sdk/2.1/docs/man/xhtml/attributes-types.html - external/github.com/KhronosGroup/OpenCL-Registry - Git at Google

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd">
 <!-- saved from url=(0013)about:internet -->
 <?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" xmlns:xlink="http://www.w3.org/1999/xlink" pref:renderer="mathplayer-dl">
   <head>
     <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
     <style xmlns="" type="text/css">
     /* This style sets a margin around the entire page */
         html, body {
             margin: 10px;
         }

         p {
             font: normal 16px verdana, sans-serif;
             margin: 0;
             padding-bottom:12px;
         }

         h1 {
             font: bold 25px verdana, sans-serif;
             margin-top: 0;
             margin-bottom: 3px;
             padding-top: 0;
             padding-bottom: 0;
         }

         h2 {
             font: bold 19px verdana, sans-serif;
             margin-top: 28px;
             margin-bottom: 3px;
             padding-top: 0;
             padding-bottom: 0;
         }

         h3 {
             font: bold 19px verdana, sans-serif !important;
             margin-top: 28px;
             margin-bottom: 3px;
             padding-top: 0;
             padding-bottom: 0;
         }

         li {
             font: normal 16px verdana, sans-serif;
             margin-top: 0;
             margin-bottom: 18px;
             padding-top: 0;
             padding-bottom: 0;
         }

         .pdparam {
             font: italic 16px verdana, sans-serif;
         }

                 .term {
                         font: italic 16px verdana, sans-serif;
                         font-weight: normal;
                 }

                 .type {
                         font: normal 16px verdana, sans-serif !important;
                 }

                 .parameter {
                         font-style: italic;
                         }

         a:link, a:visited {
             color: blue;
             text-decoration: none;
             font: normal 16px;
         }

         a:hover {
             background-color: #FFFF99;
             font: normal 16px;
         }

         div.funcsynopsis {
             text-align: left;
             background-color: #e6e6e6;
             font: normal 16px verdana, sans-serif;
                         padding-top: 10px;
                         padding-bottom: 10px;
         }

         div.funcsynopsis table {
             border-collapse: separate;
             font: normal 16px verdana, sans-serif;
         }

         div.funcsynopsis td {
             background-color: #e6e6e6;
             border: 0 solid #000;
             padding: 1px;
             font: normal 16px verdana, sans-serif;
         }

         div.refsect1 {
             font-family: verdana, sans-serif;
             font-size: 16px;
         }

         code.constant {
             font: normal 16px courier new, monospace !important;
         }

                 span.errorname {
             font: normal 16px verdana, sans-serif !important;
         }

         code.function {
             font: bold 16px verdana, sans-serif !important;
         }

         b.fsfunc {
             font: bold 16px verdana, sans-serif !important;
         }

         code.varname {
             font: italic 16px verdana, sans-serif;
         }

         code.replaceable {
             font: italic 16px courier new, monospace;
         }

         code.funcdef {
             font: normal 16px verdana, sans-serif !important;
         }

         .citerefentry {
             font: normal 16px verdana, sans-serif !important;
         }

         .parameter {
             font-style: italic;
         }

         code.fsfunc {
             font: normal 16px verdana, sans-serif !important;
         }

         /* PARAMETER: This style controls spacing between the terms in Parameter section */
         dt {
             margin-top: 15px;
         }

         /* TABLES: These styles apply to all tables OTHER than the Synopsis and Example tables */
         div.refsect1 table {
             width: 100%;
                         margin-top: 10px;
             background-color: #FFF;
                         border-collapse: collapse;
                         border-color: #000;
             border-width: 1px;
                         font: normal 16px verdana, sans-serif;
         }

         div.refsect1 th {
                         border-collapse: collapse;
                         border-color: #000;
             border-width: 1px;
             font: bold 16px verdana, sans-serif;
         }

         div.refsect1 td {
             background-color: #FFF;
             padding: 5px;
             vertical-align: text-top;
                         border-collapse: collapse;
                         border-color: #000;
             border-width: 1px;
             font: normal 16px verdana, sans-serif;
         }

                   div.refsect1 p{
             font: normal 16px verdana, sans-serif;
             margin-top: 8px;
             margin-bottom: 8px;
             padding-top: 0;
             padding-bottom: 0;
         }


