Lynn Allan wrote:
Eric N. wrote during 2005
do to make Boyer-Moore work with the regex traits interface make Boyer-Moore more trouble than its worth for case-insensitive matches. I haven't yet run the other tests.
Just curious ... does xpressive use "standard" Boyer-Moore or a variant? In my limited experience, the Horspool variant of Boyer-Moore is simpler and tends to be faster. It may be more or less prone to have problems with "pathological" cases than "standard" Boyer-Moore, however.
Xpressive uses a home-grown variant of Horspool. It's an extension to the algorithm that allows it to perform case-insensitive matches. It also works with large character sets, such as Unicode, which standard Horspool does not, IIUC. It yields potential matches, not exact matches. Only if it finds a tentative match is a full regex match attepted. Since I wrote the above, I have fixed the performance problem with BMH and case-insensitive matches by extended the regex traits class with a function that returns all the case-folded equivalents of a character. This resulted in a significant performance improvement for case-insensitive matches. HTH, -- Eric Niebler Boost Consulting www.boost-consulting.com