php短网址和数字之间相互转换的方法

<?php
/**
 * 将数字转为短网址代码
 *
 * @param int $number 数字
 * @return string 短网址代码
 */
function generate_code($number) {
  $out  = "";
  $codes = "abcdefghjkmnpqrstuvwxyz23456789abcdefghjkmnpqrstuvwxyz";
  while ($number > 53) {
    $key  = $number % 54;
    $number = floor($number / 54) - 1;
    $out  = $codes{$key}.$out;
  }
  return $codes{$number}.$out;
}
/**
 * 将短网址代码转为数字
 *
 * @param string $code 短网址代码
 * @return int 数字
 */
function get_num($code){
  $codes = "abcdefghjkmnpqrstuvwxyz23456789abcdefghjkmnpqrstuvwxyz";
  $num = 0;
  $i = strlen($code);
 for($j=0;$j<strlen($code);$j++){
    $i--;
    $char = $code{$j};
    $pos = strpos($codes,$char);
    $num += (pow(54, $i) * ($pos + 1));
  }
  $num--;
  return $num;
}