         /* EXAMPLE: These styles apply only to the Example section */
         div.refsect2 {
             font: normal 16px courier new, monospace !important;
         }

         div.refsect2 table {
             margin-top: 0;
             background-color: #e6e6e6;
             width: 100%;
             border: 0 solid #000;
             padding: 2px;
             font: normal 16px courier new, monospace !important;
         }

         div.refsect2 td {
             background-color: #e6e6e6;
             font: normal 16px courier new, monospace !important;
                         white-space:pre;
         }

         /* COPYRIGHT: This style formats the text of the copyright statement at the bottom of the page */
         div.refsect3 {
             font: normal 11px verdana, sans-serif;
             margin-top: 50px;
             margin-bottom: 20px;
             padding-top: 0;
             padding-bottom: 0;
         }

 </style>
     <title>Attributes of Types</title>
     <meta name="generator" content="DocBook XSL Stylesheets V1.79.1" />
     <meta name="keywords" content="Attributes of Types" />
   </head>
   <body>
     <div class="refentry">
       <a id="id-1"></a>
       <div class="titlepage"></div>
       <div xmlns="" class="refnamediv">
         <a xmlns="http://www.w3.org/1999/xhtml" id="AttributesofTypes"></a>
         <h1>Attributes of Types</h1>
         <p>
             Attributes of Types.
         </p>
       </div>
       <div class="refsect2">
         <a id="synopsis"></a>
         <h3>
         </h3>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">
 __attribute__ ((aligned))
 __attribute__ ((aligned (<span class="emphasis"><em>n</em></span>)))
 __attribute__ ((packed))
                         </td>
               </tr>
             </tbody>
           </table>
         </div>
       </div>
       <div class="refsect1">
         <a id="description"></a>
         <h2>Description</h2>
         <p>
           The keyword <code class="constant">__attribute__</code> allows you to specify special attributes
           of <code class="code">enum</code>, <code class="code">struct</code> and <code class="code">union</code> types when you
           define such types. This keyword is followed by an attribute specification inside
           double parentheses. Two attributes are currently defined for types: aligned, and packed.
         </p>
         <p>
           You may specify type attributes in an <code class="code">enum</code>, <code class="code">struct</code>,
           or <code class="code">union</code> type declaration or definition, or for other types in a
           <code class="code">typedef</code> declaration.
         </p>
         <p>
           For an <code class="code">enum</code>, <code class="code">struct</code>, or <code class="code">union</code> type, you
           may specify attributes either between the <code class="code">enum</code>, <code class="code">struct</code>
           or <code class="code">union</code> tag and the name of the type, or just past the closing curly
           brace of the <span class="emphasis"><em>definition</em></span>. The former syntax is preferred.
         </p>
       </div>
       <div class="refsect2">
         <a id="aligned"></a>
         <h3>aligned (<code class="varname">alignment</code>)</h3>
         <p>
           This attribute specifies a minimum alignment (in bytes) for variables of the specified
           type. For example, the declarations:
         </p>
         <p>
         </p>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">    <code class="code">struct S { short f[3]; } __attribute__ ((aligned (8)));
     typedef int more_aligned_int __attribute__ ((aligned (8)));</code></td>
               </tr>
             </tbody>
           </table>
         </div>
         <p>
     </p>
         <p>
       force the compiler to insure (as far as it can) that each variable whose type is
       <code class="code">struct S</code> or <code class="code">more_aligned_int</code> will be allocated and aligned
       <span class="emphasis"><em>at least</em></span> on a 8-byte boundary.
     </p>
         <p>
       Note that the alignment of any given <code class="code">struct</code> or <code class="code">union</code> type
       is required by the ISO C standard to be at least a perfect multiple of the lowest
       common multiple of the alignments of all of the members of the <code class="code">struct</code>
       or <code class="code">union</code> in question and must also be a power of two. This means that
       you <span class="emphasis"><em>can</em></span> effectively adjust the alignment of a <code class="code">struct</code>
       or <code class="code">union</code> type by attaching an aligned attribute to any one of the members
       of such a type, but the notation illustrated in the example above is a more obvious,
       intuitive, and readable way to request the compiler to adjust the alignment of an entire
       <code class="code">struct</code> or <code class="code">union</code> type.
     </p>
         <p>
       As in the preceding example, you can explicitly specify the alignment (in bytes) that
       you wish the compiler to use for a given <code class="code">struct</code> or <code class="code">union</code>
       type. Alternatively, you can leave out the alignment factor and just ask the compiler
       to align a type to the maximum useful alignment for the target machine you are compiling
       for. For example, you could write:
     </p>
         <p>
          </p>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">    <code class="code">struct S { short f[3]; } __attribute__ ((aligned));</code></td>
               </tr>
             </tbody>
           </table>
         </div>
         <p>
     </p>
         <p>
       Whenever you leave out the alignment factor in an <code class="code">aligned</code> attribute
       specification, the compiler automatically sets the alignment for the type to the largest
       alignment which is ever used for any data type on the target machine you are compiling
       for. In the example above, the size of each <code class="code">short</code> is 2 bytes, and therefore
       the size of the entire <code class="code">struct S</code> type is 6 bytes. The smallest power of two
       which is greater than or equal to that is 8, so the compiler sets the alignment for the
       entire <code class="code">struct S</code> type to 8 bytes.
     </p>
         <p>
       Note that the effectiveness of aligned attributes may be limited by inherent limitations
       of the OpenCL device and compiler. For some devices, the OpenCL compiler may only be
       able to arrange for variables to be aligned up to a certain maximum alignment. If the
       OpenCL compiler is only able to align variables up to a maximum of 8 byte alignment, then
       specifying <code class="code">aligned(16)</code> in an <code class="code">__attribute__</code> will still only provide
       you with 8 byte alignment. See your platform-specific documentation for further information.
     </p>
         <p>
       The <code class="code">aligned</code> attribute can only increase the alignment; but you can decrease
       it by specifying <code class="code">packed</code> as well. See below.
     </p>
       </div>
       <div class="refsect2">
         <a id="packed"></a>
         <h3>packed</h3>
         <p>
       The <code class="constant">packed</code> attribute, attached to the <code class="code">struct</code>
       or <code class="code">union</code> type definition, specifies that each member of the structure or
       union is placed to minimize the memory required. When attached to an <code class="code">enum</code>
       definition, it indicates that the smallest integral type should be used.
     </p>
         <p>
       Specifying this attribute for <code class="code">struct</code> and <code class="code">union</code> types is equivalent
       to specifying the <code class="code">packed</code> attribute on each of the structure or union members.
     </p>
         <p>
       In the following example <code class="code">struct my_packed_struct</code>'s members are packed closely
       together, but the internal layout of its <code class="code">s</code> member is not packed. To do that,
       <code class="code">struct my_unpacked_struct</code> would need to be packed, too.
     </p>
         <p>
          </p>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">    <code class="code">struct my_unpacked_struct
     {
         char c;
         int i;
     };

