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| <title>restrictions</title> |
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| <div class="refentry"> |
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| <div class="titlepage"></div> |
| <div xmlns="" class="refnamediv"> |
| <a xmlns="http://www.w3.org/1999/xhtml" id="restrictionsref"></a> |
| <h1>Restrictions</h1> |
| <p> </p> |
| </div> |
| <div class="refsect1"> |
| <a id="restrictions"></a> |
| <h2></h2> |
| <div class="itemizedlist"> |
| <ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>The use of pointers is somewhat restricted. The following rules apply:</p> |
| <div class="itemizedlist"> |
| <ul class="itemizedlist" style="list-style-type: opencircle; "> |
| <li class="listitem" style="list-style-type: circle"> |
| <p> |
| Arguments to kernel |
| functions declared in a program that are pointers must be declared with the |
| <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>, or |
| <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a> |
| qualifier. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: circle"> |
| <p> |
| A pointer declared with the |
| <a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a> |
| qualifier can only be assigned to a pointer declared with the __constant qualifier. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: circle"> |
| <p>Pointers to functions are not allowed.</p> |
| </li> |
| </ul> |
| </div> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| An image type ( |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image3d_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_array_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_buffer_t</span></span></a>, or |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_array_t</span></span></a>) |
| can only be used as the type of a function argument. An image function |
| argument cannot be modified. Elements of an image can only be accessed |
| using the <a class="citerefentry" href="imageFunctions.html"><span class="citerefentry"><span class="refentrytitle">Built-in Image |
| Functions</span></span></a>. |
| </p> |
| <p> |
| An image type cannot be used to declare a variable, a structure or |
| union field, an array of images, a pointer to an image, or the return |
| type of a function. An image type cannot be used with the |
| <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a>, |
| <a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</span></span></a>, |
| <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a> and |
| <a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a> |
| address space qualifiers. |
| </p> |
| <p> |
| The sampler type |
| (<a class="citerefentry" href="sampler_t.html"><span class="citerefentry"><span class="refentrytitle">sampler_t</span></span></a>) can only be |
| used as the type of a function argument or a variable declared in the program scope |
| or the outermost scope of a kernel function. The behavior of a sampler variable |
| declared in a non-outermost scope of a kernel function is implementation-defined. A |
| sampler argument or variable cannot be modified. |
| </p> |
| <p> |
| The sampler type cannot be used to declare a structure or union field, an array of |
| samplers, a pointer to a sampler, or the return type of a function. The sampler type |
| cannot be used with the |
| <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a> and |
| <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a> |
| address space qualifiers. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Bit-fields struct members are currently not supported.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Variable length arrays and structures with |
| flexible (or unsized) arrays are not supported.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Variadic macros and functions with the exception of |
| <a class="citerefentry" href="printfFunction.html"><span class="citerefentry"><span class="refentrytitle">printf</span></span></a> and |
| <a class="citerefentry" href="enqueue_kernel.html"><span class="citerefentry"><span class="refentrytitle">enqueue_kernel</span></span></a> |
| are not supported.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| The library functions defined in the C99 standard headers <code class="code">assert.h</code>, |
| <code class="code">ctype.h</code>, <code class="code">complex.h</code>, <code class="code">errno.h</code>, |
| <code class="code">fenv.h</code>, <code class="code">float.h</code>, <code class="code">inttypes.h</code>, |
| <code class="code">limits.h</code>, <code class="code">locale.h</code>, <code class="code">setjmp.h</code>, |
| <code class="code">signal.h</code>, <code class="code">stdarg.h</code>, <code class="code">stdio.h</code>, |
| <code class="code">stdlib.h</code>, <code class="code">string.h</code>, <code class="code">tgmath.h</code>, |
| <code class="code">time.h</code>, <code class="code">wchar.h</code>, and <code class="code">wctype.h</code> are not |
| available and cannot be included by a program. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| The <code class="code">auto</code> and <code class="code">register</code> |
| storage-class specifiers are not supported. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Recursion is not supported.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| The return type of a kernel function must be <span class="type">void</span>. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| Arguments to kernel functions in a program cannot be declared with the built-in |
| scalar types <span class="type">bool</span>, <span class="type">half</span>, <span class="type">size_t</span>, |
| <span class="type">ptrdiff_t</span>, <span class="type">intptr_t</span>, and <span class="type">uintptr_t</span>, or |
| a struct and/or union that contain fields declared to be one of these built-in |
| scalar types. The size in bytes of these types except <span class="type">half</span> are |
| implementation-defined and in addition can also be different for the OpenCL device |
| and the host processor making it difficult to allocate buffer objects to be passed |
| as arguments to a kernel declared as pointer to these types. <span class="type">half</span> is |
| not supported as <span class="type">half</span> can be used as a storage format only (unless the |
| <a class="citerefentry" href="cl_khr_fp16.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_fp16</span></span></a> extension is |
| supported) and is not a data type on which floating-point arithmetic can be performed. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Whether or not irreducible control flow is illegal is implementation defined.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| The type qualifiers <code class="code">const</code>, <code class="code">restrict</code> |
| and <code class="code">volatile</code> as defined by the C99 |
| specification are supported. These qualifiers cannot be used with |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image3d_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_array_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_depth_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_array_depth_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_t</span></span></a>, |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_buffer_t</span></span></a> and |
| <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_array_t</span></span></a> |
| types. Types other than pointer types shall not use the |
| <code class="code">restrict</code> qualifier. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| The event type |
| (<a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">event_t</span></span></a>) |
| cannot be used as the type of a kernel function argument. |
| The event type cannot be used to declare a program scope variable. The event type |
| cannot be used to declare a structure or union field. The event type cannot be used with the |
| <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a>, |
| <a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a> and |
| <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a> |
| address space qualifiers. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| The <span class="type">clk_event_t</span>, <span class="type">ndrange_t</span> and |
| <span class="type">reserve_id_t</span> types cannot be used as arguments to |
| kernel functions that get enqueued from the host. The |
| <span class="type">clk_event_t</span> and <span class="type">reserve_id_t</span> types |
| cannot be declared in program scope. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| The behavior of applying the <code class="code">sizeof</code> operator |
| to the <span class="type">queue_t</span>, <span class="type">clk_event_t</span>, |
| <span class="type">ndrange_t</span> and <span class="type">reserve_id_t</span> |
| types is implementation-defined. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| Kernels enqueued by the host must continue to have |
| their arguments that are a pointer to |
| a type declared to point to a named address space. |
| </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p> |
| A function in an OpenCL program cannot be called <code class="code">main</code>. |
| </p> |
| </li> |
| </ul> |
| </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=51" target="OpenCL Spec">OpenCL Specification</a> |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="seealso"></a> |
| <h2>Also see</h2> |
| <p> |
| <a class="citerefentry" href="imageFunctions.html"><span class="citerefentry"><span class="refentrytitle">Image Functions</span></span></a>, |
| <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">Function Qualifiers</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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