<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="generator" content="Docutils 0.12: http://docutils.sourceforge.net/" />
<title>P0440r1 : Floating Point Atomic View</title>
<meta name="date" content="2016-11-09" />
<meta name="author" content="H. Carter Edwards" />
<meta name="author" content="Hans Boehm" />
<meta name="author" content="Olivier Giroux" />
<meta name="author" content="JF Bastien" />
<meta name="author" content="James Reus" />
<style type="text/css">

/*
:Author: David Goodger (goodger@python.org)
:Id: $Id: html4css1.css 7614 2013-02-21 15:55:51Z milde $
:Copyright: This stylesheet has been placed in the public domain.

Default cascading style sheet for the HTML output of Docutils.

See http://docutils.sf.net/docs/howto/html-stylesheets.html for how to
customize this style sheet.
*/

/* used to remove borders from tables and images */
.borderless, table.borderless td, table.borderless th {
  border: 0 }

table.borderless td, table.borderless th {
  /* Override padding for "table.docutils td" with "! important".
     The right padding separates the table cells. */
  padding: 0 0.5em 0 0 ! important }

.first {
  /* Override more specific margin styles with "! important". */
  margin-top: 0 ! important }

.last, .with-subtitle {
  margin-bottom: 0 ! important }

.hidden {
  display: none }

a.toc-backref {
  text-decoration: none ;
  color: black }

blockquote.epigraph {
  margin: 2em 5em ; }

dl.docutils dd {
  margin-bottom: 0.5em }

object[type="image/svg+xml"], object[type="application/x-shockwave-flash"] {
  overflow: hidden;
}

/* Uncomment (and remove this text!) to get bold-faced definition list terms
dl.docutils dt {
  font-weight: bold }
*/

div.abstract {
  margin: 2em 5em }

div.abstract p.topic-title {
  font-weight: bold ;
  text-align: center }

div.admonition, div.attention, div.caution, div.danger, div.error,
div.hint, div.important, div.note, div.tip, div.warning {
  margin: 2em ;
  border: medium outset ;
  padding: 1em }

div.admonition p.admonition-title, div.hint p.admonition-title,
div.important p.admonition-title, div.note p.admonition-title,
div.tip p.admonition-title {
  font-weight: bold ;
  font-family: sans-serif }

div.attention p.admonition-title, div.caution p.admonition-title,
div.danger p.admonition-title, div.error p.admonition-title,
div.warning p.admonition-title, .code .error {
  color: red ;
  font-weight: bold ;
  font-family: sans-serif }

/* Uncomment (and remove this text!) to get reduced vertical space in
   compound paragraphs.
div.compound .compound-first, div.compound .compound-middle {
  margin-bottom: 0.5em }

div.compound .compound-last, div.compound .compound-middle {
  margin-top: 0.5em }
*/

div.dedication {
  margin: 2em 5em ;
  text-align: center ;
  font-style: italic }

div.dedication p.topic-title {
  font-weight: bold ;
  font-style: normal }

div.figure {
  margin-left: 2em ;
  margin-right: 2em }

div.footer, div.header {
  clear: both;
  font-size: smaller }

div.line-block {
  display: block ;
  margin-top: 1em ;
  margin-bottom: 1em }

div.line-block div.line-block {
  margin-top: 0 ;
  margin-bottom: 0 ;
  margin-left: 1.5em }

div.sidebar {
  margin: 0 0 0.5em 1em ;
  border: medium outset ;
  padding: 1em ;
  background-color: #ffffee ;
  width: 40% ;
  float: right ;
  clear: right }

div.sidebar p.rubric {
  font-family: sans-serif ;
  font-size: medium }

div.system-messages {
  margin: 5em }

div.system-messages h1 {
  color: red }

div.system-message {
  border: medium outset ;
  padding: 1em }

div.system-message p.system-message-title {
  color: red ;
  font-weight: bold }

div.topic {
  margin: 2em }

h1.section-subtitle, h2.section-subtitle, h3.section-subtitle,
h4.section-subtitle, h5.section-subtitle, h6.section-subtitle {
  margin-top: 0.4em }

