fma(3p) — Linux manual page

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.1‐2017 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.1‐2017, Section 4.20,
       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 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                           FMA(3P)

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