On Mon, Dec 08, 2014 at 02:17:45PM +0000, Dave Gordon wrote:
> On 08/12/14 13:59, Damien Lespiau wrote:
> > On Mon, Dec 08, 2014 at 02:33:57PM +0200, Jani Nikula wrote:
> >>> #define _MASKED_BIT_ENABLE(a) (((a) << 16) | (a))
> >>> #define _MASKED_BIT_DISABLE(a) ((a) << 16)
> >>> +#define _MASKED_FIELD(value, mask) (((mask) << 16) | (value))
> >>
> >> Obligatory bikeshed, wouldn't you say _MASKED_BIT_{ENABLE,DISABLE} are
> >> special cases of _MASKED_FIELD...? ;)
> >
> > That's because we're not just enabling or disabling bits here but
> > setting a multi-bits value.
> >
> > _MASKED_FIELD(2 << 4, 0x3 << 4);
> >
>
> So you could
>
> #define __MASKED_BIT_DISABLE(a) (__MASKED_FIELD(0, (a)))
> #define __MASKED_BIT_ENABLE(a) (__MASKED_FIELD((a), (a)))
>
> which I think is what Jani was referring to ...
>
> Bikeshed++: do we care about the double evaluation of (a) in these macros?
Oh of course, misread that. We could also avoid the double evaluation
indeed and chris suggests (on IRC) BUILD_BUG_ON(bit & ~mask); (super
good!)
--
Damien
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