I doubt that even a pure C solution using this technique would be much faster. I haven't profiled it, but I'd guess most of the time is in the index and that is likely pretty efficient anyway.

I think some fussy code could handle the special case without impacting performance too much. The key would be detecting that a search sub-pattern was a repeating pattern and then "drifting" the pattern left by the repeat length to see if there is an earlier match against the target string than was found by index. Maybe I need to write some code so you see what I mean? :)