     struct __attribute__ ((packed)) my_packed_struct
     {
         char c;
         int i;
         struct my_unpacked_struct s;
     };</code></td>
               </tr>
             </tbody>
           </table>
         </div>
         <p>
     </p>
         <p>
       You may only specify this attribute on the definition of a <code class="code">enum</code>,
       <code class="code">struct</code>, or <code class="code">union</code>, not on a <code class="code">typedef</code> which does not
       also define the enumerated type, structure or union.
     </p>
       </div>
       <div class="refsect1">
         <a id="specification"></a>
         <h2>Specification</h2>
         <p>
             <img src="pdficon_small1.gif" />

             <a href="https://www.khronos.org/registry/cl/specs/opencl-2.1-openclc.pdf#page=57" target="OpenCL Spec">OpenCL Specification</a>
         </p>
       </div>
       <div class="refsect1">
         <a id="seealso"></a>
         <h2>Also see</h2>
         <p>
             <a class="citerefentry" href="attribute.html"><span class="citerefentry"><span class="refentrytitle">__attribute__</span></span></a>,
             <a class="citerefentry" href="attributes-blocksAndControlFlow.html"><span class="citerefentry"><span class="refentrytitle">Blocks and Control-Flow Statement Attributes</span></span></a>,
             <a class="citerefentry" href="attributes-variables.html"><span class="citerefentry"><span class="refentrytitle">Variable Attributes</span></span></a>,
             <a class="citerefentry" href="attributes-loopUnroll.html"><span class="citerefentry"><span class="refentrytitle">Loop Unroll Attributes</span></span></a>,
             <a class="citerefentry" href="qualifiers.html"><span class="citerefentry"><span class="refentrytitle">Qualifiers</span></span></a>
         </p>
       </div>
       <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2015 The Khronos Group Inc.
 Permission is hereby granted, free of charge, to any person obtaining a
 copy of this software and/or associated documentation files (the
 "Materials"), to deal in the Materials without restriction, including
 without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Materials, and to
 permit persons to whom the Materials are furnished to do so, subject to
 the condition that this copyright notice and permission notice shall be included
 in all copies or substantial portions of the Materials.
 </div>
     </div>
   </body>
 </html>
	<?xml version="1.0" encoding="UTF-8"?>
	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd">
	<!-- saved from url=(0013)about:internet -->
	<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" xmlns:xlink="http://www.w3.org/1999/xlink" pref:renderer="mathplayer-dl">
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
	<style xmlns="" type="text/css">
	/* This style sets a margin around the entire page */
	html, body {
	margin: 10px;
	}

