Re: [patch 1/13] Qsort

[Felipe Alfaro Solana]

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?

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/