alphaID(12354）；  //会将数字转换为字母。    alphaID('PpQXn7COf',true）；//会将字母ID转换为对应的数字。    alphaID(12354,false,6）；//指定生成字母ID的长度为6.

<?php /**  * Translates a number to a short alhanumeric version  *  * Translated any number up to 9007199254740992  * to a shorter version in letters e.g.:  * 9007199254740989 --> PpQXn7COf  *  * specifiying the second argument true, it will  * translate back e.g.:  * PpQXn7COf --> 9007199254740989  *  * this function is based on any2dec && dec2any by  * fragmer[at]mail[dot]ru  * see: http://nl3.php.net/manual/en/function.base-convert.php#52450  *  * If you want the alphaID to be at least 3 letter long, use the  * $pad_up = 3 argument  *  * In most cases this is better than totally random ID generators  * because this can easily avoid duplicate ID's.  * For example if you correlate the alpha ID to an auto incrementing ID  * in your database, you're done.  *  * The reverse is done because it makes it slightly more cryptic,  * but it also makes it easier to spread lots of IDs in different  * directories on your filesystem. Example:  * $part1 = substr($alpha_id,0,1);  * $part2 = substr($alpha_id,1,1);  * $part3 = substr($alpha_id,2,strlen($alpha_id));  * $destindir = "/".$part1."/".$part2."/".$part3;  * // by reversing, directories are more evenly spread out. The  * // first 26 directories already occupy 26 main levels  *  * more info on limitation:  * - http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/165372  *  * if you really need this for bigger numbers you probably have to look  * at things like: http://theserverpages.com/php/manual/en/ref.bc.php  * or: http://theserverpages.com/php/manual/en/ref.gmp.php  * but I haven't really dugg into this. If you have more info on those  * matters feel free to leave a comment.  *  * @author  Kevin van Zonneveld <kevin@vanzonneveld.net>  * @author  Simon Franz  * @author  Deadfish  * @copyright 2008 Kevin van Zonneveld (http://kevin.vanzonneveld.net)  * @license   http://www.opensource.org/licenses/bsd-license.php New BSD Licence  * @version   SVN: Release: $Id: alphaID.inc.php 344 2009-06-10 17:43:59Z kevin $  * @link    http://kevin.vanzonneveld.net/  *  * @param mixed   $in    String or long input to translate  * @param boolean $to_num  Reverses translation when true  * @param mixed   $pad_up  Number or boolean padds the result up to a specified length  * @param string  $passKey Supplying a password makes it harder to calculate the original ID  *  * @return mixed string or long  */ function alphaID($in, $to_num = false, $pad_up = false, $passKey = null) {   $index = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";   if ($passKey !== null) {     // Although this function's purpose is to just make the     // ID short - and not so much secure,     // with this patch by Simon Franz (http://blog.snaky.org/)     // you can optionally supply a password to make it harder     // to calculate the corresponding numeric ID     for ($n = 0; $n<strlen($index); $n++) {       $i[] = substr( $index,$n ,1);     }     $passhash = hash('sha256',$passKey);     $passhash = (strlen($passhash) < strlen($index))       ? hash('sha512',$passKey)       : $passhash;     for ($n=0; $n < strlen($index); $n++) {       $p[] =  substr($passhash, $n ,1);     }     array_multisort($p,  SORT_DESC, $i);     $index = implode($i);   }   $base  = strlen($index);   if ($to_num) {     // Digital number  <<--  alphabet letter code     $in  = strrev($in);     $out = 0;     $len = strlen($in) - 1;     for ($t = 0; $t <= $len; $t++) {       $bcpow = bcpow($base, $len - $t);       $out   = $out + strpos($index, substr($in, $t, 1)) * $bcpow;     }     if (is_numeric($pad_up)) {       $pad_up--;       if ($pad_up > 0) {         $out -= pow($base, $pad_up);       }     }     $out = sprintf('%F', $out);     $out = substr($out, 0, strpos($out, '.'));   } else {     // Digital number  -->>  alphabet letter code     if (is_numeric($pad_up)) {       $pad_up--;       if ($pad_up > 0) {         $in += pow($base, $pad_up);       }     }     $out = "";     for ($t = floor(log($in, $base)); $t >= 0; $t--) {       $bcp = bcpow($base, $t);       $a   = floor($in / $bcp) % $base;       $out = $out . substr($index, $a, 1);       $in  = $in - ($a * $bcp);     }     $out = strrev($out); // reverse   }   return $out; }