fma (3)
Leading comments
Copyright 2002 Walter Harms (walter.harms@informatik.unioldenburg.de) and Copyright 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpages@gmail.com> %%%LICENSE_START(GPL_NOVERSION_ONELINE) Distributed under GPL %%%LICENSE_END Modified 20041115, Added further text on FLT_ROUNDS as suggested by AEB and Fabian Kreutz
NAME
fma, fmaf, fmal  floatingpoint multiply and addSYNOPSIS
#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():

_XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
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 floatingpoint exception (FE_INVALID) is raised.
 Range error: result overflow
 An overflow floatingpoint exception (FE_OVERFLOW) is raised.
 Range error: result underflow
 An underflow floatingpoint 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  MTSafe 