<?php 

/**  

 * @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  < 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;

}