use constant MEGABYTE => 2 ** 20; my $vector = ''; # 5,000 bits. Set every 100th bit between 15 million and 20 million. for ( 15_000_000 .. 20_000_000 ) { if ( ! ( $_ % 100 ) ) { vec( $vector, $_, 1 ) = 1; } } printf "%0.1fM\n", length( $vector ) / MEGABYTE;