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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
<!-- Converted by db4-upgrade version 1.1 -->
<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="atomicCompSwap">
<info>
<copyright>
<year>2012-2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>atomicCompSwap</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>atomicCompSwap</refname>
<refpurpose>perform an atomic compare-exchange operation to a variable</refpurpose>
</refnamediv>
<refsynopsisdiv><title>Declaration</title>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>atomicCompSwap</function></funcdef>
<paramdef>inout int <parameter>mem</parameter></paramdef>
<paramdef>uint <parameter>compare</parameter></paramdef>
<paramdef>uint <parameter>data</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>uint <function>atomicCompSwap</function></funcdef>
<paramdef>inout uint <parameter>mem</parameter></paramdef>
<paramdef>uint <parameter>compare</parameter></paramdef>
<paramdef>uint <parameter>data</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 xml:id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>mem</parameter></term>
<listitem>
<para>
The variable to use as the target of the operation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>data</parameter></term>
<listitem>
<para>
The data to be compared and potentially exchanged with <parameter>mem</parameter>.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description"><title>Description</title>
<para>
<function>atomicCompSwap</function> performs an atomic comparison of <parameter>compare</parameter> with the contents of
<parameter>mem</parameter>. If the content of <parameter>mem</parameter> is equal to <parameter>compare</parameter>,
then the content of <parameter>data</parameter> is written into <parameter>mem</parameter>,
otherwise the content of <parameter>mem</parameter> is unmodifed.
The function returns the original content of <parameter>mem</parameter> regardless of the
outcome of the comparison. The contents of the memory being updated by the atomic operation are
guaranteed not to be modified by any other assignment or atomic memory function in any shader
invocation between the time the original value is read and the time the new value is written.
</para>
<para>
Atomic memory functions are supported only for a limited set of variables. A shader will fail to compile
if the value passed to the mem argument of an atomic memory function does not correspond to a buffer or
shared variable. It is acceptable to pass an element of an array or a single component of a vector to the
mem argument of an atomic memory function, as long as the underlying array or vector is a buffer or
shared variable.
</para>
</refsect1>
<refsect1 xml:id="versions"><title>Version Support</title>
<informaltable>
<tgroup cols="13" align="left">
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="funchead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry>atomicCompSwap</entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="version.xml" xpointer="xpointer(/*/*[@role='43']/*)"/>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 xml:id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>atomicAdd</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>atomicAnd</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>atomicOr</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>atomicXor</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>atomicMin</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>atomicMax</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>atomicExchange</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 xml:id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"/> 2011-2014 Khronos Group.
This material may be distributed subject to the terms and conditions set forth in
the Open Publication License, v 1.0, 8 June 1999.
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
</para>
</refsect1>
</refentry>
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