.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
.\" Distributed under GPL
.\" %%%LICENSE_END
.\"
.\" Modified 2004-11-15, Added further text on FLT_ROUNDS
.\" 	as suggested by AEB and Fabian Kreutz
.\"
.TH FMA 3  2013-07-30 "" "Linux Programmer's Manual"
.SH NAME
fma, fmaf, fmal \- floating-point multiply and add
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "double fma(double " x ", double " y ", double " z );
.br
.BI "float fmaf(float " x ", float " y ", float " z );
.br
.BI "long double fmal(long double " x ", long double " y ", long double " z );
.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 fma (),
.BR fmaf (),
.BR fmal ():
.RS 4
_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.ad
.SH DESCRIPTION
The
.BR fma ()
function computes
.IR x " * " y " + " z .
The result is rounded as one ternary operation according to the
current rounding mode (see
.BR fenv (3)).
.SH RETURN VALUE
These functions return the value of
.IR x " * " y " + " z ,
rounded as one ternary operation.

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

If
.I x
times
.I y
is an exact infinity, and
.I z
is an infinity with the opposite sign,
a domain error occurs,
and a NaN is returned.

.\" POSIX.1-2008 allows some possible differences for the following two
.\" domain error cases, but on Linux they are treated the same (AFAICS).
.\" Nevertheless, we'll mirror POSIX.1 and describe the two cases
.\" separately.
If one of
.I x
or
.I y
is an infinity, the other is 0, and
.I z
is not a NaN,
a domain error occurs, and
a NaN is returned.
.\" POSIX.1 says that a NaN or an implementation-defined value shall
.\" be returned for this case.

If one of
.I x
or
.I y
is an infinity, and the other is 0, and
.I z
is a NaN,
.\" POSIX.1 makes the domain error optional for this case.
a domain error occurs, and
a NaN is returned.

If
.I x
times
.I y
is not an infinity times zero (or vice versa), and
.I z
is a NaN,
a NaN is returned.

If the result overflows,
a range error occurs, and
an infinity with the correct sign is returned.

If the result underflows,
a range error occurs, and
a signed 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 * \fIy\fP + \fIz\fP, \
or \fIx\fP * \fIy\fP is invalid and \fIz\fP is not a NaN
.\" .I errno
.\" is set to
.\" .BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.TP
Range error: result overflow
.\" .I errno
.\" is set to
.\" .BR ERANGE .
An overflow floating-point exception
.RB ( FE_OVERFLOW )
is raised.
.TP
Range error: result underflow
.\" .I errno
.\" is set to
.\" .BR ERANGE .
An underflow floating-point exception
.RB ( FE_UNDERFLOW )
is raised.
.PP
These functions do not set
.IR errno .
.\" FIXME . Is it intentional that these functions do not set errno?
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6801
.SH VERSIONS
These functions first appeared in glibc in version 2.1.
.SH ATTRIBUTES
.SS Multithreading (see pthreads(7))
The
.BR fma (),
.BR fmaf (),
and
.BR fmal ()
functions are thread-safe.
.SH CONFORMING TO
C99, POSIX.1-2001.
.SH SEE ALSO
.BR remainder (3),
.BR remquo (3)