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FMA(P)			   POSIX Programmer's Manual			FMA(P)

NAME
       fma, fmaf, fmal - floating-point multiply-add

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
       These functions shall compute (x * y) + z, rounded as one ternary oper‐
       ation: they shall compute the value (as if) to infinite	precision  and
       round once to the result format, according to the rounding mode charac‐
       terized by the value of FLT_ROUNDS.

       An application wishing to check for error situations should  set	 errno
       to  zero	 and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
       functions.  On return, if errno is non-zero or  fetestexcept(FE_INVALID
       |  FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
       occurred.

RETURN VALUE
       Upon successful completion, these functions shall return	 (x * y) +  z,
       rounded as one ternary operation.

       If x or y are NaN, a NaN shall be returned.

       If x multiplied by y is an exact infinity and z is also an infinity but
       with the opposite sign, a domain error shall occur, and	either	a  NaN
       (if supported), or an implementation-defined value shall be returned.

       If one of x and y is infinite, the other is zero, and z is not a NaN, a
       domain error shall occur, and either a NaN (if supported), or an imple‐
       mentation-defined value shall be returned.

       If one of x and y is infinite, the other is zero, and z is a NaN, a NaN
       shall be returned and a domain error may occur.

       If x* y is not 0*Inf nor Inf*0 and z is a NaN, a NaN shall be returned.

ERRORS
       These functions shall fail if:

       Domain Error
	      The value of x* y+ z is invalid, or the value x*	y  is  invalid
	      and z is not a NaN.

       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
       then  errno  shall  be  set  to	[EDOM].	 If  the  integer   expression
       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero,  then  the invalid
       floating-point exception shall be raised.

       Range Error
	      The result overflows.

       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
       then  errno  shall  be  set  to	[ERANGE].  If  the  integer expression
       (math_errhandling & MATH_ERREXCEPT)  is	non-zero,  then	 the  overflow
       floating-point exception shall be raised.

       These functions may fail if:

       Domain Error
	      The value x* y is invalid and z is a NaN.

       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
       then  errno  shall  be  set  to	[EDOM].	 If  the  integer   expression
       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero,  then  the invalid
       floating-point exception shall be raised.

       Range Error
	      The result underflows.

       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
       then  errno  shall  be  set  to	[ERANGE].  If  the  integer expression
       (math_errhandling & MATH_ERREXCEPT) is  non-zero,  then	the  underflow
       floating-point exception shall be raised.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       On   error,   the   expressions	(math_errhandling  &  MATH_ERRNO)  and
       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
       at least one of them must be non-zero.

RATIONALE
       In  many	 cases,	 clever	 use of floating (fused) multiply-add leads to
       much improved code; but its unexpected use by the compiler  can	under‐
       mine  carefully written code. The FP_CONTRACT macro can be used to dis‐
       allow use of floating multiply-add; and the fma()  function  guarantees
       its  use where desired. Many current machines provide hardware floating
       multiply-add instructions; software implementation can be used for oth‐
       ers.

FUTURE DIRECTIONS
       None.

SEE ALSO
       feclearexcept()	,  fetestexcept()  ,  the  Base	 Definitions volume of
       IEEE Std 1003.1-2001, Section 4.18, Treatment of Error  Conditions  for
       Mathematical Functions, <math.h>

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003	by  the	 Institute  of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained	online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003				FMA(P)
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