From: Paolo Bonzini <bonzini@gnu.org>
To: Nicolas Pitre <nico@cam.org>
Cc: George Spelvin <linux@horizon.com>,
bdonlan@gmail.com, johnflux@gmail.com, P@draigBrady.com,
art.08.09@gmail.com, git@vger.kernel.org
Subject: Re: Linus' sha1 is much faster!
Date: Mon, 17 Aug 2009 19:20:18 +0200 [thread overview]
Message-ID: <4A899152.8070607@gnu.org> (raw)
In-Reply-To: <alpine.LFD.2.00.0908171228570.6044@xanadu.home>
> my first version of
> get_be32() was a macro that did this:
>
> #define SHA_SRC(t) \
> ({ unsigned char *__d = (unsigned char *)&data[t]; \
> (__d[0]<< 24) | (__d[1]<< 16) | (__d[2]<< 8) | (__d[3]<< 0); })
>
> With such a construct, gcc would always allocate a register to hold __d
> and then dereference that with an offset from 0 to 3. Whereas:
>
> #define SHA_SRC(t) \
> ({ unsigned char *__d = (unsigned char *)data; \
> (__d[(t)*4 + 0]<< 24) | (__d[(t)*4 + 1]<< 16) | \
> (__d[(t)*4 + 2]<< 8) | (__d[(t)*4 + 3]<< 0); })
>
> does produce optimal assembly as only the register holding the data
> pointer is dereferenced with the absolute byte offset. I suspect your
> usage of inline functions has the same effect as the first SHA_SRC
> definition above.
Yes, that's what happens.
Paolo
next prev parent reply other threads:[~2009-08-17 17:20 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-17 7:23 Linus' sha1 is much faster! George Spelvin
2009-08-17 14:20 ` Nicolas Pitre
2009-08-17 17:06 ` Nicolas Pitre
2009-08-17 17:20 ` Paolo Bonzini [this message]
2009-08-17 18:54 ` George Spelvin
2009-08-17 19:34 ` Nicolas Pitre
2009-08-17 23:12 ` George Spelvin
-- strict thread matches above, loose matches on Subject: below --
2009-08-14 23:25 Pádraig Brady
2009-08-15 20:02 ` Bryan Donlan
2009-08-15 20:12 ` John Tapsell
2009-08-15 20:23 ` Linus Torvalds
2009-08-15 20:54 ` Linus Torvalds
2009-08-17 1:55 ` Nicolas Pitre
2009-08-26 11:39 ` Pádraig Brady
2017-04-20 21:35 ` galt
2017-04-20 21:38 ` galt
2009-08-17 8:22 ` Andreas Ericsson
2009-08-16 0:06 ` Theodore Tso
2009-08-16 19:25 ` Giuseppe Scrivano
2009-08-16 20:10 ` Linus Torvalds
2009-08-16 22:15 ` Giuseppe Scrivano
2009-08-16 22:47 ` Linus Torvalds
2009-08-17 1:53 ` Pádraig Brady
2009-08-17 10:51 ` Giuseppe Scrivano
2009-08-17 15:44 ` Steven Noonan
2009-08-17 16:22 ` Linus Torvalds
2009-08-17 21:43 ` Steven Noonan
2009-08-17 17:32 ` Giuseppe Scrivano
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