my(@F, @G);
@F = (
      1,
      2,
      4,
      8,
      16,
      32..64
     );

#Generate a reverse map
for(my $i=0; $i<scalar @F; $i++){
  $G[$F[$i]] = $i;
}

sub range{
  my($lo, $hi) = @_;
  $lo++ until defined($G[$lo]);
  $hi-- until defined($G[$hi]);
  return $lo .. $hi;
}

print join(',', range(25,35)), "\n";
print join(',', range(50,75)), "\n";