[rc5] Why are Alpha's so much slower then wintel boxe

Dan Sugalski sugalskd at osshe.edu
Fri Oct 31 16:50:02 EST 1997


At 06:25 PM 10/31/1997 -0600, Eric Gindrup wrote:
>
>     Oops.  Drop the last term from that long sum and add that the most 
>     significant byte is now useless.
>     
>     Also, I got a bit fuzzy about x.  It would have been better to say:
>     "Let abcdefgh be some 8-bit... and let x = [abcdefgh, 8-3-1]"  I was 
>     thinking I had said this in the rest of the message.  (*sigh*)

Your solution's slower than what we've got now, unfortunately. (Plus, since
we're rotating larger numbers (32 or 64 bits, IIRC) you may still run into
FP truncation/rounding issues) Faking a left rotate takes an AND, an OR, a
left shift, and a right one. (Not necessarily in that order :) You can do
it with a right rotate, too, but I don't think there's one of those around
in the Alphas either.

					Dan

----------------------------------------"it's like this"-------------------
Dan Sugalski                            even samurai
sugalskd at osshe.edu                      have teddy bears
                                        and even the teddy bears
                                        get drunk
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