	p {
	font: normal 16px verdana, sans-serif;
	margin: 0;
	padding-bottom:12px;
	}

	h1 {
	font: bold 25px verdana, sans-serif;
	margin-top: 0;
	margin-bottom: 3px;
	padding-top: 0;
	padding-bottom: 0;
	}

	h2 {
	font: bold 19px verdana, sans-serif;
	margin-top: 28px;
	margin-bottom: 3px;
	padding-top: 0;
	padding-bottom: 0;
	}

	h3 {
	font: bold 19px verdana, sans-serif !important;
	margin-top: 28px;
	margin-bottom: 3px;
	padding-top: 0;
	padding-bottom: 0;
	}

	li {
	font: normal 16px verdana, sans-serif;
	margin-top: 0;
	margin-bottom: 18px;
	padding-top: 0;
	padding-bottom: 0;
	}

	.pdparam {
	font: italic 16px verdana, sans-serif;
	}

	.term {
	font: italic 16px verdana, sans-serif;
	font-weight: normal;
	}

	.type {
	font: normal 16px verdana, sans-serif !important;
	}

	.parameter {
	font-style: italic;
	}

	a:link, a:visited {
	color: blue;
	text-decoration: none;
	font: normal 16px;
	}

	a:hover {
	background-color: #FFFF99;
	font: normal 16px;
	}

	div.funcsynopsis {
	text-align: left;
	background-color: #e6e6e6;
	font: normal 16px verdana, sans-serif;
	padding-top: 10px;
	padding-bottom: 10px;
	}

	div.funcsynopsis table {
	border-collapse: separate;
	font: normal 16px verdana, sans-serif;
	}

	div.funcsynopsis td {
	background-color: #e6e6e6;
	border: 0 solid #000;
	padding: 1px;
	font: normal 16px verdana, sans-serif;
	}

	div.refsect1 {
	font-family: verdana, sans-serif;
	font-size: 16px;
	}

	code.constant {
	font: normal 16px courier new, monospace !important;
	}

	span.errorname {
	font: normal 16px verdana, sans-serif !important;
	}

	code.function {
	font: bold 16px verdana, sans-serif !important;
	}

	b.fsfunc {
	font: bold 16px verdana, sans-serif !important;
	}

	code.varname {
	font: italic 16px verdana, sans-serif;
	}

	code.replaceable {
	font: italic 16px courier new, monospace;
	}

	code.funcdef {
	font: normal 16px verdana, sans-serif !important;
	}

	.citerefentry {
	font: normal 16px verdana, sans-serif !important;
	}

	.parameter {
	font-style: italic;
	}

	code.fsfunc {
	font: normal 16px verdana, sans-serif !important;
	}

	/* PARAMETER: This style controls spacing between the terms in Parameter section */
	dt {
	margin-top: 15px;
	}

	/* TABLES: These styles apply to all tables OTHER than the Synopsis and Example tables */
	div.refsect1 table {
	width: 100%;
	margin-top: 10px;
	background-color: #FFF;
	border-collapse: collapse;
	border-color: #000;
	border-width: 1px;
	font: normal 16px verdana, sans-serif;
	}

	div.refsect1 th {
	border-collapse: collapse;
	border-color: #000;
	border-width: 1px;
	font: bold 16px verdana, sans-serif;
	}

	div.refsect1 td {
	background-color: #FFF;
	padding: 5px;
	vertical-align: text-top;
	border-collapse: collapse;
	border-color: #000;
	border-width: 1px;
	font: normal 16px verdana, sans-serif;
	}

	div.refsect1 p{
	font: normal 16px verdana, sans-serif;
	margin-top: 8px;
	margin-bottom: 8px;
	padding-top: 0;
	padding-bottom: 0;
	}


	/* EXAMPLE: These styles apply only to the Example section */
	div.refsect2 {
	font: normal 16px courier new, monospace !important;
	}

	div.refsect2 table {
	margin-top: 0;
	background-color: #e6e6e6;
	width: 100%;
	border: 0 solid #000;
	padding: 2px;
	font: normal 16px courier new, monospace !important;
	}

	div.refsect2 td {
	background-color: #e6e6e6;
	font: normal 16px courier new, monospace !important;
	white-space:pre;
	}

