why GNU grep is fast

[Gabor Kovesdan]

>
>> Later on, he summarizes some of the existing implementations, 
>> including comments about the Plan 9 implementation and his own RE2, 
>> both of which efficiently handle international text (which seems to 
>> be a major concern of Gabor's).
>
> I believe Gabor is considering TRE for a good replacement regex library.
Yes. Oniguruma is slow, Google RE2 only supports Perl and fgrep syntax 
but not standard regex and Plan 9 implementation iirc only supports 
fgrep syntax and Unicode but not wchar_t in general.
>
>> The key comment in Mike's GNU grep notes is the one about not 
>> breaking into lines.  That's simply double-scanning the input; 
>> instead, run the matcher over blocks of text and, when it finds a 
>> match, work backwards from the match to find the appropriate line 
>> beginning.  This is efficient because most lines don't match.
>
> I do like the idea.
So do I.
>
> BTW, the fastgrep portion of bsdgrep is my fault/contribution to do a 
> faster search bypassing the regex library.  :)  It certainly was not 
> written with any encodings in mind; it was purely ASCII.  As I have 
> not kept up with it, I do not know if anyone improved it or not.
>
It has been made wchar-compliant.

Gabor