php模拟js函数unescape的函数代码操作，解析escape后的数据

[PHP]代码

function unescape($str)  {  $ret = '';  $len = strlen($str);    for ($i = 0; $i < $len; $i++)  {  if ($str[$i] == '%' && $str[$i+1] == 'u')  {  $val = hexdec(substr($str, $i+2, 4));    if ($val < 0x7f) $ret .= chr($val);  else if($val < 0x800) $ret .= chr(0xc0|($val>>6)).chr(0x80|($val&0x3f));  else $ret .= chr(0xe0|($val>>12)).chr(0x80|(($val>>6)&0x3f)).chr(0x80|($val&0x3f));    $i += 5;  }  else if ($str[$i] == '%')  {  $ret .= urldecode(substr($str, $i, 3));  $i += 2;  }  else $ret .= $str[$i];  }  return $ret;  }