On Tue, Sep 10, 2013 at 2:51 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 09/10/2013 02:43 PM, Linus Torvalds wrote:
>
> Actually, the right thing here really is "er" (which I think you meant,
> but just to make it clear.)
Yes, I was just answering the i-vs-e confusion.
> "e" doesn't work on versions of gcc older than the first x86-64 release,
> but we don't care about that anymore.
Indeed.
> A final good question is if we should encapsulate the add/inc and
> sub/dec into a single function; one could easily do somethin glike:
Yes. However, I would do that at a higher level than the one that
builds the actual functions.
That said, there's a few cases where you might want to specify
add-vs-sub explicitly, but they are rather odd, namely the fact that
"-128" fits in a byte, but "128" does not.
So it can be better to add 128 by doing a "subl $-128" than by doing
an "add $128".
But we probably don't have any situation where we care about that
special value of "128". I've seen the trick, though.
Linus
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