c:\@Work\Perl>perl -wMstrict -le
"(source code as above)
"
Perl version: 5.008009
length: 140000000
              Rate  [Aa]{2}       /i [Aa][Aa]
[Aa]{2}  3276565/s       --      -6%     -16%
/i       3480139/s       6%       --     -11%
[Aa][Aa] 3918166/s      20%      13%       --