php生成固定长度纯数字编码的方法

<php
/**
 * 根据日期或者是给定前缀生成唯一编号
 * User: minyifei.cn
 * Date: 15/7/7
 */
namespace Minyifei\Libs;
class SequenceNumber {
 /**
  * 根据显示宽度获取指定的 mapbit
  *
  * @param integer $width 编号显示宽度
  *
  * @return array
  */
 private static function _getMapbit($width)
 {
  $mapBits = array(
   4=>array(
    10, 2, 11, 3, 0, 1, 9, 7, 12, 6, 4, 8, 5,
   ),
   5=>array(
    4, 3, 13, 15, 7, 8, 6, 2, 1, 10, 5, 12, 0, 11, 14, 9,
   ),
   6=>array(
    2, 7, 10, 9, 16, 3, 6, 8, 0, 4, 1, 12, 11, 13, 18, 5, 15, 17, 14,
   ),
   7=>array(
    18, 0, 2, 22, 8, 3, 1, 14, 17, 12, 4, 19, 11, 9, 13, 5, 6, 15, 10, 16, 20, 7, 21,
   ),
   8=>array(
    11, 8, 4, 0, 16, 14, 22, 7, 3, 5, 13, 18, 24, 25, 23, 10, 1, 12, 6, 21, 17, 2, 15, 9, 19, 20,
   ),
   9=>array(
    24, 23, 27, 3, 9, 16, 25, 13, 28, 12, 0, 4, 10, 18, 11, 2, 17, 1, 21, 26, 5, 15, 7, 20, 22, 14, 19, 6, 8,
   ),
   10=>array(
    32, 3, 1, 28, 21, 18, 30, 7, 12, 22, 20, 13, 16, 15, 6, 17, 9, 25, 11, 8, 4, 27, 14, 31, 5, 23, 24, 29, 0, 10, 19, 26, 2,
   ),
   11=>array(
    9, 13, 2, 29, 11, 32, 14, 33, 24, 8, 27, 4, 22, 20, 5, 0, 21, 25, 17, 28, 34, 6, 23, 26, 30, 3, 7, 19, 16, 15, 12, 31, 1, 35, 10, 18,
   ),
   12=>array(
    31, 4, 16, 33, 35, 29, 17, 37, 12, 28, 32, 22, 7, 10, 14, 26, 0, 9, 8, 3, 20, 2, 13, 5, 36, 27, 23, 15, 19, 34, 38, 11, 24, 25, 30, 21, 18, 6, 1,
   ),
  );
  return $mapBits[intval($width)];
 }
 /**
  * 格式化给定时间戳
  *
  * @param integer $ts timestamp, if null use current timestamp
  *
  * @return string
  */
 private static function _fmtTS($ts=null)
 {
  $ts = $ts : time();
  return date(self::$_fmt, $ts);
 }
 /**
  * 根据id获取一个随机唯一编码
  * @param $id 编号
  * @param int $prefix 前缀
  * @param int $width 除前缀外长度
  * @return string
  */
 public static function generateNumber($id,$prefix=10,$width=8)
 {
  return sprintf("%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));
 }
}