sub buk2 {
	use List::Util qw[sum];
	return undef unless exists $_[0]->{ $_[1] }
	                and exists $_[0]->{ $_[2] };

	return sum( @{ $_[0] }{ $_[1] .. $_[2] } ) / ( $_[2] - $_[1] + 1 );
}

__END__
P:\test>278169
0.503353665487943
0.503353665487943
0.503353665487943
       Rate orig  buk buk2
orig 1.30/s   -- -41% -81%
buk  2.19/s  69%   -- -67%
buk2 6.70/s 417% 206%   --