speed of an AMD K6-2 350 was: ([RC5] Do we check for the Pentium bug?)

Greg Wooledge wooledge at kellnet.com
Wed Jun 9 19:47:00 EDT 1999

Alexander Bihlmaier (Thalunil at gmx.net) wrote:

> the AMD K6-2 with 350 Mhz produces only 550 KiloKeys / s. You say, that
> all the code of the d.net client is integer code. I thought AMD is in
> Integer code as fast or faster than Intel.
> Or it is just normal, when his AMD is so slow?

A better question is, why are Intel chips so fast at RC5?

The Intel chips have hard-coded variable bitwise rotate instructions.
The K5 does, too... but the K6 and K6-2 do not.  The K6's emulate the
x86 rotate instuctions in microcode, which makes the instruction take
longer than it does on an Intel chip (but less time than it would to
shift and mask the bits manually, as is necessary on many other chips).

RC5 uses the rotate instructions quite heavily -- so the Intel chips do
much better at RC5 than the newer AMD chips.

Try comparing the DES cracking rates, though, and you'll see that the
AMD and Intel chips are much closer.

Greg Wooledge                    | Distributed.NET http://www.distributed.net/
wooledge at kellnet.com             | because a CPU is a terrible thing to waste.
http://www.kellnet.com/wooledge/ |

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