[HARDWARE] Re: PPC rotate w/ mask

Dan Oetting oetting at gldmutt.cr.usgs.gov
Mon Oct 4 12:49:59 EDT 1999


>Bernie,
>
>I was looking at the PPC instructions for programmable rotates.
>I think it has five operands.  One of the operands is a mask
>for conrolling which bits are rotated.  I am not sure what
>performance increase this would get you; I didn't have enough
>time to look at it more closely.
>
>Stoney
>
Since RC5 need all 32 bits the mask isn't used in the rotates. What helps
the most is having a 32 bit dynamic rotate, 32x32bit general purpose
registers, two integer operations per clock cycle and an inner loop in the
PPC RC5 core that takes advantage of it all.

--
Dan Oetting <dan_oetting at comug.com>

PowerPC 603/604/750 -- Still the fastest RC5 core on the net.
(...but not for long)


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