FMA(3) Library Functions Manual FMA(3) NAME fma, fmaf, fmal -- fused multiply-add LIBRARY Math Library (libm, -lm) 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); DESCRIPTION The fma(), fmaf(), and fmal() functions return (x * y) + z, computed with only one rounding error. Using the ordinary multiplication and addition operators, by contrast, results in two roundings: one for the intermediate product and one for the final result. For instance, the expression 1.2e100 * 2.0e208 - 1.4e308 produces infinity due to overflow in the intermediate product, whereas fma(1.2e100, 2.0e208, -1.4e308) returns approximately 1.0e308. The fused multiply-add operation is often used to improve the accuracy of calculations such as dot products. It may also be used to improve perfor- mance on machines that implement it natively. The macros FP_FAST_FMA, FP_FAST_FMAF and FP_FAST_FMAL may be defined in <math.h> to indicate that fma(), fmaf(), and fmal() (respectively) have comparable or faster speed than a multiply operation followed by an add operation. IMPLEMENTATION NOTES In general, these routines will behave as one would expect if x * y + z were computed with unbounded precision and range, then rounded to the pre- cision of the return type. However, on some platforms, if z is NaN, these functions may not raise an exception even when the computation of x * y would have otherwise generated an invalid exception. SEE ALSO fenv(3), math(3) STANDARDS The fma(), fmaf(), and fmal() functions conform to ISO/IEC 9899:1999 ("ISO C99"). A fused multiply-add operation with virtually identical char- acteristics appears in IEEE draft standard 754R. HISTORY The fma() and fmaf() routines first appeared in FreeBSD 5.4, and fmal() ap- peared in FreeBSD 6.0. FreeBSD 15.1 January 22, 2005 FMA(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | IMPLEMENTATION NOTES | SEE ALSO | STANDARDS | HISTORY
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=fma&sektion=3&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>