In my problem '01' is different than '10', and I need to count them separately. Still, your point of not needing to count the last is well taken, as I can count 3, and thereby know the 4th. However, by doing this, I'm not seeing any significant performance gains, and it may be a bit slower.

              Rate browser+LR  browserUK
browser+LR 19055/s         --        -2%
browserUK  19509/s         2%         --
[download]

Code for benchmarking...