PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

FMA(3P)                   POSIX Programmer's Manual                  FMA(3P)

PROLOG         top

       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         top

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

SYNOPSIS         top

       #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         top

       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
       operation: they shall 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.
       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         top

       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
       implementation-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         top

       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         top

       None.

APPLICATION USAGE         top

       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         top

       In many cases, clever use of floating (fused) multiply-add leads to
       much improved code; but its unexpected use by the compiler can
       undermine carefully written code. The FP_CONTRACT macro can be used
       to disallow 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 others.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       feclearexcept(3p), fetestexcept(3p)
       The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment
       of Error Conditions for Mathematical Functions, math.h(0p)

COPYRIGHT         top

       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                 2013                             FMA(3P)

Pages that refer to this page: math.h(0p)