PHP Decode

<?  $d=''; 
$key = ""; 
if (isset($_POST['o_o'])) 
  $key = $_POST['o_o']; 
if (isset($_POST['hint'])) 
  $d = "www.p01.org"; 
if (isset($_POST['t'])) { 
  if ($_POST['t'] == 'c') { 
    $d = base64_decode('SDcGHg1feVUIEhsbDxFhIBIYFQY+VwMWTyAcOhEYAw4VLVBaXRsKADMXTWxrSH4ZS1IiAgA3GxYUQVMvBFdVTysRMQAaQUxZYTlsTg0MECZSGgVcNn9AAwobXgcxHQRBAxMcWwodHV5EfxQfAAYrMlsCQlJBAAAAAAAAAAAAAAAAAFZhf3ldEQY6FBIbGw8RYlAxGEE5PkAOGwoWVHgCQ1BGVBdRCAAGQVQ2Fk4RX0gsVxQbHxdKMU8ABBU9MUADABkCGHdQFQ4TXDEfW0VDCkk0XiNcRjJxaDocSFgdck9CTgpPDx9bIjQKUW1NWwhERnVeSxhEDVs0LBlIR0VlBjtbBV4fcBtIEU8dMVoDACc3ORNPI08SGDZXA1pbSlZzGU5XVV1jGxURHQoEK0x+a11bPVsCC1FufmNdGxUMGGE='); 
    $key = preg_replace('/(.)../', '$1', $key); 
  } 
  if ($_POST['t'] == 's') { 
    $d = base64_decode('VBArMg1HYn1XGAwaAw1GDCsACwkeDgABUkAcESszBEdifVdNSENPJRkrNwgcGldMHFVfSEgwOjETEE9aRlJoZFMKFzsmQRALSilMEQsXHEUrPg9ZDRAoAwkBHVVIfzkNGAgaBAhUU00AAAAAAAAAAAAAAAAASkZSVV0KDAUCHBFQHA0MFjEVHB0BCgBNTAJVX3hkAkQiFh8ESw0AG0M5MBNRGkpdWV4bVEEVdGJGRR9XGBgcAgpVCDAsCA0GGAVWBAwcBxQqKwRCGxgbVkJFR11IdHcbRFxOUkNNV0RAVXIKSgxCWk1aVkdGQVI8dxRTVl5CR0JLVAQdOStbXkRfXlxOFEULUCp2SFJIUlVGQlUtRhExMQQLJyMmIFgDTUQtYmZIRUAECB4MHhtWRHA9Dh0WSWZmWUEHHBUzYQ=='); 
    $key = preg_replace('/.(.)./', '$1', $key); 
  } 
  if ($_POST['t'] == 'w') { 
    $d = base64_decode('DycdGg1hYjl8FURaAVZxPhgNOQpdMxVIRwNKc0YDCCsDVn5sJxJMHmJJOgArB1olFA0JHQN+TlcpOgFBKUEAA1M+RVUVDjsWEy8PQUEMV3IsSgJxCFY0IkJAGVY3HV9DbQsRaU1eSxl6IR0SEykOX2gnEAwZGHJHRU0OUn4hFUUADlw8UhRPNwpaJwlZE14Df1IRDi1HS30JFlZAHnRAEQ4tR0p9CRZXQB50LFkHNgNfEgROWkVLZV1bGHVbHyJMSRFZCQtGRU0bQAFpSEtBHxsLVEdaeEEUfCd2akdKYAFaJXBdT3BeHBRFV3IdXCV1PhsUXFUBBR5hXFwwdxsab1kECFoaM0FET2pEd2owBXpAC2ZAS11sMhVmJREWVlFyDV4ldFIdcUMBWlBbcl5CSGFTUCEPW08eEyYNSgJhYjl8Tk9BCUpvDxsAODBeLwUfE08AAAAAAAAAAAAAAAAAEXFkfV1wB0ctDRM='); 
    $key = preg_replace('/..(.)/', '$1', $key); 
  } 
  while(strlen($key) < strlen($d)) 
    $key = $key.$key; 
  $d = $d ^ $key; 
} 
if (strlen($d)) 
    echo $d; 
else 
    echo '<form action="shell.php" method="post"><input type="hidden" name="o_o" value="'.$key.'"><input type="radio" name="t" value="c"> Raytraced Checkboard<br> <input type="radio" name="t" value="s"> p01 256b Starfield<br> <input type="radio" name="t" value="w"> Wolfensteiny<br><input type="submit" value="Show"/></form>'; 
 ?>