[RC5] SGI weird performance

Joe Zbiciak j-zbiciak1 at ti.com
Fri Jun 5 02:26:58 EDT 1998


'Max' said previously:

| Why are the SGI so slow ?? Other applications on them are way much
|faster than Intel machines ...

Part of the reason is that the MIPS family of processors do not have a
rotate instruction, whereas the x86 and PPC families do.  (This is a
FAQ question.)

The RC5 algorithm relies on the following three operations for its
encryption steps, primarily:  Rotate Left,  2's Complement Add, and
Exclusive Or.  Since the MIPS processor does not have a hardware rotate
instruction, the rotate must be synthesized with a subtract, two shifts
and an add.  This slows the client down.  (The same is true for most of
the RISC platforms, actually.)

Still, the numbers sound a little low.  The Sparc 20's here at work get
better key rates.  Question for the d.net folks:  Are the MIPS clients
written in optimized assembly, or are they compiled from C code?

Regards,

--Joe


-- 
  +------- Joseph Zbiciak ------+
  |- - - j-zbiciak1 at ti.com - - -|  "The ability to quote is a serviceable
  | -Texas Instruments, Dallas- |   substitute for wit."
  |- - #include <disclaim.h> - -|                  -- W. Somerset Maugham
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