<"%s%s", $prefix,self::encode($id, $width));
 }
 /**
  * 编码转换
  *
  * @param integer $id id
  * @param integer $width 编号额外组成部分的显示宽度
  *
  * @return integer
  */
 public static function encode($id, $width)
 {
  $maximum = intval(str_repeat(9, $width));
  $superscript = intval(log($maximum) / log(2));
  $r = 0;
  $sign = 0x1 << $superscript;
  $id |= $sign;
  $mapbit = self::_getMapbit($width);
  for ($x = 0; $x < $superscript; $x++) {
   $v = ($id  $x) & 0x1;
   $r |= ($v << $mapbit[$x]);
  }
  $r += $maximum - pow(2, $superscript) + 1;
  return sprintf("%0${width}s", $r);
 }
 /**
  * 获取唯一编号
  *
  * @param integer $id id, mostly database primary key
  * @param integer $width 编号显示宽度
  * @param integer $ts timestamp
  *
  * @return string
  */
 public static function get($id, $width, $ts=null)
 {
  return sprintf('%s%s', self::_fmtTS($ts), self::encode($id, $width));
 }
}