JFFS3 & performance

[Jörn Engel]

On Thu, 16 December 2004 20:58:55 +0100, Joakim Tjernlund wrote:
> > crc24:
> > real    0m0.969s
> > user    0m0.882s
> > sys     0m0.073s
> >
> >
> > Looks like those cold hard numbers beat the crap out of my previous
> > argument.  So unless someone can seriously optimize below functions,
> > just pick adler32.
> 
> A table driven crc24/crc16 is faster, I think.

Sure.  I'm just too lazy to create one.  (hint, hint)

> > uint32_t crc24(uint32_t crc, const void *_s, size_t len)
> > {
> > 	const char *s = _s;
> > 	uint32_t ret = crc;
> > 	strlen(s);
> 
> Why strlen()?

Leftover from my quick'n'dirty hacking.  Numbers without the strlen:
real    0m0.952s
user    0m0.878s
sys     0m0.068s

Not a big difference.

> 
> > 	for (; len; len--,s++) {
> > 		ret <<= 8;
> > 		ret += *s;
> > 		ret %= 0xfffffd;
> > 	}
> > 	return ret;
> > }
> 
> This is probably faster(on PPC).
> Depens on gcc version as well.
>
> uint32_t crc24(uint32_t crc, const void *_s, size_t len)
> {
> 	const char *s = _s-1;
> 	uint32_t ret = crc;
> 	if (len)
> 		do {
> 			ret <<= 8;
> 			ret += *++s;
> 			ret %= 0xfffffd;
> 		} while (--len);
> 	return ret;
> }

Not in i386, though.  So unless the tables really make a difference,
just don't bother.
real    0m0.954s
user    0m0.880s
sys     0m0.064s

Jörn

-- 
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