# fma(), fmaf(), fmal()

Multiply two floating-point numbers and then add a third number

## 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 );

## Arguments:

x, y
The numbers that you want to multiply together.
z
The number you want to add to the product.

## Library:

libm

Use the -l m option to qcc to link against this library.

## Description:

The fma(), fmaf(), and fmal() (“fused multiply-add”) functions calculate (x * y) + z, rounded as one ternary operation. That is, they compute the value to infinite precision and then round the result once, according to the current rounding mode as specified by FLT_ROUNDS.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

• Call feclearexcept(FE_ALL_EXCEPT) before calling fma(), fmaf(), or fmal().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

## Returns:

(x * y) + z, rounded as one ternary operation.

If: These functions return: Errors:
The result overflows Inf FE_OVERFLOW
The result underflows The correct result, after rounding FE_UNDERFLOW
x or y is NaN NaN
x * y is an exact infinity, and z is also an infinity but with the opposite sign NaN FE_INVALID
One of x and y is infinite, the other is zero, and z isn't a NaN NaN FE_INVALID
One of x and y is infinite, the other is zero, and z is NaN NaN FE_INVALID
x * y isn't 0.0 * Inf or Inf * 0.0, and z is NaN NaN

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

## Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No