h1.title {
  text-align: center }

h2.subtitle {
  text-align: center }

hr.docutils {
  width: 75% }

img.align-left, .figure.align-left, object.align-left {
  clear: left ;
  float: left ;
  margin-right: 1em }

img.align-right, .figure.align-right, object.align-right {
  clear: right ;
  float: right ;
  margin-left: 1em }

img.align-center, .figure.align-center, object.align-center {
  display: block;
  margin-left: auto;
  margin-right: auto;
}

.align-left {
  text-align: left }

.align-center {
  clear: both ;
  text-align: center }

.align-right {
  text-align: right }

/* reset inner alignment in figures */
div.align-right {
  text-align: inherit }

/* div.align-center * { */
/*   text-align: left } */

ol.simple, ul.simple {
  margin-bottom: 1em }

ol.arabic {
  list-style: decimal }

ol.loweralpha {
  list-style: lower-alpha }

ol.upperalpha {
  list-style: upper-alpha }

ol.lowerroman {
  list-style: lower-roman }

ol.upperroman {
  list-style: upper-roman }

p.attribution {
  text-align: right ;
  margin-left: 50% }

p.caption {
  font-style: italic }

p.credits {
  font-style: italic ;
  font-size: smaller }

p.label {
  white-space: nowrap }

p.rubric {
  font-weight: bold ;
  font-size: larger ;
  color: maroon ;
  text-align: center }

p.sidebar-title {
  font-family: sans-serif ;
  font-weight: bold ;
  font-size: larger }

p.sidebar-subtitle {
  font-family: sans-serif ;
  font-weight: bold }

p.topic-title {
  font-weight: bold }

pre.address {
  margin-bottom: 0 ;
  margin-top: 0 ;
  font: inherit }

pre.literal-block, pre.doctest-block, pre.math, pre.code {
  margin-left: 2em ;
  margin-right: 2em }

pre.code .ln { color: grey; } /* line numbers */
pre.code, code { background-color: #eeeeee }
pre.code .comment, code .comment { color: #5C6576 }
pre.code .keyword, code .keyword { color: #3B0D06; font-weight: bold }
pre.code .literal.string, code .literal.string { color: #0C5404 }
pre.code .name.builtin, code .name.builtin { color: #352B84 }
pre.code .deleted, code .deleted { background-color: #DEB0A1}
pre.code .inserted, code .inserted { background-color: #A3D289}

span.classifier {
  font-family: sans-serif ;
  font-style: oblique }

span.classifier-delimiter {
  font-family: sans-serif ;
  font-weight: bold }

span.interpreted {
  font-family: sans-serif }

span.option {
  white-space: nowrap }

span.pre {
  white-space: pre }

span.problematic {
  color: red }

span.section-subtitle {
  /* font-size relative to parent (h1..h6 element) */
  font-size: 80% }

table.citation {
  border-left: solid 1px gray;
  margin-left: 1px }

table.docinfo {
  margin: 2em 4em }

table.docutils {
  margin-top: 0.5em ;
  margin-bottom: 0.5em }

table.footnote {
  border-left: solid 1px black;
  margin-left: 1px }

table.docutils td, table.docutils th,
table.docinfo td, table.docinfo th {
  padding-left: 0.5em ;
  padding-right: 0.5em ;
  vertical-align: top }

table.docutils th.field-name, table.docinfo th.docinfo-name {
  font-weight: bold ;
  text-align: left ;
  white-space: nowrap ;
  padding-left: 0 }

