64 bit architectures and C/C++

[Clive Feather]

In article <1991May6.232116.11401 at sq.sq.com> msb at sq.sq.com (Mark Brader) writes:
> I disagree.  I think "long long" is a preferable approach.
[...]
> A programmer wishing
> to do arithmetic on integer values exceeding what can be stored in
> 32 bits has three options:
[...]
>   (c) use an integral type known to provide the required number of bits,
>       and never port the program to machines where no such type exists.
[...]
> Now, what would we like to happen if a program that assumed 64-bit
> integers existed was ported to a machine where they didn't?  We would
> like the compilation to fail, that's what!  Suppose that the implementation
> defines long to be 64 bits; then, to force such a failure, the programmer
> would have to take some explicit action, like
>
>	assert (LONG_MAX >= 0777777777777777777777);
>
> On the other hand, suppose that the implementation defines a separate
> "long long" type for 64-bit integers.  Then when the user compiles the
> program on the 64-bit machine, they get:
>
>	cc: warning: "long long" is an extension and not portable
>
> and, assuming a reasonable quality of implementation, they can eliminate
> this message with a cc option if desired.  And if they do try to port,
> they get a fatal error in compilation.
>
> This behavior seems exactly right to me.

If you want the compilation to fail, then what's wrong with the
following ?

    #if LONG_MAX < 0xFFFFffffFFFFffff
    ??=error Long type not big enough for use.
    #endif

This causes the compilation to fail only when long is not big enough,
does not require any new types in the implementation, and generates *no*
messages on an 64-bit-long system. 

Notes: the use of a hex, rather than octal, constant awith mixed case
makes it easier to count the number of digits, and the explicit trigraph
is used to choke (non-ANSI) implementations which don't have #error, and
which might object to it even when the condition of the #if is false.
-- 
Clive D.W. Feather     | IXI Limited         | If you lie to the compiler,
clive at x.co.uk          | 62-74 Burleigh St.  | it will get its revenge.
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