Re: [PATCH] block-sha1: more good unaligned memory access candidates

From: Nicolas Pitre <nico@cam.org>
Date: Aug 13, 2009, 20:13 UTC
Message-ID: <alpine.LFD.2.00.0908131603240.10633@xanadu.home>
In-Reply-To: <7v63crbja2.fsf@alter.siamese.dyndns.org>

On Thu, 13 Aug 2009, Junio C Hamano wrote:

Show 16 quoted lines

> Nicolas Pitre <nico@cam.org> writes:
> 
> > As it is now, I was about to suggest:
> >
> > 	git mv block-sha1/sha1.[ch] .
> > 	rmdir block-sha1
> > 	rm -r mozilla-sha1
> > 	rm -r arm
> > 	rm -r ppc 
> >
> > and remove support for openssl's SHA1 usage, making this implementation 
> > unconditional.  After all it is faster, or so close to be faster than 
> > the alternatives, that we should probably cut on the extra dependency 
> > and simplify portability issues at the same time.
> 
> Wow.  Is it now faster than the arm/ and ppc/ hand-tweaked assembly?

It is indeed faster than the ARM assembly version by far, and faster than all the alternative implementations too, but with a 7x increase in compiled code size. In the context of Git I think this is a good compromize. Making the assembly version faster than the C version could be possible, but that would require quite some work and I don't expect the gain to be significant, certainly not worth the trouble.

Furthermore the C version can be used to generate ARM Thumb code while the asm version cannot without yet more work.

Nicolas