/* "booktabs" style (no vertical lines) */
table.docutils.booktabs {
  border: 0px;
  border-top: 2px solid;
  border-bottom: 2px solid;
  border-collapse: collapse;
}
table.docutils.booktabs * {
  border: 0px;
}
table.docutils.booktabs th {
  border-bottom: thin solid;
  text-align: left;
}

h1 tt.docutils, h2 tt.docutils, h3 tt.docutils,
h4 tt.docutils, h5 tt.docutils, h6 tt.docutils {
  font-size: 100% }

ul.auto-toc {
  list-style-type: none }

</style>
</head>
<body>
<div class="document" id="p0440r1-floating-point-atomic-view">
<h1 class="title">P0440r1 : Floating Point Atomic View</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">P0440r1</td>
</tr>
<tr><th class="docinfo-name">Date:</th>
<td>2016-11-09</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:ogiroux&#64;nvidia.com">ogiroux&#64;nvidia.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:jfbastien&#64;apple.com">jfbastien&#64;apple.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">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/P0440.rst">https://github.com/kokkos/ISO-CPP-Papers/blob/master/P0440.rst</a></td>
</tr>
</tbody>
</table>
<div class="section" id="revision-history">
<h1>Revision History</h1>
<div class="section" id="p0440r0">
<h2>P0440r0</h2>
<blockquote>
<ul class="simple">
<li>Apply Floating Point Atomic (P0020) to Atomic View (P0019).</li>
</ul>
</blockquote>
</div>
<div class="section" id="p0440r1">
<h2>P0440r1</h2>
<blockquote>
<ul class="simple">
<li>Editorial: add hyphenation to &quot;floating point&quot;</li>
<li>2016-11-09 Issaquah SG1 decision: move to LEWG targeting Concurrency TS V2</li>
</ul>
</blockquote>
</div>
</div>
<div class="section" id="overview-motivation">
<h1>Overview / Motivation</h1>
<p>This paper proposes an extension to the
atomic operations library [atomics]
for atomic addition on an object
conforming to <strong>atomic_view&lt;T&gt;</strong> (P0019)
where T is a <em>floating-point</em> type (N5131 3.9.1p8).
This capability is critical for high performance
computing (HPC) applications.</p>
<div class="section" id="naming">
<h2>Naming</h2>
<p>Naming will conform to the to-be-determined naming
convention selected for atomic view (P0019).
The two currently proposed atomic view naming conventions
are as follows.</p>
<blockquote>
<div class="line-block">
<div class="line">namespace std {</div>
<div class="line">namespace experimental {</div>
<div class="line-block">
<div class="line">template&lt;&gt; struct atomic_view&lt; <em>floating-point</em> &gt;;</div>
</div>
<div class="line">}}</div>
</div>
</blockquote>
<p>OR</p>
<blockquote>
<div class="line-block">
<div class="line">namespace std {</div>
<div class="line">namespace experimental {</div>
<div class="line-block">
<div class="line">template&lt;&gt; struct atomic&lt; <em>floating-point</em> &amp; &gt;;</div>
</div>
<div class="line">}}</div>
</div>
</blockquote>
</div>
</div>
<div class="section" id="proposal">
<h1>Proposal</h1>
<div class="section" id="add-to-29-2-header-atomic-synopsis">
<h2><em>add to</em> 29.2 Header &lt;atomic&gt; synopsis</h2>
<blockquote>
<div class="line-block">
<div class="line">namespace std {</div>
<div class="line-block">
<div class="line">template&lt;&gt; struct atomic_view&lt; <em>floating-point</em> &gt;;</div>
</div>
<div class="line">}</div>
</div>
</blockquote>
</div>
<div class="section" id="add-to-29-5-atomic-types">
<h2><em>add to</em> 29.5 Atomic Types</h2>
<blockquote>
<div class="line-block">
<div class="line">template&lt;&gt; struct atomic_view&lt; <em>floating-point</em> &gt; {</div>
<div class="line-block">
<div class="line">static constexpr size_t required_alignment = <em>implementation-defined</em> ;</div>
<div class="line">static constexpr bool is_always_lock_free = <em>implementation-defined</em> ;</div>
<div class="line">bool is_lock_free() const noexcept;</div>
