[RC5] [ANNOUNCE] Notes about improved MMX DES cores

Jeff Lawson bovine at distributed.net
Sun Jul 12 07:10:34 EDT 1998


As there seems to be a fair amount of discussion regarding the new speed
improvements in the Intel x86 clients (build 415+), I'd just like to
clarify.  Yes in fact MMX instructions are able to be used to gain the
rather dramatic speed increases (that have been posted by others already on
the list).  The new MMX core was produced by Remi Guyomarch and Bruce Ford
using a bitslicing technique based off of the Kwan s-boxes, which are used
as the basis for our DES cores on most of the other non-x86 clients.  If the
client detects that your processor is MMX capable, the MMX core will be used
instead of the traditional BrydDES core.  Note that BrydDES does not use a
bitslicing technique at all, but instead uses a heavily optimized checking
method that incorporates a number of specialized techniques for gaining its
speed.  The effect of the MMX-optimizations are visible most significantly
on Pentium-II machines.  Currently the MMX optimizations only apply to the
DES core.  No way to utilize MMX instructions to aid RC5-64 has yet been
developed.

New MMX-optimized clients have been produced for only a few x86 platforms so
far.  Due to the significant speed gains in DES, all participants are
encouraged to keep an eye out for the release of a MMX-optimized client for
their operating system if any of their machines are MMX-capable.

As a reminder, only builds 415 and above have the MMX optimizations
implemented.


Jeff

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