On Thu, Mar 17, 2016 at 07:40:59AM +0100, Heiner Kallweit wrote:
> Am 16.03.2016 um 23:28 schrieb Sean Young:
> > On Wed, Mar 16, 2016 at 10:18:38PM +0100, Heiner Kallweit wrote:
> >> +  u8              pulse:1;
> >> +  u8              reset:1;
> >> +  u8              timeout:1;
> >> +  u8              carrier_report:1;
> > 
> > Why are you changing the type of the bitfields? 
> > 
> I did this to make sure that the compiler uses one byte for
> the bit field. When testing gcc also used just one byte when
> keeping the original "unsigned" type for the bit field members.
> Therefore it wouldn't be strictly neeeded.
> 
> But I'm not sure whether it's guaranteed that the compiler packs a
> bit field to the smallest possible data type and we can rely on it.
> AFAIK C99 is a little more specific about this implementation detail of
> bit fields but C89/C90 is used for kernel compilation.

It might be worth reading about structure packing rules rather than
guessing.


Sean
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