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FMA(3)		       FreeBSD Library Functions Manual			FMA(3)

NAME
     fma, fmaf -- 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);

DESCRIPTION
     The fma() and fmaf() functions return (x *	y) + z,	computed with only one
     rounding error.  Using the	ordinary multiplication	and addition opera-
     tors, 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 infin-
     ity 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	per-
     formance on machines that implement it natively.  The macros FP_FAST_FMA
     and FP_FAST_FMAF may be defined in	<math.h> to indicate that fma()	and
     fmaf() (respectively) have	comparable or faster speed than	a multiply
     operation followed	by an add operation.

IMPLEMENTATION NOTES
     In	general, fma() and fmaf() will behave as one would expect if x * y + z
     were computed with	unbounded precision and	range, then rounded to the
     precision 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() and fmaf() functions conform to ISO/IEC 9899:1999
     (``ISO C99'').  A fused multiply-add operation with virtually identical
     characteristics appears in	IEEE draft standard 754R.

HISTORY
     These routines first appeared in FreeBSD 5.4.

FreeBSD	9.2		       January 22, 2005			   FreeBSD 9.2

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | IMPLEMENTATION NOTES | SEE ALSO | STANDARDS | HISTORY

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