[RC5] ia64 core?

Rolf Stals r.stals at oke.nl
Fri Mar 30 21:02:17 EST 2001


> IA64 can do IA32 in hardware.  The Itanium implementation of this
>architecture doesn't waste many transistors on this ridiculous job.  (I say
>ridiculous because if they were aiming to run IA32 code fast, they would
>have just made another IA32 CPU.  The point of IA64 is to say "screw all
>that backward compatibility, let's see what we can do without that
>boat anchor around our necks.")
>
> tweakers.net must have been running the stock IA32 core on the machine,
>which obviously is going to suck, and is totally meaningless.  There's no
>way to infer the performance of an IA64 binary from IA32 performance.

There are indeed not much testing programs for an IA-64 processors simply
because the fact no one has had the chanche to write because intel wouldnt
let them. What i can understand because their was a lot of research money
in this processor and they dont want other people to run of with their idea's

> You're saying that the lack of 64bit registers makes it hard to deal with
>an algorithm that uses 64bit keys.  (It wouldn't write to memory, and esp.
>not disk, just have to do more work shuffling register.)  However, rc5 never
>requires manipulating 64bit integers directly.  Everything is done by
>splitting the key in half, and doing stuff to each half, and XORing the
>halves, and stuff like that.  (The important point is that you don't need to
>do 64bit rotates, adds, or multiplies for rc5.  It was designed when common
>computers were 32bit, so it uses 32bit operations.  The rest of my
>description of how it works it totally bogus, since I don't have time to
>look up the RFC.)
>
> This being the case, you won't see a big speedup just from having a 64bit
>CPU.  If it's possible to have a 32bit quantity in the high half, and
>another in the low half, of the same register, and do stuff with them, then
>RC5 could go faster than it would on a similar CPU that had only 32bit
>registers.  Otherwise, the 64bit aspect isn't going to help much.  (it helps
>some, since you can move more bits at the same time, and you do sometimes
>have to copy around 64bit quantities.)

I couldnt have said it better myself :)
But like i said before, my english s*cks, but if you can understand dutch i
could explain all this perfactly.


>-- 
>#define X(x,y) x##y
>Peter Cordes ;  e-mail: X(peter at llama.nslug. , ns.ca)



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