From: tlaronde@polynum.com
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] Integer arithmetic: some lessons
Date: Wed, 21 Apr 2010 22:19:46 +0200 [thread overview]
Message-ID: <20100421201946.GA424@polynum.com> (raw)
In-Reply-To: <dc0579fcc1179638e3a224ecc4c094a5@plan9.bell-labs.com>
On Wed, Apr 21, 2010 at 11:03:06AM -0400, geoff@plan9.bell-labs.com wrote:
> If you think that shift operators aren't being translated
> to shift instructions, you can examine the output of 8c -S.
>
> x/2 is equal to x>>1 for non-negative integer x; for negative x,
> the two expressions may yield different values, even if
> x is a signed integer. The book Hacker's Delight, among others,
> explores these sorts of optimisations.
Thanks for the reference. Having spent 3 days trying to understand
"generally" what was going on, I will now isolate one drawing that leads
to problem and add trace for gcc and for ken-cc to see where they do not
compute the same values. This will narrow the things and assembly, on
this, will give clues.
--
Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
http://www.kergis.com/
Key fingerprint = 0FF7 E906 FBAF FE95 FD89 250D 52B1 AE95 6006 F40C
next prev parent reply other threads:[~2010-04-21 20:19 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-21 13:40 tlaronde
2010-04-21 15:03 ` geoff
2010-04-21 20:19 ` tlaronde [this message]
2010-04-21 23:28 ` Bakul Shah
2010-04-22 5:51 ` tlaronde
2010-04-22 9:42 ` Steve Simon
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