man3/remainder.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" 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 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
drem, dremf, dreml, remainder, remainderf, remainderl \- \
floating-point remainder function
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
/* The C99 versions */
.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 "double drem(double " x ", double " y );
.BI "float dremf(float " x ", float " y );
.BI "long double dreml(long double " x ", long double " y );
.PP
.fi
Link with \fI\-lm\fP.
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.ad l
.BR remainder ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
    || _XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.br
.BR remainderf (),
.BR remainderl ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.br
.BR drem (),
.BR dremf (),
.BR dreml ():
.RS 4
/* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.ad b
.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
.BR EDOM
(but see BUGS).
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.IP
These functions do not set
.IR 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).
.TS
allbox;
lbw26 lb lb
l l l.
Interface	Attribute	Value
T{
.BR drem (),
.BR dremf (),
.BR dreml (),
.br
.BR remainder (),
.BR remainderf (),
.br
.BR remainderl ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
.\" IEC 60559.
The functions
.BR remainder (),
.BR remainderf (),
and
.BR remainderl ()
are specified in C99, POSIX.1-2001, and POSIX.1-2008.
.PP
The function
.BR drem ()
is from 4.3BSD.
The
.I float
and
.I "long double"
variants
.BR dremf ()
and
.BR dreml ()
exist on some systems, such as Tru64 and glibc2.
Avoid the use of these functions in favor of
.BR remainder ()
etc.
.SH BUGS
Before glibc 2.15,
.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6779
the call
.PP
    remainder(nan(""), 0);
.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,
.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6783
.I errno
was not set to
.BR EDOM
for the domain error that occurs when
.I x
is an infinity and
.I y
is not a NaN.
.I errno was not set
.SH EXAMPLE
The call "remainder(29.0, 3.0)" returns \-1.
.SH SEE ALSO
.BR div (3),
.BR fmod (3),
.BR remquo (3)