Study doesn't do anything really interesting, but neither is creating a keyword index for a keyword based search all that interesting either. Considering that

Study doesn't do anything really interesting, but neither is creating a keyword index for a keyword based search all that interesting either. Considering that Google code search is not intended to search English (for which their regular search technology would most likely suffice for that) using regular expressions, then I agree that the naive study implementation you've quoted is, basically, not what Google is using for code search. However, there's no reason that the frequency tables need to be static nor need to be constructed solely from from C programs and English text. Frequency tables can be continuously updated based on the input corpus and the input corpus should be the code that is being searched. Part of search is being able to rule out significant portions of the search space in the name of getting positive results as fast as possible, so being able to fail quickly for most inputs (considering the example regular expression only returns three hits, it seems a wide majority don't match), a study-like implementation would appear to be a possibility.