[alsa-devel] [RFC][PATCH] ELD routines and proc interface

[Wu Fengguang]

On Fri, Nov 14, 2008 at 08:43:59AM +0100, Takashi Iwai wrote:
> At Fri, 14 Nov 2008 15:38:56 +0800,
> Wu Fengguang wrote:
> > 
> > > > > > --- /dev/null
> > > > > > +++ sound-2.6/sound/pci/hda/hda_eld.c
> > > > > > +static inline unsigned char grab_bits(const unsigned char *buf,
> > > > > > +						int byte, int lowbit, int bits)
> > > > > > +{
> > > > > > +	BUG_ON(lowbit > 7);
> > > > > > +	BUG_ON(bits > 8);
> > > > > > +	BUG_ON(bits <= 0);
> > > > > 
> > > > > Can it be rather BUILD_BUG_ON(), BTW?
> > > > > Or, hmm, doesn't work if it's an inline function?
> > > > 
> > > > Yes, converted to BUILD_BUG_ON() and it compiles OK.
> > > 
> > > The question is whether this really triggers the build error
> > > properly.  Could you check it, simply by changing the caller of
> > > grab_bits() with some invalid values?  Then you should get a compile
> > > error.
> > 
> > BUILD_BUG_ON() won't emit errors! So use BUG_ON()?
> 
> Try to make grab_bits() a macro and check whether BUILD_BUG_ON()
> works.  I think it won't be too bad to use a macro for such a pretty
> simple case.  If the resultant code looks too ugly, we should switch
> back to BUG_ON().

OK, I'm fine with a macro.

> The difference is that BUILD_BUG_ON() would add no real code while
> BUG_ON() is a pure run-time check.

But the code should be optimize away by gcc when the constant
expression is false? 

Thanks,
Fengguang