php16进制转二进制流

</pre><pre name="code" class="php">function hex2bin($str){
	$len = strlen($str)/2;
	$re = '';
	for($i=0;$i<$len;$i++){
		$pos = $i*2;
		$re .= chr(hexdec(substr($str,$pos,1))<<4) | chr(hexdec(substr($str,$pos+1,1)));
	}
	return $re;
}