Re: [PATCH] match_pathname(): give fnmatch one char of prefix context

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 26, 2025, 23:29 UTC
Message-ID: <xmqq7bwhmecb.fsf@gitster.g>
In-Reply-To: <20251026152614.GB2095501@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

> I also wonder how expensive that memcmp() is. ;) Obviously not very, but
> if the point is that we are trying to save fnmatch from looking at that
> one extra character, we already pinching pennies in a mostly
> un-measurable way.

I added the "limit to known bad case" in the illustration not for performance but for correctness. This was because just like we weren't convinced that the "**/" may be the only case that breaks the existing optimization, I was worried if stepping back by one byte may somehow make a pattern that should not match mistakenly match.

In any case, your numbers did make sense and tells us that optimized strncmp() is much faster than comparing a byte at a time, which is expected.

Thanks.