From: david.brown@hesbynett.no   
      
   On 01/12/2025 17:56, Keith Thompson wrote:   
   > David Brown  writes:   
   > [...]   
   >> (I am not entirely sure, but I think it is standards-conforming for an   
   >> implementation to haev BITINT_MAXWIDTH set to 64 and support all   
   >> _BitInts up size 64, and then also support _BitInts of multiples of 64   
   >> thereafter.  Use of _BitInt greater than BITINT_MAXWIDTH is UB in the   
   >> standard - so an implementation can choose to give that a defined   
   >> behaviour for specific sizes.)   
   > [...]   
   >   
   > No, _BitInt(N) where N > BITINT_MAXWIDTH is a constraint violation.   
   >   
   > N3220 6.7.3.1p2 ("Constraints") :   
   >   
   >      The parenthesized constant expression that follows the _BitInt   
   >      keyword shall be an integer constant expression N that specifies   
   >      the width (6.2.6.2) of the type. The value of N for unsigned   
   >      _BitInt shall be greater than or equal to 1. The value of N   
   >      for _BitInt shall be greater than or equal to 2.  The value of   
   >      N shall be less than or equal to the value of BITINT_MAXWIDTH   
   >      (see 5.2.5.3.2).   
   >   
   > As I mentioned before, there's a proposal for C2y to allow   
   > signed _BitInt(1).   
   >   
   > Of course an implementation could do what you suggest as an extension.   
   >   
      
   Yes, of course - violating a constraint is UB, but it also requires a   
   diagnostic.  So while an implementation could implement a limited   
   selection of _BitInt's larger than BITINT_MAXWIDTH, if it is to conform   
   to the C standards it would have to at least give a warning message when   
   you used these _BitInt's.  As an extension (perhaps enabled by a flag),   
   it could then suppress such diagnostics.   
      
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