	/* COPYRIGHT: This style formats the text of the copyright statement at the bottom of the page */
	div.refsect3 {
	font: normal 11px verdana, sans-serif;
	margin-top: 50px;
	margin-bottom: 20px;
	padding-top: 0;
	padding-bottom: 0;
	}

	</style>
	<title>Attributes of Types</title>
	<meta name="generator" content="DocBook XSL Stylesheets V1.79.1" />
	<meta name="keywords" content="Attributes of Types" />
	</head>
	<body>
	<div class="refentry">
	<a id="id-1"></a>
	<div class="titlepage"></div>
	<div xmlns="" class="refnamediv">
	<a xmlns="http://www.w3.org/1999/xhtml" id="AttributesofTypes"></a>
	<h1>Attributes of Types</h1>
	<p>
	Attributes of Types.
	</p>
	</div>
	<div class="refsect2">
	<a id="synopsis"></a>
	<h3>
	</h3>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left">
	__attribute__ ((aligned))
	__attribute__ ((aligned (<span class="emphasis"><em>n</em></span>)))
	__attribute__ ((packed))
	</td>
	</tr>
	</tbody>
	</table>
	</div>
	</div>
	<div class="refsect1">
	<a id="description"></a>
	<h2>Description</h2>
	<p>
	The keyword <code class="constant">__attribute__</code> allows you to specify special attributes
	of <code class="code">enum</code>, <code class="code">struct</code> and <code class="code">union</code> types when you
	define such types. This keyword is followed by an attribute specification inside
	double parentheses. Two attributes are currently defined for types: aligned, and packed.
	</p>
	<p>
	You may specify type attributes in an <code class="code">enum</code>, <code class="code">struct</code>,
	or <code class="code">union</code> type declaration or definition, or for other types in a
	<code class="code">typedef</code> declaration.
	</p>
	<p>
	For an <code class="code">enum</code>, <code class="code">struct</code>, or <code class="code">union</code> type, you
	may specify attributes either between the <code class="code">enum</code>, <code class="code">struct</code>
	or <code class="code">union</code> tag and the name of the type, or just past the closing curly
	brace of the <span class="emphasis"><em>definition</em></span>. The former syntax is preferred.
	</p>
	</div>
	<div class="refsect2">
	<a id="aligned"></a>
	<h3>aligned (<code class="varname">alignment</code>)</h3>
	<p>
	This attribute specifies a minimum alignment (in bytes) for variables of the specified
	type. For example, the declarations:
	</p>
	<p>
	</p>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left"> <code class="code">struct S { short f[3]; } __attribute__ ((aligned (8)));
	typedef int more_aligned_int __attribute__ ((aligned (8)));</code></td>
	</tr>
	</tbody>
	</table>
	</div>
	<p>
	</p>
	<p>
	force the compiler to insure (as far as it can) that each variable whose type is
	<code class="code">struct S</code> or <code class="code">more_aligned_int</code> will be allocated and aligned
	<span class="emphasis"><em>at least</em></span> on a 8-byte boundary.
	</p>
	<p>
	Note that the alignment of any given <code class="code">struct</code> or <code class="code">union</code> type
	is required by the ISO C standard to be at least a perfect multiple of the lowest
	common multiple of the alignments of all of the members of the <code class="code">struct</code>
	or <code class="code">union</code> in question and must also be a power of two. This means that
	you <span class="emphasis"><em>can</em></span> effectively adjust the alignment of a <code class="code">struct</code>
	or <code class="code">union</code> type by attaching an aligned attribute to any one of the members
	of such a type, but the notation illustrated in the example above is a more obvious,
	intuitive, and readable way to request the compiler to adjust the alignment of an entire
	<code class="code">struct</code> or <code class="code">union</code> type.
	</p>
	<p>
	As in the preceding example, you can explicitly specify the alignment (in bytes) that
	you wish the compiler to use for a given <code class="code">struct</code> or <code class="code">union</code>
	type. Alternatively, you can leave out the alignment factor and just ask the compiler
	to align a type to the maximum useful alignment for the target machine you are compiling
	for. For example, you could write:
	</p>
	<p>
	</p>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left"> <code class="code">struct S { short f[3]; } __attribute__ ((aligned));</code></td>
	</tr>
	</tbody>
	</table>
	</div>
	<p>
	</p>
	<p>
	Whenever you leave out the alignment factor in an <code class="code">aligned</code> attribute
	specification, the compiler automatically sets the alignment for the type to the largest
	alignment which is ever used for any data type on the target machine you are compiling
	for. In the example above, the size of each <code class="code">short</code> is 2 bytes, and therefore
	the size of the entire <code class="code">struct S</code> type is 6 bytes. The smallest power of two
	which is greater than or equal to that is 8, so the compiler sets the alignment for the
	entire <code class="code">struct S</code> type to 8 bytes.
	</p>
	<p>
	Note that the effectiveness of aligned attributes may be limited by inherent limitations
	of the OpenCL device and compiler. For some devices, the OpenCL compiler may only be
	able to arrange for variables to be aligned up to a certain maximum alignment. If the
	OpenCL compiler is only able to align variables up to a maximum of 8 byte alignment, then
	specifying <code class="code">aligned(16)</code> in an <code class="code">__attribute__</code> will still only provide
	you with 8 byte alignment. See your platform-specific documentation for further information.
	</p>
	<p>
	The <code class="code">aligned</code> attribute can only increase the alignment; but you can decrease
	it by specifying <code class="code">packed</code> as well. See below.
	</p>
	</div>
	<div class="refsect2">
	<a id="packed"></a>
	<h3>packed</h3>
	<p>
	The <code class="constant">packed</code> attribute, attached to the <code class="code">struct</code>
	or <code class="code">union</code> type definition, specifies that each member of the structure or
	union is placed to minimize the memory required. When attached to an <code class="code">enum</code>
	definition, it indicates that the smallest integral type should be used.
	</p>
	<p>
	Specifying this attribute for <code class="code">struct</code> and <code class="code">union</code> types is equivalent
	to specifying the <code class="code">packed</code> attribute on each of the structure or union members.
	</p>
	<p>
	In the following example <code class="code">struct my_packed_struct</code>'s members are packed closely
	together, but the internal layout of its <code class="code">s</code> member is not packed. To do that,
	<code class="code">struct my_unpacked_struct</code> would need to be packed, too.
	</p>
	<p>
	</p>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left"> <code class="code">struct my_unpacked_struct
	{
	char c;
	int i;
	};

