`Word' data type et al._(re)

Wed, 18 Jun 1997 20:13:16 +0200 (MET DST)

According to Frank Heckenbach:
>
> > Cardinal        0 .. 65535      Non sign=E9, 16 bits
> >
> > Cardinal        0 .. 2147483647 Non sign=E9, 32 bits
> 
> [...]
> 
> That's fine! If Delphi uses "Cardinal", gpc should use it too,
> of course.

It already does.  32 bits, unsigned.  As you can see above,
`Cardinal' is 31 bits, unsigned, in Delphiy.  Has anybody an
idea, why?

> > Generic Types

GPC's current setting - on *all* platforms - is the following:

    GNU Pascal             GNU C

    Byte                   unsigned char
    ByteInt                signed char
    ShortWord              unsigned short
    ShortInt               short
    Integer                int, long
    Word, Cardinal         unsigned, unsigned long
    LongInt, Comp          long long
    LongWord               unsigned long long

I see only one possible reason why we should change that:  It is
not absolutely sure that `int' will always remain the same as `long'
on GCC.

The sizes of these types are the same on all platforms I have seen
so far.  (8, 8, 16, 16, 32, 32, 64, 64.)  However I agree that it is
a good idea to provide types of known size.

> > Well defined types
> >
> > int8      card8   (=3Dbyte is the only case without doubt)
> > int16     card16
> > int32     card32
> >
> > [...]
> 
> Sounds good.

I agree, but maybe a different syntax would be preferable.  UCSD Pascal
has a "long Integer" type which is written as

    Type Int42 = Integer [ 42 ];

Where `42' is the number of decimal digits.  (In the long run, this should
be in GPC, too.)  What about defining

    Type Int16 = Integer ( 16 );
    Type Word16 = Word ( 64 );

for types with a specified number of *dual* digits, read: bits?

...

=== BUT ===

What are we talking about?

Pascal has subrange types.  Why not forget about all this and let the
user specify the types by himself?

   Type
     I16 = -$8000..$7FFF;
     W16 = 0..$FFFF;

   MyRecordToAccessSomeStrangeSystemData = record
     Descriptor: 0..$FFFFFFFF;
     ImportantData: -$80..$7F;
     FillSpace: array [ 0..42 ] of 0..$FF;
   end (* MyRecordToAccessSomeStrangeSystemData *);

Then, of course, GPC must not reserve more space than necessary for
them - which it does not do anyway since it has packed records.
(These topics are related, as you can well imagine.)

> > Compatibility types
> >
> > anything contained in bpcompat.pas delphi1compat.pas
> > delphi2compat.pas and everything you need,
> > better than compiler switches when possible to
> > avoid to garble the compiler by a lot of special
> > purpose oddities: the idea of C to keep a minimum
> > in the compiler and a maximum in libraries is
> > not so bad (when it is possible).
> 
> I agree! Except for "integer", all types can be redeclared in these
> units. (I think, "integer" could be redeclared, too, but AFAIR it's
> not a good idea to do so, is it?)

It's not a good idea for the same reason as it is not a good idea to
change the size of `Integer' by a compiler switch.

    Peter

 Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer
peter.gerwinski@uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201]
 maintainer GNU Pascal [970510] - http://home.pages.de/~gnu-pascal/ [970125]

Peter Gerwinski (peter@agnes.dida.physik.uni-essen.de)