Word types..._(re)

Fri, 20 Jun 1997 15:38:03 +0200

Peter Gerwinski wrote:

> Where do such data types matter?  Everywhere where we must set up a record
> type of well-known size and structure, for example when reading a binary
> file created by some other program,

(* Not necessarily by another program. If the file can get big, I'd want to
   choose the smallest possible types, anyway. *)

> or when communicating with the operating
> system.
>
> For this reason, the syntax must be compact, and somehow closer to the bare
> metal (assembler) than to the clouds (Modula).  That's why I prefer `Word'
> here with respect to `Cardinal'.  (* Another reason is that when I read
> `Card', I think of games, not of cardinalship. ;*)

(* And when I read "Word", I think of other things, too... *)

> (Due to the need for
> compactness, I think my "Integer ( 8 )" notation was not the best idea.  Or
> perhaps it was, and the programmer can define the below in his own Units?)
> So what about this?
>
>     Int8    Word8 = Byte
>     Int16   Word16
>     Int32   Word32
>     Int64   Word64

If everyone can define these types, we don't have to determine it here.
You can declare "Word" in your units, and I'll probably declare
"Card" or perhaps "Cardinal" in mine...

> Once more discussing subranges as an alternative:  "True Pascal" does not
> specify the storage size, but valid values for those.  So I am no more sure
> whether it is wise to guarantee that their size will always be the minimal
> one.  And anyway, they are no true replacement for built-in data types of
> well-defined size because no programmer will write `0..$FF' everytime he
> wants to express that something has 8 bits.  He will define his own type
> for this reason: "Type Byte = 0..$FF".  (Note that `Byte' is built-in in
> GPC!)  If we don't want terrible confusion among future GPC hackers, we
> should provide built-in types for such purposes.

But you can't predefine anything that might be needed by someone. Perhaps
someone needs a type with the range 0..1234 that occupies 2 bytes...

So I'd prefer to have a way to define it by oneself. To me, the "packed"
still seems the most logical thing to do: without "packed", the data are
optimized for speed, with "packed" for size. So it would "only" be
necessary to extend "packed" to any type (and I don't see any inherent
reason why it should apply only to records and arrays).
-- 
Frank Heckenbach, Erlangen, Germany
heckenb@mi.uni-erlangen.de
Turbo Pascal:   http://www.mi.uni-erlangen.de/~heckenb/programs.htm
Internet links: http://www.mi.uni-erlangen.de/~heckenb/links.htm

Frank Heckenbach (heckenb@mi.uni-erlangen.de)