	struct __attribute__ ((packed)) my_packed_struct
	{
	char c;
	int i;
	struct my_unpacked_struct s;
	};</code></td>
	</tr>
	</tbody>
	</table>
	</div>
	<p>
	</p>
	<p>
	You may only specify this attribute on the definition of a <code class="code">enum</code>,
	<code class="code">struct</code>, or <code class="code">union</code>, not on a <code class="code">typedef</code> which does not
	also define the enumerated type, structure or union.
	</p>
	</div>
	<div class="refsect1">
	<a id="specification"></a>
	<h2>Specification</h2>
	<p>
	<img src="pdficon_small1.gif" />

	<a href="https://www.khronos.org/registry/cl/specs/opencl-2.1-openclc.pdf#page=57" target="OpenCL Spec">OpenCL Specification</a>
	</p>
	</div>
	<div class="refsect1">
	<a id="seealso"></a>
	<h2>Also see</h2>
	<p>
	<a class="citerefentry" href="attribute.html"><span class="citerefentry"><span class="refentrytitle">__attribute__</span></span></a>,
	<a class="citerefentry" href="attributes-blocksAndControlFlow.html"><span class="citerefentry"><span class="refentrytitle">Blocks and Control-Flow Statement Attributes</span></span></a>,
	<a class="citerefentry" href="attributes-variables.html"><span class="citerefentry"><span class="refentrytitle">Variable Attributes</span></span></a>,
	<a class="citerefentry" href="attributes-loopUnroll.html"><span class="citerefentry"><span class="refentrytitle">Loop Unroll Attributes</span></span></a>,
	<a class="citerefentry" href="qualifiers.html"><span class="citerefentry"><span class="refentrytitle">Qualifiers</span></span></a>
	</p>
	</div>
	<div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2015 The Khronos Group Inc.
	Permission is hereby granted, free of charge, to any person obtaining a
	copy of this software and/or associated documentation files (the
	"Materials"), to deal in the Materials without restriction, including
	without limitation the rights to use, copy, modify, merge, publish,
	distribute, sublicense, and/or sell copies of the Materials, and to
	permit persons to whom the Materials are furnished to do so, subject to
	the condition that this copyright notice and permission notice shall be included
	in all copies or substantial portions of the Materials.
	</div>
	</div>
	</body>
	</html>