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| <title>restrictions</title> |
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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 <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> functions declared in a program that are pointers must be declared with the __global, __constant or __local 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>, <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a>, or <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a> qualifier can |
| only be assigned to a pointer declared with the __constant, __local, or __global qualifier respectively.</p> |
| </li> |
| <li class="listitem" style="list-style-type: circle"> |
| <p>Pointers to functions are not allowed.</p> |
| </li> |
| <li class="listitem" style="list-style-type: circle"> |
| <p>Arguments to <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> functions in a program cannot be declared as a pointer to a pointer(s). Variables inside a function or arguments to non __kernel functions in a |
| program can be declared as a pointer to a pointer(s).</p> |
| </li> |
| </ul> |
| </div> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Variables that are declared to be of type <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_t</span></span></a> or <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image3d_t</span></span></a> refer to image |
| memory objects. These can only be specified as arguments to a function. Elements of an |
| image cannot be directly accessed. Specific built-in <a class="citerefentry" href="imageFunctions.html"><span class="citerefentry"><span class="refentrytitle">image read and write functions</span></span></a> are provided to read from |
| and write to any location in the image. Pointers to image2d_t or image3d_t are not allowed. |
| image2d_t or image3d_t data types cannot be declared in a struct. image2d_t and |
| image3d_t cannot be used to declare local variables or as the return type of a function. |
| An image2d_t or image3d_t argument to a function cannot be modified.</p> |
| <p>Samplers cannot be declared as arrays, pointers, or be used as the type for local variables |
| inside a function or as the return value of a function defined in a program. Samplers |
| cannot be passed as arguments to functions called by a <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> function. A sampler |
| argument to a __kernel function cannot be modified. </p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Bit-fields 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 are not supported.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>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">extern</code>, <code class="code">static</code>, <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>Predefined identifiers 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 function using the <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> qualifier can only have return type <span class="type">void</span> in the source code.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Arguments to <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> 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>. 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 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>Built-in types that are less than 32-bits in size i.e. <span class="type">char</span>, <span class="type">uchar</span>, <span class="type">char2</span>, <span class="type">uchar2</span>, <span class="type">short</span>, <span class="type">ushort</span>, and <span class="type">half</span> have the following restriction:</p> |
| <p>Writes to a pointer (or arrays) of type <span class="type">char</span>, <span class="type">uchar</span>, <span class="type">char2</span>, <span class="type">uchar2</span>, <span class="type">short</span>, <span class="type">ushort</span>, and <span class="type">half</span> or to elements of a struct that are of type <span class="type">char</span>, <span class="type">uchar</span>, <span class="type">char2</span>, <span class="type">uchar2</span>, <span class="type">short</span>, and <span class="type">ushort</span> are not supported. </p> |
| <p>The kernel example below shows what memory operations are not supported on built-in types less than 32-bits in size.</p> |
| <div class="literallayout"> |
| <p> |
| <code class="code"><br /> |
| kernel void<br /> |
| do_proc (__global char *pA, short b,<br /> |
| __global short *pB)<br /> |
| {<br /> |
| char x[100];<br /> |
| __private char *px = x;<br /> |
| int id = (int)get_global_id(0);<br /> |
| short f;<br /> |
| f = pB[id] + b; // is allowed<br /> |
| px[1] = pA[1]; // error. px cannot be written.<br /> |
| pB[id] = b; // error. pB cannot be written<br /> |
| }</code> |
| </p> |
| </div> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Arguments to <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> functions in a program cannot be declared to be of type <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">event_t</span></span></a>.</p> |
| </li> |
| <li class="listitem" style="list-style-type: disc"> |
| <p>Elements of a struct or union must belong to the same address space. Declaring a struct or union whose elements are in different address spaces is illegal.</p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="specification"></a> |
| <h2>Specification</h2> |
| <p><img src="pdficon_small1.gif" /> |
| <a href="http://www.khronos.org/registry/cl/specs/opencl-1.0.pdf#page=157" 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> |
| </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> |
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