Hi, On Tue, 15 Jan 2008, Joseph S. Myers wrote:
> On Mon, 14 Jan 2008, Richard Guenther wrote: > > > Can you clarify on the resulting promotions? As I remember the > > standard defines promotions based on the representable values, so > > long : 15 gets promoted to int, but long : 33 doesn't get promoted. > > In the C++ FE at least we promote to the _declared_ type, that is, > > to long in this case. (Which I find more natural, but may be not > > what the standard says). > > Types (including the bit-field width as part of the type) narrower than > int are promoted based on representable values (so to int). Types wider > than int are left unchanged by the promotions. Right. And IMHO that's a deficiency. From a language esthetics perspective also those larger bit-fields should be promoted, namely to the next larger integer type (which surely exists for compilers implementing bit-fields larger than int). Doing arithmetic on small bit-fields on the (larger) promoted type, but doing them on large bit-fields on the exact width creates an asymmetry. That asymmetry then reflects into the code generator as ugly special cases, and actually also in horrible intermediate code (like doing bit mask operations after all arithmetic). So, if there's opportunity to fix the C standard in the next round by including language for promotions wider than int, that would be IMO much better than introducing first-class bit-field types. It would also mirror current behaviour of many compilers. Ciao, Michael.
