Why are some casts from floating point to integral done differently

[Bane]

> The Digital Mars C compiler was started in 1982, and a lot of it still survives 
> in the code base (library & compiler).
> 
> The evolution of the human brain is not done by replacing structures with new 
> ones, but by putting new layers over the old ones and overriding them. Hence, we 
> all have a notochord, and a dinosaur brain, etc. You can see that in the back 
> end code; the original design and structure is intact, it's just been layered 
> over. Maybe some day I should dig up NWC 1.0 and post it!
> 
> The D front end, however, is radically different from the C front end.

If by some impossible way you could travel back in time to `82, could hardware support D if you would build it then?