Re: [PATCH 0/4] hash.h: support choosing a separate SHA-1 for non-cryptographic uses

> Taylor Blau <me@ttaylorr.com> writes:
>
> > After some profiling, I noticed that we spend a significant amount of
> > time in hashwrite(), which is not all that surprising. But much of that
> > time is wasted in GitHub's infrastructure, since we are using the same
> > collision-detecting SHA-1 implementation to produce a trailing checksum
> > for the pack which does not need to be cryptographically secure.
>
> Cute.
>
> I wish we can upgrade the file formats so that a writer can choose
> the hash algorithm independently from whatever the payload uses.
> Most of our use of the tail sum are for files that are consumed
> locally in the same repository so nobody shouldn't need to know that
> you are using xxHash for the tail sum instead.

> Except that the story is not so simple for packfiles, which is named
> after the file's tail sum, so you cannot use a hash algorithm of
> your choice independently without affecting other folks.  All other
> csum-file protected file types are lot smaller than the pack files
> to matter, sadly.