Jesse Pollard <pollard@tomcat.admin.navo.hpc.mil> writes:
> >Jesse Pollard <pollard@tomcat.admin.navo.hpc.mil> writes:
> >> And even then it is limited to 64 bits on a 64 bit system (unless the
> >> compiler is non-standard - ie "long long" type of thing).
> >
> >long long is in ISO/ANSI C99.
>
> yes it is. but the number of bits is not. On a 32 bit system "long long" is
> 64 bits. On a 64bit system it is 128. And if you need more bits that
> that you are out of luck. "long long" is imprecise, I'd prefer a construct
> like "int var: 64". This way I know exactly how many bits are available.
> If I need 128 bits for something (or even 4096) then I can define them. Or
> is there going to be a "long long long long" for 128 bits, and "long long
> long long long long .... long" to reach 4096?
Indeed. I don't expect to ever find much use for long long, because
C99 also comes with <inttypes.h>. Granted, it's not quite as general
as the scheme you propose, but it looks like it will do.
(<inttypes.h> is in some ways more general than your scheme. If I say
"int var : 64", does that mean the smallest signed integer type
holding 64-bits, or the fastest one (e.g. one that can be held in a
register), or what? <inttypes.h> deals with this. Of course, your
scheme could easily be extended, but it shows that once you start to
add facilities for declaring variables based on type properties, there
are a lot more properties to consider than just bit-width. If you want
PL/I, you know where to find it ;-))
The main point of long long is that it guarantees that there will be a
64-bit type, and so <inttypes.h> has definitions for int64_t
etc. Since C99 does not require a 128-bit extended integer type,
<inttypes.h> does not have to define int128_t etc. But it does reserve
the namespace, and it would take a very brain-dead vendor to have such
a type but omit the corresponding definitions from <inttypes.h>.
The other advantage of <inttypes.h> is that, even for platforms
without long long, it is very easy to write your own version of that
file and use it in your own projects on non-C99 platforms. Similar
techniques are already widely used, of course; all C99 does is fix the
names.
David Wragg
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