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| <title>genericAddressSpace</title> |
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| </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="genericAddressSpace"></a> |
| <h1>generic</h1> |
| <p> |
| Generic Address Space. |
| </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"> |
| __generic (unnamed address space) |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="description"></a> |
| <h2>Description</h2> |
| <p> |
| Generic address space (glossary): An address space that include the private, local, and global address |
| spaces available to a device. The generic address space supports conversion of pointers to and |
| from private, local and global address spaces, and hence lets a programmer write a single |
| function that at compile time can take arguments from any of the three named address spaces. |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="notes"></a> |
| <h2>Notes</h2> |
| <p> |
| Programmers often need functions callable from kernels where the pointers manipulated by those |
| functions can point to multiple named address spaces. This saves a programmer from the error- |
| prone and wasteful practice of creating multiple copies of functions; one for each named address |
| space. Therefore the global, local and private address spaces belong to a single |
| <span class="emphasis"><em>generic address space</em></span>. |
| This is closely modeled after the concept of a generic address space used in the embedded |
| C standard (ISO/IEC 9899:1999). Since they all belong to a single generic address space, the |
| following properties are supported for pointers to named address spaces in device memory: |
| </p> |
| <p> |
| The following rules apply when using pointers that point to the generic address space: |
| </p> |
| <div class="itemizedlist"> |
| <ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| <p> |
| A pointer that points to the <code class="function">global</code>, |
| <code class="function">local</code> or <code class="function">private</code> address space can be |
| implicitly converted to a pointer to the unnamed |
| generic address space but not vice-versa. |
| </p> |
| </li> |
| <li class="listitem"> |
| <p> |
| Pointer casts can be used to cast a pointer that points to the |
| <code class="function">global</code>, <code class="function">local</code> |
| or <code class="function">private</code> space to |
| the unnamed generic addresss space and vice-versa. |
| </p> |
| </li> |
| <li class="listitem"> |
| <p> |
| A pointer that points to the <code class="function">constant</code> |
| address space cannot be cast or implicitly |
| converted to the generic address space. |
| </p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| <div class="refsect2"> |
| <a id="example1"></a> |
| <h3> |
| Example |
| </h3> |
| <p> |
| This is the canonical example. In this example, function |
| <code class="function">foo</code>() is declared with an argument that |
| is a pointer with no address space qualifier. |
| </p> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td align="left"> |
| void foo(int *a) |
| { |
| *a = *a + 2; |
| } |
| |
| kernel void k1(local int *a) |
| { |
| … |
| foo(a); |
| … |
| } |
| kernel void k2(global int *a) |
| { |
| … |
| foo(a); |
| … |
| } |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <p> |
| In the example below, <code class="varname">var</code> is in the unnamed |
| generic address space which gets mapped to the |
| <code class="function">global</code> or <code class="function">local</code> |
| address space depending on the result of the conditional expression. |
| </p> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td align="left"> |
| kernel void bar(global int *g, local int *l) |
| { |
| int *var; |
| if (is_even(get_global_id(0)) |
| var = g; |
| else |
| var = l; |
| *var = 42; |
| … |
| } |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <p> |
| The example below is an example with one unnamed |
| generic address space pointer with multiple |
| named address space assignments. |
| </p> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td align="left"> |
| int *ptr; |
| global int g; |
| ptr = &g; // legal |
| |
| local int l; |
| ptr = &l; // legal |
| |
| private int p; |
| ptr = &p; // legal |
| |
| constant int c; |
| ptr = &c; // illegal |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <p> |
| The example below is an example with one unnamed |
| generic address space pointer being |
| assigned to point to several named address spaces. |
| </p> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td align="left"> |
| global int * gp; |
| local int *lp; |
| private int *pp; |
| |
| int *p; |
| p = gp; // legal |
| p = lp; // legal |
| p = pp; // legal |
| |
| // it is illegal to convert from a generic pointer |
| // to an explicit address space pointer without a cast: |
| gp = p; // compile-time error |
| lp = p; // compile-time error |
| pp = p; // compile-time error |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </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=38" target="OpenCL Spec">OpenCL Specification</a> |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="seealso"></a> |
| <h2>Also see</h2> |
| <p> |
| <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a>, |
| <a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a>, |
| <a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</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. |
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