# fma man page

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***);**

`Link with `

*-lm*.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):**fma**(), **fmaf**(), **fmal**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

## 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.

## See Also

## Colophon

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## Referenced By

fmaf(3) and fmal(3) are aliases of fma(3).