.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\" Distributed under GPL, 2002-07-27 Walter Harms
.\" Modified 2004-11-15, Added further text on FLT_ROUNDS
.\" 	as suggested by AEB and Fabian Kreutz
.\"
.TH FMA 3  2008-08-11 "" "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 ():
_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
.I cc\ -std=c99
.ad b
.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.

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.

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 "CONFORMING TO"
C99, POSIX.1-2001.
.SH "SEE ALSO"
.BR remainder (3),
.BR remquo (3)