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FMA(3P)                    POSIX Programmer's Manual                   FMA(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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
       The functionality described on this reference page is aligned with  the
       ISO C  standard.  Any  conflict between the requirements described here
       and the ISO C standard is unintentional. This  volume  of  POSIX.1-2008
       defers to the ISO C standard.
       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  the  result  overflows  or underflows, a range error may occur.  On
       systems that support the IEC 60559 Floating-Point option, if the result
       overflows a range error shall occur.
       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.
       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.
       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 POSIX.1-2008, Section 4.19, 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, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) 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.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                              FMA(3P)