The future of Int128 support in D language

[Iain Buclaw]

On Sunday, 8 January 2023 at 17:36:07 UTC, Johan wrote:
>
> I like that you splitted the implementation into a separate 
> file, that's a good idea.
>
> GDC also can benefit of a specialized implementation. Probably 
> good to ask Iain of how best to approach these specializations 
> (i.e. what files, how to forward to the specialized 
> implementation from the upstream druntime file, ...)
>
> -Johan

Actually, I had implemented core.int128 as compiler-recognized 
intrinsics that do the necessary conversion to/from native on the 
fly.

I ran into some problems when testing this on SPARC though (to 
name one non-x86 target that I use for sanity checking new 
code-gen features).  Never found the time to get to the bottom of 
what was causing it to crash, so left it as a TBD patch set.

I suspect I am going wrong somewhere with all the concatenated 
`*cast(cent*)&c` and `*cast(core.int128.Cent*)&c` going on all 
around the place when you chain these functions together with 
UFCS.  Maybe should investigate using a `union` instead, but not 
enough bandwidth to do that at the moment.