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101 lines
4.0 KiB
HTML
101 lines
4.0 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>fma (LIBM)</title>
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<meta name="description" content="fma (LIBM)">
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<meta name="keywords" content="fma (LIBM)">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
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<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Math.html#Math" rel="up" title="Math">
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<link href="fmax.html#fmax" rel="next" title="fmax">
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</head>
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<body lang="en">
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<a name="fma"></a>
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<div class="header">
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<p>
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Next: <a href="fmax.html#fmax" accesskey="n" rel="next">fmax</a>, Previous: <a href="floor.html#floor" accesskey="p" rel="prev">floor</a>, Up: <a href="Math.html#Math" accesskey="u" rel="up">Math</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="fma_002c-fmaf_002d_002d_002dfloating-multiply-add"></a>
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<h3 class="section">1.22 <code>fma</code>, <code>fmaf</code>—floating multiply add</h3>
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<a name="index-fma"></a>
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<a name="index-fmaf"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <math.h>
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double fma(double <var>x</var>, double <var>y</var>, double <var>z</var>);
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float fmaf(float <var>x</var>, float <var>y</var>, float <var>z</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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The <code>fma</code> functions compute (<var>x</var> * <var>y</var>) + <var>z</var>, rounded as one ternary
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operation: they compute the value (as if) to infinite precision and round once
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to the result format, according to the rounding mode characterized by the value
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of FLT_ROUNDS. That is, they are supposed to do this: see below.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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The <code>fma</code> functions return (<var>x</var> * <var>y</var>) + <var>z</var>, rounded as one ternary
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operation.
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</p>
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<br>
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<p><strong>Bugs</strong><br>
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This implementation does not provide the function that it should, purely
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returning "(<var>x</var> * <var>y</var>) + <var>z</var>;" with no attempt at all to provide the
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simulated infinite precision intermediates which are required. DO NOT USE THEM.
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</p>
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<p>If double has enough more precision than float, then <code>fmaf</code> should provide
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the expected numeric results, as it does use double for the calculation. But
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since this is not the case for all platforms, this manual cannot determine
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if it is so for your case.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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ANSI C, POSIX.
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</p>
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<br>
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</body>
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</html>
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