Re: Why SHA are 40 bytes? (aka looking for flames)

From: Shawn O. Pearce <spearce@spearce.org>
Date: Apr 24, 2007, 02:30 UTC
Message-ID: <20070424023035.GK17480@spearce.org>
In-Reply-To: <462D5370.8040905@zytor.com>

"H. Peter Anvin" <hpa@zytor.com> wrote:

Show 8 quoted lines

> Nicolas Pitre wrote:
> >
> >Object names aren't 40 bytes.  They are 20 bytes.
> >It  is their hex representation that takes 40 bytes.
> >
> 
> Sure, but that's the way they're stored in *most* git objects, in 
> particular in commit objects.

But OBJ_TREE occurs more often, and its 20 bytes binary for a SHA-1 in those. They are only ASCII hex in OBJ_COMMIT and OBJ_TAG.

If Nico and I ever get pack v4 done, all SHA-1s drop to 24 bytes worst case, or 20 + (4 * n_references) best case. Typically we found that n_references was large enough, frequently enough, that we shaved 5% or so off linux-2.6.git. And I don't think that's including the 20 * n_objects saved out of the .idx files...

-- 
Shawn.