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Re: [Xen-devel] code question?


On 11 Aug 2005, at 18:03, M.A. Williamson wrote:

I think that:
!!a & !b === (a != 0 ) && ( b == 0 )

It's just more efficient to do it directly using bitwise ops than to use the full logical operators (can gcc really not optimise this sort of thing???).

It can't optimise out short-circuit semantics. Without predicates on instructions (like e.g. ARM has) it has to emit conditional branches.

 -- Keir


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