain error occurs, and
a NaN 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 and \fIy\fP is not a NaN
.I errno
is set to
.B EDOM
(but see BUGS).
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.IP
These functions do not set
.I errno
for this case.
.TP
Domain error: \fIy\fP is zero\" [XXX see bug above] and \fIx\fP is not a NaN
.I errno
is set to
.BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR drem (),
.BR dremf (),
.BR dreml (),
.BR remainder (),
.BR remainderf (),
.BR remainderl ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
.\" IEC 60559.
.TP
.BR remainder ()
.TQ
.BR remainderf ()
.TQ
.BR remainderl ()
C11, POSIX.1-2008.
.TP
.BR drem ()
.TQ
.BR dremf ()
.TQ
.BR dreml ()
None.
.SH HISTORY
.\" IEC 60559.
.TP
.BR remainder ()
.TQ
.BR remainderf ()
.TQ
.BR remainderl ()
C99, POSIX.1-2001.
.TP
.BR drem ()
4.3BSD.
.TP
.BR dremf ()
.TQ
.BR dreml ()
Tru64, glibc2.
.SH BUGS
Before glibc 2.15,
.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6779
the call
.PP
.in +4n
.EX
remainder(nan(""), 0);
.EE
.in
.PP
returned a NaN, as expected, but wrongly caused a domain error.
Since glibc 2.15, a silent NaN (i.e., no domain error) is returned.
.PP
Before glibc 2.15,
.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6783
.I errno
was not set to
.B EDOM
for the domain error that occurs when
.I x
is an infinity and
.I y
is not a NaN.
.SH EXAMPLES
The call "remainder(29.0, 3.0)" returns \-1.
.SH SEE ALSO
.BR div (3),
.BR fmod (3),
.BR remquo (3)