integers of 1, 2, 4 bytes

[hreba <hreba@terra.com.br>]

Hi,

I want to translate some of my Oberon programs to Ada.

So I need the Oberon types SHORTINT (1 byte), INTEGER (2 bytes) and 
LONGINT (4 bytes). A type BYTE (1 byte, values 0..255) would be useful 
too. In Oberon one uses CHAR for that.

The most obvious translation for INTEGER would be

   type INT is range -32768 .. 32767;

(all platforms I have been working on use the two's complement).

My Ada book says that range checks are applied to constrained subtypes 
(like that one) but not to unconstrained subtypes, but but overflow 
checks are applied nevertheless. So I came up with

   type Int16 is range -32768 .. 32767;
   for Int16'Size use 16;
   type INT is new Int16'Base;

as a more efficient definition.

Now it seems the range specification doesn't matter any more and that I 
could equally write

   type Int16 is range -1 .. 1;
   for Int16'Size use 16;
   type INT is new Int16'Base;

Would you really define a 16 bit integer type this way?

And how about non-negative types? Would the following have the values
0 .. 255?

   type Nat8 is range 0..1;
   for Nat8'Size use 8;
   type BYTE is new Nat8'Base;
-- 
Frank Hrebabetzky		+55 / 48 / 3235 1106
Florianopolis, Brazil