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# FMA

Section: Linux Programmer's Manual (3)
Updated: 2008-10-06

## 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);
```

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

fma(), fmaf(), fmal(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99

## 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.

## CONFORMING TO

C99, POSIX.1-2001.

remainder(3), remquo(3)

## COLOPHON

This page is part of release 3.21 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/.

## Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
COLOPHON

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