>> Is there any guarantee that right-shift is signed when using gcc?
>
> I suppose so, I believe this is assumed to be that way in various other
> places.
> However, I'm not sure I have an idea where I could look up implementation
> defined behavior for gcc.
Looking into it a bit I think a compiler has to be consistent (i.e., it is
implementation *defined*) and gcc makes reasonable effort to do signed
shifts on architectures that have ISA support for it. I may add a boot-time
BUG_ON() just as a sanity check. :-)
> Sure, should work too, but would incur more overhead. I was actually trying
> to even avoid the two shifts, but I wasn't able to find something that would
> use just one *and* would be faster than the version I submitted.
I don't think it's possible. Two shifts and a compare is pretty tight.
 -- Keir
>
> Jan
>
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