Check if variable is serialized in PHP

Want to check if a variable is serialized or not in PHP? Here you go ....

/**
 * This program is free software. It comes without any warranty, to
 * the extent permitted by applicable law. You can redistribute it
 * and/or modify it under the terms of the Do What The Fuck You Want
 * To Public License, Version 2, as published by Sam Hocevar. See
 * http://sam.zoy.org/wtfpl/COPYING for more details.
 */ 

/**
 * Tests if an input is valid PHP serialized string.
 *
 * Checks if a string is serialized using quick string manipulation
 * to throw out obviously incorrect strings. Unserialize is then run
 * on the string to perform the final verification.
 *
 * Valid serialized forms are the following:
 * 
 * 
boolean: b:1;
 * 
integer: i:1;
 * 
double: d:0.2;
 * 
string: s:4:"test";
 * 
array: a:3:{i:0;i:1;i:1;i:2;i:2;i:3;}
 * 
object: O:8:"stdClass":0:{}
 * 
null: N;
 * 
 *
 * @author  Chris Smith 
 * @copyright Copyright (c) 2009 Chris Smith (http://www.cs278.org/)
 * @license  http://sam.zoy.org/wtfpl/ WTFPL
 * @param  string $value Value to test for serialized form
 * @param  mixed $result Result of unserialize() of the $value
 * @return  boolean   True if $value is serialized data, otherwise false
 */
function is_serialized($value, &$result = null)
{
 // Bit of a give away this one
 if (!is_string($value))
 {
  return false;
 }

 // Serialized false, return true. unserialize() returns false on an
 // invalid string or it could return false if the string is serialized
 // false, eliminate that possibility.
 if ($value === 'b:0;')
 {
  $result = false;
  return true;
 }

 $length = strlen($value);
 $end = '';

 switch ($value[0])
 {
  case 's':
   if ($value[$length - 2] !== '"')
   {
    return false;
   }
  case 'b':
  case 'i':
  case 'd':
   // This looks odd but it is quicker than isset()ing
   $end .= ';';
  case 'a':
  case 'O':
   $end .= '}';

   if ($value[1] !== ':')
   {
    return false;
   }

   switch ($value[2])
   {
    case 0:
    case 1:
    case 2:
    case 3:
    case 4:
    case 5:
    case 6:
    case 7:
    case 8:
    case 9:
    break;

    default:
     return false;
   }
  case 'N':
   $end .= ';';

   if ($value[$length - 1] !== $end[0])
   {
    return false;
   }
  break;

  default:
   return false;
 }

 if (($result = @unserialize($value)) === false)
 {
  $result = null;
  return false;
 }
 return true;
}