sub hanoi {
    my ($n, $a, $b, $c) = @_;
    
    return if $n < 1;

    hanoi($n-1, $a, $c, $b);
    print "Moving plate from $a to $b\n";
    return hanoi($n-1, $c, $b, $a);
}

-- Example of call
$ hanoi(8, "A", "B", "C")
=> 2^8 - 1 moves
    
-- Comment
   $n is the number of plates (> 0) to move
   from pole A to pole B using auxiliary pole C 
   
   The final 'return' allows for a slight
   tail-call optimization


##</code><code>##

##
# hanoi n a b c
# Without recursivity nor goto.
# Franck PORCHER

use constant log_2 => log(2);

sub hanoi {
   my ($n, $a, $b, $c) = @_;

   my $p = 1;
   my $k;

   do {
      if ( $n ) {
         $p <<= $n;
         ($b, $c) = ($c, $b) if ($n & 1);
         $n = 0;
      }

      if ( ($p - 1) && ( $p & 1) ){
         $k   = log(($p ^ ($p + 1)) & ($p + 1)) / log_2;
         $p >>= $k;
         ($a, $b) = ($b, $a) if ($k & 1);
         $n += $k;
         $p ||= 1;
      }
 
      if ( $p - 1 ) {
         print "Moving plate from $a to $b\n";
         ($a, $b, $c) = ($c, $a, $b);
         $p++;
      }

   } while $p - 1;
}

-- Example of call
$ hanoi(8, "A", "B", "C")
=> 2^8 - 1 moves