[RC5] AMD 3DNow enhancement?

Eric Gindrup gindrup at okway.okstate.edu
Thu Sep 10 22:49:37 EDT 1998


     The use of FPU code to crack RC5 has been suggested a couple of 
     times on this list.  I only know of one attempt, by Bruce Ford to 
     implement a core using this hardware.  I criticized it for using 
     non-pairable FPU instructions (i.e., the normal integer core 
     couldn't pair instructions with a low-throughput FPU extension).
     
     Some relevant dates and subject lines are:
     1997:
        late October     Why are Alpha's so much slower then wintel [...]
        mid November     A whole bunch of things
        early December   Ideas
                          [including a quote from the old FAQ which said 
                           that MMX was pointless as well.  Heh.]
        mid December     New Chips...
     1998:
        early January    Use of FPU on Intel 486 and P5 processors
     
     I'd suggest looking through the archives at 
     http://lists.distributed.net/ to find out what's been said about 
     this before.
     
     The original FPU idea was to write an FPU-exclusive core and compare 
     it to the integer core.  This wasn't really workable.
     
     The final idea for FPU-extended cores was to have the normal integer 
     core plodding away and then, in the "spaces" created by pipeline 
     stalls, insert FPU code that cracked keys very slowly.  This 
     wouldn't change the keyrate of the integer-based code at all.  
     However, it would allow a couple of percent of keyrate improvement 
     by implementing more parallel execution units.
     
     
     It is unfortunate that the FAQ at
     http://www.distributed.net/FAQ/rc5faq.html#TD00B0
     indicates that MMX can't be used to improve keyrate.  Similarly at
     http://www.distributed.net/FAQ/rc5faq.html#TD00A0
     the same sort of statement is made about the FPU.
     This is somewhat humorous given the recent release of the 
     MMX-enhanced cores...
            -- Eric Gindrup ! gindrup at okway.okstate.edu


______________________________ Reply Separator _________________________________
Subject: Re: [RC5] AMD 3DNow enhancement? 
Author:  <rc5 at lists.distributed.net> at SMTP
Date:    9/4/98 6:18 PM


On Fri, 04 Sep 1998, you wrote:
>I know that there're MMX enhancements for RC5/DES (and they've worked 
>well, AFAIK). However, are there any plans to add support for AMD's 3DNow 
>instruction set?
>	Obviously, these instructions are optimized for 3D gaming, but I would 
>think that there might still be a possibility due to their 
>heavy-floating-point nature.
     
Umm, well, if you've found a way to use floating point to help crack RC5, I'd 
be very interested to know about it... ;)
     
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