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RE: crc32() optimization



> 
> On Mon, 2002-11-11 at 13:18, Joakim Tjernlund wrote:
> > Yes CRC is a pig, this is why I am trying to do something about it.
> > I think there is more to gain if you look at Algorithm 4 at  
> > http://www.cl.cam.ac.uk/Research/SRG/bluebook/21/crc/node6.html#SECTION00060000000000000000
> > since the current algorithm basically is Algorithm 3 in above link.
> 
> gcc knows about loop unrolling. On x86 your code appears to be slower
> since it uses more space and the compiler knows not to unroll it.

hmm, is unrolling arch specific? I hope not. Maybe it's my compiler, I am using 
2.95.3 from Monta Vista.

How much is the x86 code unrolled? I tried 16,8,6 and 4 as unroll steps and 6 was the
fastest for JFFS2(Note, I am no unroll expert, so therefore my questions may be a bit "strange").

Anyone else that has tried? Results?

   Jocke

 


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