Re: [9fans] integer width on AMD64

[Comeau At9Fans <comeauat9fans@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1925 bytes --]

On Sat, May 5, 2012 at 10:58 PM, Joel C. Salomon <joelcsalomon@gmail.com>wrote:

> On 05/05/2012 05:06 PM, Comeau At9Fans wrote:
> > On Sat, May 5, 2012 at 1:48 PM, Charles Forsyth wrote:
> >
> >     if it's performance you're worried about, for programs that don't
> >     care about width, i'd expect 32 bits at least
> >     to match performance with 64 bits (if there's a measurable
> >     difference). for one thing, cache lines will contain
> >     more values, and several will be fetched at once when cache lines
> >     are filled.
> >
> > And for programs that do care about this, C99 provides things such as
> > int_fast64_t (which IIRC 8c et al does not currently support).
>
> <stdint.h> is just a bunch of typedef's, some of which have been
> included, under different names (u{8,16,32,64}int), in <u.h>.  Wouldn't
> be hard to provide for APE if anyone wants it.


Yes, the u{...}int names are important.  Those "different names" are
normally for other (though obviously related) purposes (conceptually
int_exact_*), and the int_least_* and int_fast_* names, usually are built
from the exact ones.  BTW, more generally re the greater issue raised
earlier by an OP, if ones intent is X bits, then int is not expressing that
intent, and even if your assumption happens to be correct, it might also
create a portability faux pas if that is a concern.  Also, if int was X
bits underneath, then arrays of int, now in the case of X == 64 effectively
become arrays of long stuff since not only is there now maybe wasted
memory, but cache management and such can be a concern.  This all has
architecture dependencies though.

--
Greg Comeau / 4.3.10.1 with C++0xisms now in beta!
Comeau C/C++ ONLINE ==>     http://www.comeaucomputing.com/tryitout
World Class Compilers:  Breathtaking C++, Amazing C99, Fabulous C90.
Comeau C/C++ with Dinkumware's Libraries... Have you tried it?

[-- Attachment #2: Type: text/html, Size: 2588 bytes --]