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<title>P0020r2 : Floating Point Atomic</title>
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<body>
<div class="document" id="p0020r2-floating-point-atomic">
<h1 class="title">P0020r2 : Floating Point Atomic</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr class="field"><th class="docinfo-name">Project:</th><td class="field-body">ISO JTC1/SC22/WG21: Programming Language C++</td>
</tr>
<tr class="field"><th class="docinfo-name">Number:</th><td class="field-body">P0020r2</td>
</tr>
<tr><th class="docinfo-name">Date:</th>
<td>2016-03-14</td></tr>
<tr class="field"><th class="docinfo-name">Reply-to:</th><td class="field-body"><a class="reference external" href="mailto:hcedwar&#64;sandia.gov">hcedwar&#64;sandia.gov</a></td>
</tr>
<tr><th class="docinfo-name">Author:</th>
<td>H. Carter Edwards</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference external" href="mailto:hcedwar&#64;sandia.gov">hcedwar&#64;sandia.gov</a></td></tr>
<tr><th class="docinfo-name">Author:</th>
<td>Hans Boehm</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference external" href="mailto:hboehm&#64;google.com">hboehm&#64;google.com</a></td></tr>
<tr><th class="docinfo-name">Author:</th>
<td>Olivier Giroux</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference external" href="mailto:hboehm&#64;google.com">hboehm&#64;google.com</a></td></tr>
<tr><th class="docinfo-name">Author:</th>
<td>JF Bastien</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference external" href="mailto:jfb&#64;google.com">jfb&#64;google.com</a></td></tr>
<tr><th class="docinfo-name">Author:</th>
<td>James Reus</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference external" href="mailto:reus1&#64;llnl.gov">reus1&#64;llnl.gov</a></td></tr>
<tr class="field"><th class="docinfo-name">Audience:</th><td class="field-body">SG1 Concurrency, Library Evolution</td>
</tr>
<tr class="field"><th class="docinfo-name">URL:</th><td class="field-body"><a class="reference external" href="https://github.com/kokkos/ISO-CPP-Papers/blob/master/P0020.rst">https://github.com/kokkos/ISO-CPP-Papers/blob/master/P0020.rst</a></td>
</tr>
</tbody>
</table>
<div class="section" id="motivation">
<h1>1&nbsp;&nbsp;&nbsp;Motivation</h1>
<p>This paper proposes an extension to the atomic operations library [atomics]
for atomic addition on an object conforming to the <em>atomic-view-concept</em>
(see P0019, Atomic View)
instantiated for a floating point type.
A class conforming to the <em>atomic-view-concept</em> shall also provide
the following operations when T is a floating-point type.
This capability is critical for high performance computing (HPC) applications.</p>
</div>
<div class="section" id="proposal">
<h1>2&nbsp;&nbsp;&nbsp;Proposal</h1>
<p>[Note: In 3.9.1p8 floating point types are also refered to as <em>floating</em> types. - end note]</p>
<p>Add to 29.5, Atomic Types, before 29.5p1.</p>
<blockquote>
<div class="line-block">
<div class="line">template&lt;&gt; struct atomic&lt; <em>floating</em> &gt; {</div>
<div class="line-block">
<div class="line"><em>floating</em> fetch_add( <em>floating</em> operand , memory_order order = memory_order_seq_cst ) volatile noexcept;</div>
<div class="line"><em>floating</em> fetch_add( <em>floating</em> operand , memory_order order = memory_order_seq_cst ) noexcept;</div>
<div class="line"><em>floating</em> fetch_sub( <em>floating</em> operand , memory_order order = memory_order_seq_cst ) volatile noexcept;</div>
<div class="line"><em>floating</em> fetch_sub( <em>floating</em> operand , memory_order order = memory_order_seq_cst ) noexcept;</div>
<div class="line"><em>floating</em> operator+=( <em>floating</em> operand ) volatile noexcept;</div>
<div class="line"><em>floating</em> operator+=( <em>floating</em> operand ) noexcept;</div>
<div class="line"><em>floating</em> operator-=( <em>floating</em> operand ) volatile noexcept;</div>
<div class="line"><em>floating</em> operator-=( <em>floating</em> operand ) noexcept;</div>
</div>
<div class="line">};</div>
<div class="line"><br /></div>
<div class="line">template&lt;&gt; struct <em>atomic-view-concept</em> &lt; <em>floating</em> &gt; {</div>
<div class="line-block">
<div class="line"><em>floating</em> fetch_add( <em>floating</em> operand , memory_order order = memory_order_seq_cst ) const noexcept;</div>
<div class="line"><em>floating</em> fetch_sub( <em>floating</em> operand , memory_order order = memory_order_seq_cst ) const noexcept;</div>
<div class="line"><em>floating</em> operator+=( <em>floating</em> operand ) const noexcept;</div>
<div class="line"><em>floating</em> operator-=( <em>floating</em> operand ) const noexcept;</div>
</div>
<div class="line">};</div>
</div>
</blockquote>
<p>Insert into the listed types in 29.5p5:</p>
<blockquote>
<em>floating</em> specializations</blockquote>
<p>Insert new paragraph after 29.6.5p30.</p>
<blockquote>
Remark: For <em>floating</em> types atomic arithmatic operations
<em>should</em> conform to <strong>std::numeric_limits&lt;</strong> <em>floating</em> <strong>&gt;</strong> (18.3.2)
traits associated with the floating point type.
The floating point environment (26.3) for these operations may be
different that the calling thread's floating point environment.</blockquote>
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