alphaID - Translates a number to a short alhanumeric version

Translates a number to a short alhanumeric version. e.g.: 9007199254740989 --> PpQXn7COf

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.

more info on limitation: http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/165372

 "alphaID maker"

/**
 * 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.
 *
 * The following code block can be utilized by PEAR's Testing_DocTest
 * 
 * // Input //
 * $number_in = 2188847690240;
 * $alpha_in  = "SpQXn7Cb";
 *
 * // Execute //
 * $alpha_out  = alphaID($number_in, false, 8);
 * $number_out = alphaID($alpha_in, true, 8);
 *
 * if ($number_in != $number_out) {
 *	 echo "Conversion failure, ".$alpha_in." returns ".$number_out." instead of the ";
 *	 echo "desired: ".$number_in."
";
 * }
 * if ($alpha_in != $alpha_out) {
 *	 echo "Conversion failure, ".$number_in." returns ".$alpha_out." instead of the ";
 *	 echo "desired: ".$alpha_in."
";
 * }
 *
 * // Show //
 * echo $number_out." => ".$alpha_out."
";
 * echo $alpha_in." => ".$number_out."
";
 * echo alphaID(238328, false)." => ".alphaID(alphaID(238328, false), true)."
";
 *
 * // expects:
 * // 2188847690240 => SpQXn7Cb
 * // SpQXn7Cb => 2188847690240
 * // aaab => 238328
 *
 * 
 *
 * @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  <
      $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;
}
 
echo alphaID(123564852136); //out = eG6vSkc