Re: Another problem with stream reading.

["Randy Brukardt" <randy@rrsoftware.com>]

David Bolen wrote in message ...
>"Randy Brukardt" <randy@rrsoftware.com> writes:
>
>> Janus/Ada, at least, will generate code for your type byte as if it
is
>> unsigned (that has necessary for Ada 83, which had no unsigned types
at
>> all), with all of the checking. But where the language requires the
base
>> type (such as in streams), we have to use signed 16-bits.
>>
>> The place this matters, of course, is for the largest unsigned type.
If
>> you declare
>>             type Unsigned is range 0 .. (2**32)-1;
>> in Janus/Ada for Windows, you'll get an error, because there is no
>> signed base type large enough to fit it.
>
>How would you typically work around this, if you really wanted to be
>working with 32-bit unsigned quantities in your code?  If there's no
>signed base type large enough (sans 64-bit support presumably) would
>you have to implement your own set of operations on, say, a data type
>made out of two 16-bit values?


Portably, I think you'd have to do something like that.

Another option would be to use a 32-bit modular type, and do overflow
checking explicitly. For instance, for "+", if the result is smaller
than either of the operands, you've overflowed. Doing that for "*" is
unpleasant (you pretty much have to emulate the multiply), but its easy
for all of the other operations. It would be easy to define a package
like that (that is essentially how the Janus/Ada compiler handles value
for code generation purposes).

A pragma or something to get to the code generator's DW type would
probably be the best solution for Janus/Ada, since that would use the
processor's carry flag to do the overflow check. But of course that
wouldn't be portable.

                Randy.