Re: [PATCH 2/3] exclude: do strcmp as much as possible before fnmatch

From: Nguyen Thai Ngoc Duy <pclouds@gmail.com>
Date: May 27, 2012, 12:06 UTC
Message-ID: <CACsJy8DOz30GD_zv9yO7KD55+=H0t=+q_5qRtt51nOoYXwOBBQ@mail.gmail.com>
In-Reply-To: <7vk3zyp14i.fsf@alter.siamese.dyndns.org>

On Sun, May 27, 2012 at 1:51 PM, Junio C Hamano <gitster@pobox.com> wrote:

Show 15 quoted lines

> Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
>
>> this also avoids calling fnmatch() if the non-wildcard prefix is
>> longer than basename
>>
>> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
>> ---
>
> I have been wondering if you can take a different approach based on the
> same observation this patch is based on.  If you see an entry /foo/bar/*.c
> in the top-level .gitignore, perhaps you can set it aside in a different
> part of "struct exclude" for the top-level directory (because the pattern
> will never match outside foo/bar directory), so that it is not even used
> for matching, and only when you descend to foo/bar directory, add "/*.c"
> to the "struct exclude" you create for that directory.

that part is "base" field in "struct exclude", I believe.

> That way, instead of "strcmp is faster than fnmatch, but we always compare
> all elements in the huge pattern list given at the toplevel", you would be
> doing "we do not even bother to compare with the elements we know do not
> matter", which would be far more efficient, no?

You still have to do at least one strncmp on "base" though to know if a pattern is applicable to the given directory. So it's not really cheaper than what is done in 3/3.

-- 
Duy