Re: RFC: 40 bit integer support

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Fri, 1 Jul 2011, Bernd Schmidt wrote:

>  * Should we add an __int40_t keyword, or just do a pushdecl for it?
>    The patch currently does the latter to match __int128_t, but
>    decimal float and fixed-point support uses keywords. This may make
>    a difference for (existing) code using "unsigned __int40_t".

My advice is neither, initially; leave it to the user to define typedefs 
using the mode (possibly providing a header that the user can include with 
-include).  __int128_t is legacy and undocumented, with the __int128 
keyword (from the x86_64 ABI) being preferred.  I also don't recommend 
adding any types to stdint.h (so eliminating a lot more of the 
complexity); there is no requirement to have those types there, and in 
any case libc's stdint.h is used in most cases instead of GCC's.

>  * The __INT40_C macros use a cast, since using a new suffix is likely
>    to conflict with something defined by a future standard. This means
>    they are not usable in CPP tests. The TI compiler defines them in
>    the same way, however, and mentions DR209.  The link they give is
>    defunct:
>      http://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/dr_209.htm

Don't try to understand anything about stdint.h with reference to C99 
versions before TC3; there were several defects fixed in the TCs.  DR#209 
was fixed by correcting the definitions of the types produced from certain 
macros.

Yes, you need a way of producing something usable in #if to define such a 
macro.  This is evidence that the type does not belong in stdint.h....

-- 
Joseph S. Myers
joseph@codesourcery.com