Re: A look at some alternative PACK file encodings

From: Nicolas Pitre <nico@cam.org>
Date: Sep 7, 2006, 17:32 UTC
Message-ID: <Pine.LNX.4.64.0609071322010.18635@xanadu.home>
In-Reply-To: <20060907090756.30111.qmail@science.horizon.com>

On Thu, 7 Sep 2006, linux@horizon.com wrote:

Show 9 quoted lines

> > Support for 'thin' packs would pretty much require mixing IDs and
> > (relative) offsets in the same pack file.
> 
> An alternative would be to create a small "placeholder" object that
> just gives an ID, then refer to it by offset.
> 
> That would avoid the need for an id/offset bit with every offset,
> and possibly save more space if the same object was referenced
> multiple times.

Well... I'm using object type 6 for deltas with offset reference (instead of object type 7 that is delta with sha1 reference). So there is no extra bit needed and no backward compatibility breakage.

There could be of course a new object type which payload is only a sha1 that deltas type 6 reference. But that can be introduced at a later date if it turns out to be worthwhile (i.e. the actual saving in real use scenarios is worth the (small but still) added complexity).

> And it just seems simpler.

Well I would not say so. Simply prefixing a delta with the sha1 of its base object cannot be simpler when streaming out a pack.

Nicolas