If your pattern is relatively complex (ie complex enough that you'd want to use the regexp engine rather than index()) it might be worth constructing the 8 shifted variants of the pattern so that you can combine them into a single regexp to run over the target string.

For simple patterns or short strings, unpacking the bytes is probably faster.

I'm not familiar with Bit::Vector, so I don't know where that would fit into the efficiency mix.

(This is a gut feel, I welcome benchmarks agreeing or disagreeing with that. :)

Hugo