189 lines
8.2 KiB
HTML
189 lines
8.2 KiB
HTML
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<title>fma</title>
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<basefont size="3"> <a name="fma"></a> <a name="tag_03_170"></a><!-- fma -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_170_01"></a>NAME</h4>
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<blockquote>fma, fmaf, fmal - floating-point multiply-add</blockquote>
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<h4><a name="tag_03_170_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/math.h.html">math.h</a>><br>
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<br>
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double fma(double</tt> <i>x</i><tt>, double</tt> <i>y</i><tt>, double</tt> <i>z</i><tt>);<br>
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float fmaf(float</tt> <i>x</i><tt>, float</tt> <i>y</i><tt>, float</tt> <i>z</i><tt>);<br>
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long double fmal(long double</tt> <i>x</i><tt>, long double</tt> <i>y</i><tt>, long double</tt> <i>z</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_170_03"></a>DESCRIPTION</h4>
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<blockquote>
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<div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
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requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
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the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div>
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<p>These functions shall compute (<i>x</i> * <i>y</i>) + <i>z</i>, rounded as one ternary operation: they shall
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compute the value (as if) to infinite precision and round once to the result format, according to the rounding mode characterized
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by the value of FLT_ROUNDS.</p>
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<p>An application wishing to check for error situations should set <i>errno</i> to zero and call
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<i>feclearexcept</i>(FE_ALL_EXCEPT) before calling these functions. On return, if <i>errno</i> is non-zero or
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<i>fetestexcept</i>(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.</p>
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</blockquote>
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<h4><a name="tag_03_170_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, these functions shall return (<i>x</i> * <i>y</i>) + <i>z</i>, rounded as one ternary
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operation.</p>
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<p><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If
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<i>x</i> or <i>y</i> are NaN, a NaN shall be returned.</p>
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<p>If <i>x</i> multiplied by <i>y</i> is an exact infinity and <i>z</i> is also an infinity but with the opposite sign, a domain
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error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.</p>
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<p>If one of <i>x</i> and <i>y</i> is infinite, the other is zero, and <i>z</i> is not a NaN, a domain error shall occur, and
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either a NaN (if supported), or an implementation-defined value shall be returned.</p>
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<p>If one of <i>x</i> and <i>y</i> is infinite, the other is zero, and <i>z</i> is a NaN, a NaN shall be returned and a domain
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error may occur.</p>
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<p>If <i>x</i>* <i>y</i> is not 0*Inf nor Inf*0 and <i>z</i> is a NaN, a NaN shall be returned. <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_170_05"></a>ERRORS</h4>
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<blockquote>
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<p>These functions shall fail if:</p>
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<dl compact>
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<dt>Domain Error</dt>
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<dd><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The value of <i>x</i>* <i>y</i>+ <i>z</i> is invalid, or the value <i>x</i>* <i>y</i> is invalid and <i>z</i> is not a NaN.
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<p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [EDOM]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</dd>
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<dt>Range Error</dt>
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<dd><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The result overflows.
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<p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</dd>
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</dl>
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<p>These functions may fail if:</p>
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<dl compact>
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<dt>Domain Error</dt>
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<dd><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The value <i>x</i>* <i>y</i> is invalid and <i>z</i> is a NaN.
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<p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [EDOM]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</dd>
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<dt>Range Error</dt>
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<dd><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The result underflows.
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<p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be
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raised. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_170_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_170_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of
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each other, but at least one of them must be non-zero.</p>
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</blockquote>
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<h4><a name="tag_03_170_08"></a>RATIONALE</h4>
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<blockquote>
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<p>In many cases, clever use of floating (<i>fused</i>) multiply-add leads to much improved code; but its unexpected use by the
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compiler can undermine carefully written code. The FP_CONTRACT macro can be used to disallow use of floating multiply-add; and the
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<i>fma</i>() function guarantees its use where desired. Many current machines provide hardware floating multiply-add instructions;
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software implementation can be used for others.</p>
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</blockquote>
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<h4><a name="tag_03_170_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_170_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="feclearexcept.html"><i>feclearexcept</i>()</a> , <a href="fetestexcept.html"><i>fetestexcept</i>()</a> , the Base
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Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap04.html#tag_04_18">Section 4.18, Treatment of
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Error Conditions for Mathematical Functions</a>, <a href="../basedefs/math.h.html"><i><math.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_170_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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POSIX ® is a registered Trademark of The IEEE.<br>
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