From: Jeff King <peff@peff.net>
Date: Wed, 13 Jul 2011 06:37:01 GMT
Subject: Re: [PATCH 2/5] add object-cache infrastructure
Message-ID: <20110713063701.GA18238@sigill.intra.peff.net>
In-Reply-To: <7v62n78hpk.fsf@alter.siamese.dyndns.org>

On Tue, Jul 12, 2011 at 11:41:27AM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> >   2. The disk store uses a binary search over a sorted list of sha1s.
> >      Generalizing this to "a sequence of bytes" would not be hard. But
> >      we currently have the option of using the uniform distribution of
> >      sha1 to make better guesses about our "middle" (see the comments in
> >      sha1-lookup.c). That assumption does not hold over arbitrary bytes.
> 
> A side note. I notice that the "comment" you refer to appears twice in the
> file, and the sha1_pos() function that comes earlier in the file does not
> protect itself from overshoot penalty like the sha1_entry_pos() function
> does.
> 
> Perhaps we should think about unifying them somehow.

It would be easy to implement sha1_entry_pos in terms of sha1_pos by
writing an access function. But it seems unnecessarily slow to add
function call overhead in what should be a fairly tight loop.

OTOH, we do it everywhere else that we call sha1_pos; either it isn't a
big deal, or nobody has bothered to measure and micro-optimize there
yet.

-Peff