fma(3) — Linux manual pages

Linux manual pages	Section 3: Subroutines

Name

fma, fmaf, fmal — floating-point multiply and add

Synopsis

#include <math.h>

`double fma(`	double `x`,
	double `y`,
	double `z)`;

`float fmaf(`	float `x`,
	float `y`,
	float `z)`;

`long double fmal(`	long double `x`,
	long double `y`,
	long double `z)`;

Note

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
`fma`(), `fmaf`(), `fmal`():
`_XOPEN_SOURCE` >= 600 \|\| `_ISOC99_SOURCE` \|\| `_POSIX_C_SOURCE` >= 200112L;
or cc `-std=c99`

	Note
	Link with `−lm`.

DESCRIPTION

The fma() function computes x * y + z. The result is rounded as one ternary operation according to the current rounding mode (see fenv(3)).

RETURN VALUE

These functions return the value of x * y + z, rounded as one ternary operation.

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

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

If one of x or y is an infinity, the other is 0, and z is not a NaN, a domain error occurs, and a NaN is returned.

If one of x or y is an infinity, and the other is 0, and z is a NaN, a domain error occurs, and a NaN is returned.

If x times y is not an infinity times zero (or vice versa), and 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.

ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: x * y + z, or x * y is invalid and z is not a NaN: An invalid floating-point exception (FE_INVALID) is raised.
Range error: result overflow: An overflow floating-point exception (FE_OVERFLOW) is raised.
Range error: result underflow: An underflow floating-point exception (FE_UNDERFLOW) is raised.

These functions do not set errno.

VERSIONS

These functions first appeared in glibc in version 2.1.

ATTRIBUTES

Multithreading (see pthreads(7))

The fma(), fmaf(), and fmal() functions are thread-safe.

CONFORMING TO

C99, POSIX.1-2001.

COLOPHON

This page is part of release 3.54 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man−pages/.

Copyright 2002 Walter Harms (walter.harmsinformatik.uni-oldenburg.de)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpagesgmail.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