Re: [Tinycc-devel] casting bug?

[Felix Nawothnig]

Alexander Strasser wrote:
> > Then we have "int" which is at least 16bit wide and should be the native 
> > register size (I dunno if the standard specifically says this but that's 
> > the way it was before the (x86) empire), so should be the "fastest" type 
> > (unless we talk about 8-bit CPUs for which ANSI C isn't really suited 
> > anyway :)
> Ah back on topic, int isn't native register size on x86_64 anymore.

That depends on the compiler and not on the architecture ofcourse. Also 
some compilers allow you to choose between LP64 / LLP64.

> And this breaks the assumption (which is afaik not really guaranteed
> by the standard) I and many others (including you) made.

Not for x86_64 as 32bit operations are just as fast as 64bit ones (in 
theory - gcc didn't properly optimize them but I think that was fixed 
recently (?)).

> > You can't have both a guaranteed size and guaranteed performance (while 
> > being portable), so what would your proposed "int_fast32_t" be then?
> It's not my proposed type, this exists already I don't know if it is
> covered by C99 or not. But the trick would be let's say on a 64bit arch
> and a compiler using LP64 model (int is normally 32bit in this case) you
> would still get a 64bit integer. It is not about having fixed 32 bits
> it is more about having a at least 32bit wide type.

I see, you mean what_int_ought_to_be_t and what_long_ought_to_be_t :-)

> Well, of course it is not optimal if you target 16bit architectures in
> that case you would have to use int_fast16_t.

Well, you rarely really need "at least 32bit" anyway (which is why it's 
called long) and most likely not in performance critical code...

> It's probably never really optimal, but it would be possible to use
> practically at least. Best would be if the modern 64bit systems would
> support for example the ILP64 model, and thus the good old int assumption
> would still hold. But i think that train has already left and is far away...

I don't think so. Most new (UNIX) code is written with portability in 
mind (often using the autotools), C99 usage (stdint) is widespread.

Most stuff would probably run with ILP64 - and for the stuff that 
doesn't a #pragma and/or a commandline switch could be introduced...

Or maybe I'm just a bit naive...

Felix