fma(3) — Linux manual pages

Linux manual pages	Section 3

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`():
`_ISOC99_SOURCE` \|\| `_POSIX_C_SOURCE` >= 200112L

	Note
	Link with `−lm`.

DESCRIPTION

These functions compute 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

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
`fma`(), `fmaf`(), `fmal`()	Thread safety	MT-Safe

CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.

COLOPHON

This page is part of release 4.07 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://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