On Sun, Jan 23, 2005 at 03:03:32AM +0100, Felipe Alfaro Solana wrote:
> On 22 Jan 2005, at 22:00, vlobanov wrote:
>
> >Hi,
> >
> >I was just reading over the patch, and had a quick question/comment
> >upon
> >the SWAP macro defined below. I think it's possible to do a tiny bit
> >better (better, of course, being subjective), as follows:
> >
> >#define SWAP(a, b, size) \
> > do { \
> > register size_t __size = (size); \
> > register char * __a = (a), * __b = (b); \
> > do { \
> > *__a ^= *__b; \
> > *__b ^= *__a; \
> > *__a ^= *__b; \
> > __a++; \
> > __b++; \
> > } while ((--__size) > 0); \
> > } while (0)
> >
> >What do you think? :)
>
> AFAIK, XOR is quite expensive on IA32 when compared to simple MOV
> operatings. Also, since the original patch uses 3 MOVs to perform the
> swapping, and your version uses 3 XOR operations, I don't see any
> gains.
>
> Am I missing something?
No temporary variable needed in the xor version. mov and xor are
roughly the same speed, but xor modifies flags.
--
Mathematics is the supreme nostalgia of our time.
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