<div class="line">void store( <em>floating-point</em> , memory_order = memory_order_seq_cst ) const noexcept;</div>
<div class="line"><em>floating-point</em> load( memory_order = memory_order_seq_cst ) const noexcept;</div>
<div class="line">operator <em>floating-point</em> () const noexcept ;</div>
<div class="line"><em>floating-point</em> exchange( <em>floating-point</em> , memory_order = memory_order_seq_cst ) const noexcept;</div>
<div class="line">bool compare_exchange_weak( <em>floating-point</em> &amp; , <em>floating-point</em> , memory_order , memory_order ) const noexcept;</div>
<div class="line">bool compare_exchange_strong( <em>floating-point</em> &amp; , <em>floating-point</em>  , memory_order , memory_order ) const noexcept;</div>
<div class="line">bool compare_exchange_weak( <em>floating-point</em> &amp; , <em>floating-point</em>  , memory_order = memory_order_seq_cst ) const noexcept;</div>
<div class="line">bool compare_exchange_strong( <em>floating-point</em> &amp;, <em>floating-point</em> , memory_order = memory_order_seq_cst ) const noexcept;</div>
<div class="line"><br /></div>
<div class="line"><em>floating-point</em> fetch_add( <em>floating-point</em> , memory_order = memory_order_seq_cst) const noexcept;</div>
<div class="line"><em>floating-point</em> fetch_sub( <em>floating-point</em> , memory_order = memory_order_seq_cst) const noexcept;</div>
<div class="line"><br /></div>
<div class="line">constexpr atomic_view() noexcept ;</div>
<div class="line">atomic_view( atomic_view &amp;&amp; ) noexcept ;</div>
<div class="line">atomic_view( const atomic_view &amp; ) noexcept ;</div>
<div class="line">atomic_view &amp; operator = ( atomic_view &amp;&amp; ) noexcept ;</div>
<div class="line">atomic_view &amp; operator = ( const atomic_view &amp; ) noexcept ;</div>
<div class="line"><em>floating-point</em> operator=( <em>floating-point</em> ) noexcept ;</div>
<div class="line"><br /></div>
<div class="line">explicit atomic_view( <em>floating-point</em> &amp; obj ) noexcept ;</div>
<div class="line">explicit constexpr operator bool () const noexcept;</div>
<div class="line"><br /></div>
<div class="line"><em>floating-point</em> operator+=( <em>floating-point</em> ) const ;</div>
<div class="line"><em>floating-point</em> operator-=( <em>floating-point</em> ) const ;</div>
</div>
<div class="line">};</div>
</div>
</blockquote>
</div>
<div class="section" id="in-29-6-6-requirements-for-operations-on-atomic-view-types">
<h2><em>in</em> 29.6.6 Requirements for operations on atomic view types</h2>
<p><em>regarding arithmetic operations</em></p>
<div class="line-block">
<div class="line"><strong>C A::fetch_</strong><em>key</em><strong>(M operand, memory_order order = memory_order_seq_cst) const noexcept;</strong></div>
</div>
<p><em>update remark as follows</em></p>
<blockquote>
<em>Remark:</em> For signed integer types, arithmetic is defined to use
two’s complement representation <s>. There</s> <u>and there</u>
are no undefined results.
<u>For floating-point types, if the result is not mathematically defined or
not in the range of representable values for its type (5p4)
the result is unspecified, but the operations
otherwise have no undefined behavior.
[Note:  Atomic arithmetic operations on <em>floating-point</em>
should conform to <strong>std::numeric_limits&lt;</strong> <em>floating-point</em> <strong>&gt;</strong>
traits associated with the floating-point type (18.3.2).
The floating-point environment (26.4) for atomic arithmetic operations
on <em>floating-point</em> may be different than the calling thread's
floating-point environment.  - end note]
</u>
For address types, the result may be an undefined address, but the operations
otherwise have no undefined behavior.</blockquote>
</div>
</div>
</div>
</body>
</html>
