fma.3p (6196B)
- '\" et
- .TH FMA "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH 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.
- .\"
- .SH NAME
- fma,
- fmaf,
- fmal
- \(em floating-point multiply-add
- .SH SYNOPSIS
- .LP
- .nf
- #include <math.h>
- .P
- double fma(double \fIx\fP, double \fIy\fP, double \fIz\fP);
- float fmaf(float \fIx\fP, float \fIy\fP, float \fIz\fP);
- long double fmal(long double \fIx\fP, long double \fIy\fP, long double \fIz\fP);
- .fi
- .SH 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\(hy2017 defers to the ISO\ C standard.
- .P
- These functions shall compute (\fIx\fR\ *\ \fIy\fR)\ +\ \fIz\fR,
- 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.
- .P
- An application wishing to check for error situations should set
- .IR errno
- to zero and call
- .IR feclearexcept (FE_ALL_EXCEPT)
- before calling these functions. On return, if
- .IR errno
- is non-zero or \fIfetestexcept\fR(FE_INVALID | FE_DIVBYZERO |
- FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
- .SH "RETURN VALUE"
- Upon successful completion, these functions shall return
- (\fIx\fR\ *\ \fIy\fR)\ + \fIz\fR, rounded as one ternary operation.
- .P
- 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.
- .P
- If
- .IR x
- or
- .IR y
- are NaN, a NaN shall be returned.
- .P
- If
- .IR x
- multiplied by
- .IR y
- is an exact infinity and
- .IR 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.
- .P
- If one of
- .IR x
- and
- .IR y
- is infinite, the other is zero, and
- .IR z
- is not a NaN, a domain error shall occur, and either a NaN (if
- supported), or an implementation-defined value shall be returned.
- .P
- If one of
- .IR x
- and
- .IR y
- is infinite, the other is zero, and
- .IR z
- is a NaN, a NaN shall be returned and a domain error may occur.
- .P
- If
- .IR x *\c
- .IR y
- is not 0*Inf nor Inf*0 and
- .IR z
- is a NaN, a NaN shall be returned.
- .SH ERRORS
- These functions shall fail if:
- .IP "Domain\ Error" 12
- The value of
- .IR x *\c
- .IR y +\c
- .IR z
- is invalid, or the value
- .IR x *\c
- .IR y
- is invalid and
- .IR z
- is not a NaN.
- .RS 12
- .P
- If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
- non-zero, then
- .IR errno
- shall be set to
- .BR [EDOM] .
- If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
- non-zero, then the invalid floating-point exception shall be raised.
- .RE
- .IP "Range\ Error" 12
- The result overflows.
- .RS 12
- .P
- If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
- non-zero, then
- .IR errno
- shall be set to
- .BR [ERANGE] .
- If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
- non-zero, then the overflow floating-point exception shall be raised.
- .RE
- .br
- .P
- These functions may fail if:
- .IP "Domain\ Error" 12
- The value
- .IR x *\c
- .IR y
- is invalid and
- .IR z
- is a NaN.
- .RS 12
- .P
- If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
- non-zero, then
- .IR errno
- shall be set to
- .BR [EDOM] .
- If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
- non-zero, then the invalid floating-point exception shall be raised.
- .RE
- .IP "Range\ Error" 12
- The result underflows.
- .RS 12
- .P
- If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
- non-zero, then
- .IR errno
- shall be set to
- .BR [ERANGE] .
- If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
- non-zero, then the underflow floating-point exception shall be raised.
- .RE
- .IP "Range\ Error" 12
- The result overflows.
- .RS 12
- .P
- If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
- non-zero, then
- .IR errno
- shall be set to
- .BR [ERANGE] .
- If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
- non-zero, then the overflow floating-point exception shall be raised.
- .RE
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "APPLICATION USAGE"
- On error, the expressions (\fImath_errhandling\fR & MATH_ERRNO) and
- (\fImath_errhandling\fR & MATH_ERREXCEPT) are independent of each
- other, but at least one of them must be non-zero.
- .SH RATIONALE
- In many cases, clever use of floating (\fIfused\fR) 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
- \fIfma\fR()
- function guarantees its use where desired. Many current machines
- provide hardware floating multiply-add instructions; software
- implementation can be used for others.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIfeclearexcept\fR\^(\|)",
- .IR "\fIfetestexcept\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "Section 4.20" ", " "Treatment of Error Conditions for Mathematical Functions",
- .IR "\fB<math.h>\fP"
- .\"
- .SH COPYRIGHT
- 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 .
- .PP
- 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 .