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
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

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:

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:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes