之前面试的时候，有面试官和我说md5做不了短链接，我也不知道他是怎么做，我感觉这样的做法应该没问题啊！

<?php
   $or_url    = $_GET['or_url'];
   $md5_url   = md5($or_url);
   
   $salt      = '0826';//这里不高于aaaa就不会出现61以上的数字，所以来说，后面的特别符号是不会出现的！
   $md5_url   = addSalt($md5_url,$salt);
   
   $short_url = '';
   
   for($i=0;$i<6;$i++){
   $current_str = substr($md5_url,$i*6,6);
   //处理当前串的值
   $short_url .= ZChar($current_str);
   }
   
   echo $short_url;
   
   function addSalt($md5_url,$salt){
   if(strlen($md5_url) != 32){
   die('addSalt:{$md5_url} error');
   }
   $len  = strlen($salt);
   for($i=0;$i<$len;$i++){
   $position = hexdec($md5_url[$i]);
   $weight   = ceil($position/8);
   $position = $position * $weight;
   $pre      = substr($md5_url,0,$position);
   $next     = substr($md5_url,$position);
   $md5_url  = $pre.$salt[$i].$next;
   }
   return $md5_url;
   }
   
   function dealStr($str){
   if(strlen($str) != 6){
   die("dealStr:{$str}error");
   }
   $count = '';
   for($i=0;$i<6;$i++){
   //加权,避免不同序列的和一致
   $number = hexdec($str[$i])*($i+1)%12;
   $count += $number;
   }
   
   return $count % 66;
   }
   
   function ZChar($current_str){
   $Vchar = dealStr($current_str);
   return char($Vchar);
   }
   
   
   function char($char_point){
   
    $char_array = ["0","1","2","3","4","5",   
                "6","7","8","9","a","b","c","d",
"e","f","g","h","i","j","k","l",
"m","n","o","p","q","r","s","t",
"u","v","w","x","y","z","A","B",
"C","D","E","F","G","H","I","J",
"K","L","M","N","O","P","Q","R",
"S","T","U","V","W","X","Y","Z",
"$","@",'+',"="];
    $char_point = intval($char_point);
if($char_point < 0 || $char_point > 65){
die('char:'.$char_point.' error');
}
    
return $char_array[$char_point];
   }
?>