Constant byteorder macros.

[H. Peter Anvin]

Oliver Xymoron wrote:
> 
> On Thu, 20 Jan 2000, H. Peter Anvin wrote:
> 
> > >  switch (status) {
> > >     case cpu_to_le16(CONSTANT_XYZ):
> > >
> > > ... I need to define new macros __constant_cpu_to_le16(), etc.
> >
> > Given that gcc has a __builtin_constant_p(x), you ought to be able to
> > do:
> >
> > #define cpu_to_le16(x) ( __builtin_constant_p(x) ? __constant_cpu_to_le16(x) : __cpu_to_le16(x) )
> 
> This is ugly and potentially means changing tons of macros. Couldn't you
> just do the appropriate byteswap on the switch variable instead? There
> aren't many (any?) other places in C aside from the preprocessor and array
> sizing that insist on constant expressions.
> 

So you'd rather waste optimization?

The definition may be ugly, but it works just fine.

	-hpa

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