Re: [PATCH] Teach git-apply about '-R'

From: Linus Torvalds <torvalds@osdl.org>
Date: Jul 28, 2006, 15:14 UTC
Message-ID: <Pine.LNX.4.64.0607280809550.4168@g5.osdl.org>
In-Reply-To: <Pine.LNX.4.63.0607281213250.29667@wbgn013.biozentrum.uni-wuerzburg.de>

On Fri, 28 Jul 2006, Johannes Schindelin wrote:

>
> +/* a and b may not overlap! */
> +static void memswap(void *a, void *b, unsigned int len)

This is disgusting.

Especially since it's also slow as hell.

Show 9 quoted lines

> +		memswap(p->new_name, p->old_name, sizeof(char *));
> +		memswap(&p->new_mode, &p->old_mode, sizeof(unsigned int));
> +		memswap(&p->is_new, &p->is_delete, sizeof(int));
> +		memswap(&p->lines_added, &p->lines_deleted, sizeof(int));
> +		memswap(p->old_sha1_prefix, p->new_sha1_prefix, 41);
> +
> +		for (; frag; frag = frag->next) {
> +			memswap(&frag->newpos, &frag->oldpos, sizeof(int));
> +			memswap(&frag->newlines, &frag->oldlines, sizeof(int));

All but one of those are register sizes, so doing a horribly ugly "memswap()"to do them is truly nasty, when you could have done

	#define swap(a,b) myswap((a),(b),sizeof(a))

	#define myswap(a,b,size) do {		\
		unsigned char mytmp[size];	\
		memcpy(tmp, &a, size);		\
		memcpy(&a, &b, size);		\
		memcpy(&b, mytmp, size);	\
	} while (0)

and it would have worked MUCH more efficiently, since any sane compiler would immediately have noticed that you're doing word-sized copies, and optimized the hell out of it.

(Untested, of course).

		Linus