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<h4 class="subsection">6.58.26 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><spu_intrinsics.h></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 class="noindent">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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