[RC5] keyrate stabilizing?

Bruce Wilson bwilson at distributed.net
Mon Oct 22 07:47:11 EDT 2001


A shift is useful for multiplying and dividing by powers of two, a
rotate is not.

8-bit examples:

10010111	Sample
00101110	left shift (carry would be set)
00101111	left rotate (carry unaffected)
01001011	right shift
11001011	right rotate

__
Bruce Wilson <bwilson at distributed.net>
PGP KeyID: 5430B995, http://www.toomuchblue.com/ 

"Quidquid latine dictum sit, altum viditur."
(Whatever is said in Latin sounds profound.) 



| -----Original Message-----
| From: owner-rc5 at lists.distributed.net 
| [mailto:owner-rc5 at lists.distributed.net] On Behalf Of Test Man
| Sent: Monday, October 22, 2001 01:34
| To: rc5 at lists.distributed.net
| Subject: Re: [RC5] keyrate stabilizing?
| 
| 
| Is it really true that some CPUs do not have rotate
| instructions? I mean, a rotate is effectively a shift
| register - which is one of the fundamental blocks of
| digital electronics. Even the Sinclair ZX80 had one!
| And rotate/shift instructions are a very quick way of
| multiplying or dividing by powers of 2.
| 
| Sorry if I'm out of place on this one or if it has
| already been covered, but I've just joined the list.
| 
| --- Zorba the Hutt <zorbathut at uswest.net> wrote:
| > 
| > Yeah, but how much CPU does SSL/SSH really take up?
| > I used SSH a little on
| > my P166, and I didn't exactly have to shut down all
| > my programs. Not only
| > that, but with the ever-tightening encryption laws,
| > perhaps focusing on
| > making the (already-fast) encryption even *faster*
| > isn't a good use of their
| > time.
| > 
| > The people who use CPU power are, for the vast
| > majority, gamers,
| > programmers, artists, and people who need lots of
| > servers. The only one of
| > those who cares about rotating bits is the last, and
| > only if they're doing
| > encryption.
| > 
| > It just plain isn't worth it.
| > 
| > -Zorba
| > 
| > ----- Original Message -----
| > From: "Christopher Hicks" <chicks at chicks.net>
| > To: <rc5 at lists.distributed.net>
| > Sent: Saturday, October 20, 2001 10:40 AM
| > Subject: Re: [RC5] keyrate stabilizing?
| > 
| > 
| > > On Fri, 19 Oct 2001, Dan Sugalski wrote:
| > >
| > > > While rotates are useful in this case, and a few
| > other isolated
| > > > places, this is such an edge case that it's just
| > not worth the silicon
| > > > that it'd take to implement a rotate
| > instruction. Not having one
| > > > simplifies the ALU a bunch, and that speeds up
| > the core and leaves
| > > > more room for other things.  Even if a CPU fakes
| > it, like the newest
| > > > intel and AMD chips likely do, you still get a
| > win. (Heck, if all
| > > > tossing rotate out got you was another line in
| > your L1 cache it'd be
| > > > worth it...)
| > >
| > > In this day and age I would think that working
| > well on encryption would be
| > > more of a priority for CPU designers.  It hardly
| > seems like an edge
| > > application to someone that uses ssl and ssh on a
| > daily basis.
| > >
| > > --
| > > </chris>
| > >
| > > Neither sweat, nor blood, nor frustration, or
| > lousy manuals
| > > nor missing parts, or wrong parts shall keep me
| > from my task.
| > >
| > > --
| > > To unsubscribe, send 'unsubscribe rc5' to
| > majordomo at lists.distributed.net
| > > rc5-digest subscribers replace rc5 with rc5-digest
| > >
| > >
| > 
| > --
| > To unsubscribe, send 'unsubscribe rc5' to
| > majordomo at lists.distributed.net
| > rc5-digest subscribers replace rc5 with rc5-digest
| > 
| 
| 
| __________________________________________________
| Do You Yahoo!?
| Make a great connection at Yahoo! Personals.
| http://personals.yahoo.com
| --
| To unsubscribe, send 'unsubscribe rc5' to 
| majordomo at lists.distributed.net
| rc5-digest subscribers replace rc5 with rc5-digest
| 
| 

--
To unsubscribe, send 'unsubscribe rc5' to majordomo at lists.distributed.net
rc5-digest subscribers replace rc5 with rc5-digest



More information about the rc5 mailing list