Date: Tue, 23 Sep 2003 09:45:31 -0700 From: Peter Wemm <peter@wemm.org> To: Robert Watson <rwatson@FreeBSD.org> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/i386/include endian.h Message-ID: <20030923164531.6AC882A8DA@canning.wemm.org> In-Reply-To: <Pine.NEB.3.96L.1030923103120.82831A-100000@fledge.watson.org>
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Robert Watson wrote:
>
> On Mon, 22 Sep 2003, Peter Wemm wrote:
>
> > Microoptimization to allow the compiler to evaluate ntohl() etc on
> > known constants at compile time rather than at run time. We have a numbe
r
> > of nasty hacks around the place to cache ntohl() of constants (eg: nfs).
> > This change allows the compiler to compile-time evaluate ntohl(1) as
> > 0x01000000 rather than having to emit assembler code to do it. This
> > has other smaller flow-on effects because the compiler can see that
> > ntohl(constant) itself has a constant value now and can propagate the
> > compile time evaluation.
>
> So should we now be doing a sweep through the tree to remove instances of
> this? I.e.:
>
> /*
> * To avoid byte-swapping the same value over and over again.
> */
> igmp_all_hosts_group = htonl(INADDR_ALLHOSTS_GROUP);
> igmp_all_rtrs_group = htonl(INADDR_ALLRTRS_GROUP);
>
> Etc?
It is probably premature to do that just yet (only 2 of 5 or so platforms
handled), but that was the kind of "optimization" that prompted this.
NFS is also riddled with this.
Cheers,
-Peter
--
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
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