#code from the Perl Cookbook: see the link above for credits

sub weight_to_dist {
    my %weights = @_;
    my %dist    = ();
    my $total   = 0;
    my ($key, $weight);
    local $_;

    foreach (values %weights) {
        $total += $_;
    }
    
    while ( ($key, $weight) = each %weights ) {
        $dist{$key} = $weight/$total; 
    }
    
    return %dist;
}

sub weighted_rand {
    my %dist = @_;
    my ($key, $weight);

    while (1) {  # to avoid floating point inaccuracies
      my $rand = rand;
      while ( ($key, $weight) = each %dist ) {
          return $key if ($rand -= $weight) < 0;
      }
    }
}