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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 
}

sub is_power_of_2 {
  local $_ = $_[0];
...
  return if ($_ - int($_));
  1;
}