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<h4 class="subsection">6.52.15 SPU Built-in Functions</h4>

<p>GCC provides extensions for the SPU processor as described in the
Sony/Toshiba/IBM SPU Language Extensions Specification, which can be
found at <a href="http://cell.scei.co.jp/">http://cell.scei.co.jp/</a> or
<a href="http://www.ibm.com/developerworks/power/cell/">http://www.ibm.com/developerworks/power/cell/</a>.  GCC's
implementation differs in several ways.

     <ul>
<li>The optional extension of specifying vector constants in parentheses is
not supported.

     <li>A vector initializer requires no cast if the vector constant is of the
same type as the variable it is initializing.

     <li>If <code>signed</code> or <code>unsigned</code> is omitted, the signedness of the
vector type is the default signedness of the base type.  The default
varies depending on the operating system, so a portable program should
always specify the signedness.

     <li>By default, the keyword <code>__vector</code> is added. The macro
<code>vector</code> is defined in <code>&lt;spu_intrinsics.h&gt;</code> and can be
undefined.

     <li>GCC allows using a <code>typedef</code> name as the type specifier for a
vector type.

     <li>For C, overloaded functions are implemented with macros so the following
does not work:

     <pre class="smallexample">            spu_add ((vector signed int){1, 2, 3, 4}, foo);
</pre>
     <p>Since <code>spu_add</code> is a macro, the vector constant in the example
is treated as four separate arguments.  Wrap the entire argument in
parentheses for this to work.

     <li>The extended version of <code>__builtin_expect</code> is not supported.

 </ul>

 <p><em>Note:</em> Only the interface described in the aforementioned
specification is supported. Internally, GCC uses built-in functions to
implement the required functionality, but these are not supported and
are subject to change without notice.

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