xslt_create()

[ruben21]

Hola, intento transformar un archivo xml usando php y xsl, pero me sale el siguiente error: Call to undefined function xslt_create()

el código es el siguiente:
<?
// First we declare the XML and XSL files and allocate them to variables
$xml_file = "link al archivo";
$xsl_file = "ruben.xsl";
// Then we allocate a new XSLT processor
$xh = xslt_create();
$fileBase = 'file://' . getcwd () . '/';
xslt_set_base ( $xh, $fileBase );
// Then PHP process the XML document using the given XSLT transformation
$result = xslt_process($xh, $xml_file, $xsl_file);
if (!$result) {
// As usually sometimes something might go wrong, then we need to show that error has occurred
echo 'XSLT processing error: ' .xslt_error($xh) ;
}
else {
// If there is no error then show the resulting HTML based on XSLT
echo $result;
}
// In the end we destroy the XSLT processor
xslt_free($xh);
?>

Significa esto que me falta alguna dll??