Re: crc32() optimization

["Joakim Tjernlund" <Joakim.Tjernlund@lumentis.se>]

Cool! I will give it a try(tomorrow afternoon) and see what happens.

         Jocke
> > 
> > What's "Duff's Device"?
> 
> It's a tricky way to implement general loop unrolling directly in  C.
> Applied  to your problem, code that looks like this (instead of 8 any
> other loop count may be used, but  you  need  to  adjust  the  "case"
> statements then):
> 
> register int n = (len + (8-1)) / 8;
> 
> switch (len % 8) {
> case 0: do { val = crc32_table ... ;
> case 7: val = crc32_table ... ;
> case 6: val = crc32_table ... ;
> case 5: val = crc32_table ... ;
> case 4: val = crc32_table ... ;
> case 3: val = crc32_table ... ;
> case 2: val = crc32_table ... ;
> case 1: val = crc32_table ... ;
> } while (--n > 0);
> }
> 
> BTW: this is strictly legal ANSI C!
> 
> For an explanation see http://www.lysator.liu.se/c/duffs-device.html
> 
> Best regards,
> 
> Wolfgang Denk
> 
> -- 
> Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
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