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

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.harms(@)informatik.uni-oldenburg.de) and Copyright 2008, Linux Foundation, written by Michael Kerrisk      %%%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