sub is_power_of_2 {
  return 0 unless $_[0]>0; # to avoid log error
  log($_[0])/log(2) - int(log($_[0])/log(2)) ? 0 : 1 
}

##</code><code>##

sub is_power_of_2 {
  local $_ = $_[0];
  $_/=2 while ($_ > 1);
  return if ($_ - int($_));
  1;
}