On Sat, 30 Mar 2013 18:01:32 +0800, RS said:
>
> Now I think this will spend more time than the kernel code when executed.
Have you actually examined the generated code on several popular
architectures to see what gcc actually does?
(hint - many things can constant-folded at compile time. So if
the 3 values are #defined to constants, the expression
(_IOC_NRSHIFT >> _IOC_NRBITS) - _IOC_NRSHIFT)
will generate no actual shift or subtract instructions, merely another
constant.
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