- floating-point multiply-add
c99 [ flag... ] file... -lm [ library... ] #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);
These functions compute (x * y) + z, rounded as one ternary operation. They compute the value (as if) to infinite precision and round once to the result format, according to the rounding mode characterized by the value of FLT_ROUNDS.
Upon successful completion, these functions return (x * y) + z, rounded as one ternary operation.
If x or y are NaN, a NaN is returned.
If x multiplied by y is an exact infinity and z is also an infinity but with the opposite sign, a domain error occurs and a NaN is returned.
If one of x and y is infinite, the other is 0, and z is not a NaN, a domain error occurs and a NaN is returned.
If x*y is not 0*Inf nor Inf*0 and z is a NaN, a NaN is returned.
These functions will fail if:
The value of x*y+z is invalid or the value x*y is invalid.
If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the invalid floating-point exception will be raised.
The result overflows.
If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the overflow floating-point exception will be raised.
An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.
See attributes(5) for descriptions of the following attributes: