Re: cvs commit: src/sys/i386/include endian.h

From: Peter Wemm <peter_at_wemm.org>
Date: Tue, 23 Sep 2003 09:45:31 -0700
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_at_wemm.org; peter_at_FreeBSD.org; peter_at_yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
Received on Tue Sep 23 2003 - 09:45:32 UTC